Greater thermoregulatory strain in the morning than late afternoon during judo training in the heat of summer.

PURPOSE: The time-of-day variations in environmental heat stress have been known to affect thermoregulatory responses and the risk of exertional heat-related illness during outdoor exercise in the heat. However, such effect and risk are still needed to be examined during indoor sports/exercises. The current study investigated the diurnal relationships between thermoregulatory strain and environmental heat stress during regular judo training in a judo training facility without air conditioning on a clear day in the heat of summer.
METHODS: Eight male high school judokas completed two 2.5-h indoor judo training sessions. The sessions were commenced at 09:00 h (AM) and 16:00 h (PM) on separate days.
RESULTS: During the sessions, indoor and outdoor heat stress progressively increased in AM but decreased in PM, and indoor heat stress was less in AM than PM (mean ambient temperature: AM 32.7±0.4°C; PM 34.4±1.0°C, P<0.01). Mean skin temperature was higher in AM than PM (P<0.05), despite greater dry and evaporative heat losses in AM than PM (P<0.001). Infrared tympanic temperature, heart rate and thermal sensation demonstrated a trial by time interaction (P<0.001) with no differences at any time point between trials, showing relatively higher responses in these variables in PM compared to AM during the early stages of training and in AM compared to PM during the later stages of training. There were no differences between trials in body mass loss and rating of perceived exertion.
CONCLUSIONS: This study indicates a greater thermoregulatory strain in the morning from 09:00 h than the late afternoon from 16:00 h during 2.5-h regular judo training in no air conditioning facility on a clear day in the heat of summer. This observation is associated with a progressive increase in indoor and outdoor heat stress in the morning, despite a less indoor heat stress in the morning than the afternoon.

Introduction

A greater thermoregulatory strain (i.e. higher body temperature and heart rate [HR]) has been reported in the morning exercise session from 09:00 h than in the late afternoon exercise session from 16:00 h in high school athletes during 3-h moderate-intensity baseball training [1] and 2-h high-intensity football training [2] in the heat outdoors under a clear sky. Given that there were no time-of-day differences in ambient temperature (Ta) and wet-bulb globe temperature (WBGT) between the sessions, these observations occurred because of the differences in environmental heat stress during exercise which increased with rising solar radiation and elevation angle in the morning but decreased with falling solar radiation and elevation angle in the late afternoon [1, 2]. Otani and colleagues [1, 2] therefore concluded that 2–3 h moderate- to high-intensity exercise in the heat of summer under a clear sky may be at a relatively higher risk for developing exertional heat-related illness in the morning from 09:00 h than in the late afternoon from 16:00 h. Those conclusions indicate that the diurnal variations in environmental heat stress affect thermoregulatory responses and the risk of exertional heat-related illness during outdoor exercise in a hot environment. However, such effect and risk are still needed to be examined during indoor sports/exercises.

Judo is a popular combat sport in junior high school and high school athletics in Japan. Judo has been reported to have one of highest numbers of exertional heat-related illness among school organized sports activities in Japan [3]. This is possibly due to a luck of air conditioning in the most judo facilities owing to its high running costs. Hence, majority of judo training sessions during the summer are performed under severe heat stress conditions, including high Ta and relative humidity (RH). This means that an increase in outdoor heat stress raises indoor heat stress in a judo facility in the heat of summer. Sport-specific characteristics of judo may also be responsible for increasing the risk of heat-related illnesses, since judo has high-density efforts and is a high-intensity sport [4] that requires a high-level of strength and endurance performance [5]. Moreover, there are seven weight divisions in judo and athletes are generally required to lose weight before competitions which may induce cumulative dehydration or hypohydration. Also, heavier weight class judokas have high body mass index which produces more metabolic heat and is less efficient in dissipating heat during exercise [6]. Both dehydration/hypohydration and high body mass index have been recognised as a thermoregulatory challenge and a higher risk for developing exertional heat-related illness during exercise in the heat [6]. To our knowledge, only one study has reported the impact of regular judo training on physiological responses in no air conditioning facility in the summer [7]. However, the study [7] was limited to the assessment of hydration status during 90 min regular judo training under a moderate heat stress (29.5°C Ta). Therefore, no study has investigated the effect of time-of-day changes in indoor and outdoor heat stresses on thermoregulatory responses during regular judo training in a facility without air conditioning in the heat of summer.

The aim of the current study was therefore to investigate the diurnal relationships between thermoregulatory responses and indoor and outdoor heat stresses during regular judo training in a judo training facility without air conditioning in the heat of summer. We hypothesised that thermoregulatory strain during the training would be greater in the morning than in the late afternoon due to a progressive increase in heat stress in both indoor and outdoor environments during the morning.

Methods

Participants

Participants were eight healthy, heat-acclimatized males who belonged to a high school judo team (mean±standard deviation [SD]; age 16.5±1.0 y, height 167±6 cm, body mass 66±11 kg, BMI 23±4 kg·m−2, years of training 6±2 y). All data collections were completed in August to ensure that participants were naturally acclimated to the heat. Their weight divisions were 2 extra lightweight, 1 half lightweight, 2 lightweight, 2 half middleweight and 1 middleweight. They trained ~5 days per week and performed a similar protocol of training in the current study more than 12 weeks. All participants and their parents received written information regarding the nature and purpose of this study prior to participation in the study. Following an opportunity to ask questions, a written statement of consent was signed by their parents. The protocol employed was approved by the local Ethics Advisory Committee of Himeji Dokkyo University (REF: 19–05) and was conducted in accordance with principles of the Declaration of Helsinki.

Experimental protocol

All participants completed two 2.5-h regular judo training sessions in a judo facility. A building was located approximately 15 m from the north side of the facility; however, there were no obstructions to shield the sun within a 50 m radius from the east, south and west sides of the judo facility. The judo facility was a one-story building with a floor space of 225 m2 (15 m × 15m). The judo facility had no air conditioning and there were windows on east and west sides of the wall, which were kept open during the sessions. The sessions were commenced at two different times-of-day: 09:00 h (AM) and 16:00 h (PM). The present study was conducted in early-August on a completely clear day, and PM trial was conducted first and AM trial was carried out two days later. A normal training session took place two days before the first trial (PM trial) but no exercise was permitted during the 24 h prior to the trials. Participants were dressed in the same judo uniform (jacket, pants, belt) in both trials. In the current study, participants wore a T-shirt under the judo uniform to protect surface skin temperature thermistor probes at the chest and upper arm during the sessions. This judo ensemble was 2.5±0.1 kg of total weight. There were no studies reporting the intrinsic clothing insulation (Rcl), the clothing area factor (fcl) and the evaporative resistance of clothing (Re,cl) of judo uniform. The present study therefore used the similar clothing to estimate Rcl, including 0.18 clo of short sleeve, sport shirt, 0.50 clo of double-breasted suit, jacket (denim), and 0.32 clo of straight, long, loose (denim) [8]. A clo is a unit of thermal insulation for clothing: one clo can be defined as the amount of insulation that allows the transfer of 1 W·m−2 with a temperature gradient of 0.155°C between two surfaces (0.18°C·m2·h·kcal−1). Total Rcl was calculated as 0.77 × the sum of these Rcl [8]. The fcl was calculated as (0.305 × total Rcl) + 1.0 [8]. As a result, total Rcl was 0.770 clo or 0.119 W·(m2·°C)−1 and fcl was 1.23. Since this total Rcl was similar to that of baseball uniform-temperate weather (0.762 clo) and football uniform-warm weather (0.795 clo) [9], the current study used Re,cl of these uniforms which were 0.022 W·(m2·kPa)−1.

Participants entered a laboratory which was close to the judo facility after a 2 h fast in each trial with the exception of plain water, which was allowed until 30 min before the start of the trials. Upon arrival, participants first emptied their bladder and thereafter nude body mass was measured to the nearest 10 g (AD6205B, A&D Co., Ltd., Tokyo, Japan). Surface skin temperature thermistor probes (ITP082-25, Nikkiso-Therm Co., Ltd., Musashino, Tokyo, Japan) were attached to four sites (chest, upper arm, thigh and calf) under the clothing without preventing range of motion. A weighted average of chest (0.3), upper arm (0.3), thigh (0.2) and calf (0.2) skin temperatures was used to calculate mean skin temperature (Tsk) [10]. Gastrointestinal thermometry has been shown to be a valuable device for core temperature (Tcore) assessment in the field and athletics settings [11]. However, the current study measured an infrared tympanic temperature (Tty) to estimate Tcore due to the restriction from pharmaceutical affairs law in Japan using gastrointestinal thermometry. Tty was measured using an infrared tympanic thermometer (GeniusTM 2, Covidien, Mansfield, MA, USA). In each measurement, two consecutive readings were obtained. All Tty measurements were taken by a single operator, using the recommended technique [12]. To avoid the increased effects of increasing Ta on Tty in the heat [13], the thermometer was stored inside a cooling box during the trial. The temperature inside this box was maintained by ice packs at about 25°C. Thermal sensation (TS) was measured using a 9-point scale [14]. All pre-exercise measurements were carried out in the laboratory in a temperate environment (25–27°C Ta) because prior heat stress exposure may increase thermoregulatory strain during subsequent exercise-heat stress in the morning than in the afternoon [15].

Participants then entered the judo facility and commenced a 2.5-h training session. Participants started the sessions in a dry judo uniform. Participants received airflow during the sessions which was directed from 3 corners to the centre of the facility by 3 industrial fans, using a 0.5 m blade diameter fan (SF-50FS-1VP, Suiden Co. Ltd., Sangocho, Osaka, Japan), to prevent high levels of hyperthermia during exercise in the heat [16]. Mean air velocity in the judo facility was about 2.5 km·h−1. Both training sessions were led by the same judo instructor to retain consistency between the two experiments. The content of training session in both trials was as follows: warm-up (20 min: running, dynamic-stretching and ukemi); newaza randori (25 min); rest (5 min); tachiwaza uchikomi (20 min); nagekomi (10 min); tachiwaza randori (40 min); waza practice (5 min); rest (5 min); strength training-own weight (15 min); and cool-down (5 min: static-stretching) (Fig 1). During the sessions, Tty and TS were assessed every 60 min and at the end of the training (Fig 1). To determine whole-body perception of effort, rating of perceived exertion (RPE) was assessed every 60 min and at the end of the training using the 6–20 RPE scale [17] (Fig 1). Skin temperatures (thermometer N543R, Nikkiso-Therm Co., Ltd., Musashino, Tokyo, Japan) and HR (HR monitor A370, Polar Electro, Kempele, Finland) were also recorded every 60 min and at the end of the training (Fig 1). Participants were free to ingest plain water maintained at about 30°C during the sessions. Following the sessions, participants returned to the laboratory, removed the probes and re-measured nude body mass to allow the estimation of total sweat loss.

Fig 1

Schematic representation of the experimental protocol.

Tty, infrared tympanic temperature; HR, heart rate; TS, thermal sensation; RPE, rating of perceived exertion.

Environmental measurements

Environmental conditions were measured at both inside and outside of the judo facility. Indoor environmental conditions were measured 1.5 m above the floor. Outdoor environmental conditions were measured 1.5 m above a dark asphalt pavement close to the judo facility. Ta, RH, black globe temperature (Tg), and WBGT were measured using a WBGT meter (WBGT-203A; Kyoto Electronics Industry Co., Ltd., Fukuchiyama, Kyoto, Japan) every 30 min. Air velocity was measured using an anemometer (AM-4214SD; Mother Tool Co., Ltd., Ueda, Nagano, Japan) facing the headwind every 30 min. Direct and diffuse solar radiation in the horizontal plane was recorded using a pyranometer (MS-01; Eko Instruments Co., Ltd., Tokyo, Japan) every 30 min, and solar radiation (global) was estimated by summing up the values.

Calculations

The equations of Tsk, mean radiant temperature (Tr), dry or sensible heat loss (DHL), evaporative heat loss (EHL), total heat loss (THL), absolute humidity, total sweat loss and age-predicted maximal HR (HRmax) are included in supporting information (S1 Data).

Statistical analyses

Data are presented as mean±SD. The significance level was set at P<0.05. The normality of the data and the homogeneity of variance between the trials were tested using Shapiro-Wilk’s test and Levene’s test, respectively. Non-parametric data (TS) were analysed using R (version 4.0.2). TS was analysed using a two-way (time-of-day [two levels, i.e., AM and PM] × time [four levels, i.e., 0, 60, 120 and 150 min]) repeated measures ANOVA with the R package nparLD (version 2.1) for the LD-F2 design. Pair-wise differences between trials were evaluated using the Tukey multiple comparison tests. In all other cases, statistical analyses of data were done in the IBM SPSS (version 21; IBM Corp., Armonk, N.Y., USA). Data collected once per trial were analysed using a one-way repeated measures ANOVA, and data collected over time were analysed using a two-way (time-of-day [two levels, i.e., AM and PM] × time [three or four levels, i.e., 0, 60, 120 and 150 min]) repeated measures ANOVA. Pair-wise differences between trials were evaluated using one-way ANOVAs with a Bonferroni adjustment applied for multiple comparisons. Environmental parameters were analysed using the independent (AM vs. PM) and dependent (indoor AM vs. outdoor AM; indoor PM vs. outdoor PM) samples t-test. Cohen’s d (d) was used as a measure of effect size for parametric paired samples; a d of 0.2 to <0.5 and ≥0.5 to <0.8 has been suggested to represent a small and medium treatment effect, respectively, while a d ≥0.8 represents a large treatment effect [18]. Spearman’s rank correlation coefficient (rs) was used to assess the relationship between the changes in Tty, Tsk and HR in each subject and the changes in Ta, WBGT, Tg, Tr, and solar radiation at 60, 120 and 150 min. A rs of <0.2 were considered a weak correlation, 0.21–0.4 were considered fair, 0.41–0.6 were regarded as moderate, 0.61–0.8 were deemed strong and 0.81–1.0 very strong [19].

Results

Pre-exercise body mass (P = 0.580), Tsk (P = 0.349) and HR (P = 0.247) were not different between trials, but pre-exercise Tty was higher on PM than AM trial (P<0.001; 1−β = 1.00; d = 1.51; Fig 2A).

Fig 2

Changes in infrared tympanic temperature (Tty; A), mean skin temperature (Tsk; B) and heart rate (HR; C) during exercise. *P<0.05 denotes a difference of pre-exercise between AM and PM trials. †P<0.05 denotes an interaction between AM and PM trials. ‡ P<0.05 denotes a main effect of trial between AM and PM trials.

Environmental conditions

In indoor environmental conditions, Ta (1−β = 0.97; d = 2.23) and Tg (1−β = 0.88; d = 1.74) were lower and RH (1−β = 0.66; d = 1.27) was higher on AM than PM trial (Table 1). In outdoor environmental conditions, absolute humidity (1−β = 0.96; d = 2.15) and solar radiation (1−β = 1.00; d = 3.19) were higher on AM than PM trial (Table 1).

Table 1

Indoor (Judo facility) and outdoor environmental conditions during each trial.

			Time				Mean ± SD	p value
	0	30	60	90	120	150
Indoor environment
Ta, °C
AM	32.0	32.4	32.8	33.0	33.0	33.1	32.7 ± 0.4	0.008
PM	35.5	35.3	34.8	34.1	34.0	32.4	34.4 ± 1.0
RH, %
AM	64	62	61	62	61	59	61 ± 2	0.037
PM	60	52	52	58	56	62	57 ± 4
AH, g·m−3
AM	21.7	21.4	21.5	22.1	21.6	21.2	21.6 ± 0.3	0.857
PM	24.4	20.9	20.4	21.9	21.1	21.4	21.7 ± 1.3
AV, km·h−1
AM	2.5	2.5	2.5	2.5	2.5	2.5	2.5 ± 0.0	1.000
PM	2.5	2.5	2.5	2.5	2.5	2.5	2.5 ± 0.0
WBGT, °C
AM	28.8	28.9	29.0	29.3	29.1	29.4	29.1 ± 0.2	0.074
PM	31.6	30.1	29.7	30.0	29.5	28.8	29.9 ± 0.8
Tg, °C
AM	34.5	35.0	35.0	34.9	35.1	36.6	35.2 ± 0.7	0.021
PM	38.3	37.5	37.2	36.8	36.4	34.6	36.8 ± 1.1
Tr, °C
AM	38.7	39.5	38.9	38.0	38.6	42.4	39.4 ± 1.4	0.114
PM	42.8	41.4	41.2	41.4	40.4	38.2	40.9 ± 1.4
Outdoor environment
Ta, °C
AM	31.9	31.9	32.6	32.9	33.0	33.6	32.7 ± 0.6	0.119
PM	33.5	32.9	31.5	31.0	30.7	30.2	31.6 ± 1.2
RH, %
AM	58	58	57	58	58	60	58.2 ± 0.9	0.416
PM	53	55	58	58	59	60	57.2 ± 2.4
AH, g·m−3
AM	19.5	19.5	19.9	20.6	20.7	22.1	20.4 ± 0.9	0.008
PM	19.4	19.5	19.1	18.6	18.6	18.4	18.9 ± 0.4
AV, km·h−1
AM	3.0	5.0	5.0	2.0	10.0	7.0	5.3 ± 2.6	0.469
PM	7.0	6.0	4.5	4.0	2.0	2.0	4.3 ± 1.9
WBGT, °C
AM	29.0	29.3	29.8	30.2	30.3	31.2	30.0 ± 0.7	0.147
PM	31.0	30.3	28.6	28.2	28.4	27.7	29.0 ± 1.2
Tg, °C
AM	42.0	42.5	43.0	43.5	43.8	44.8	43.3 ± 0.9	0.058
PM	45.0	43.2	38.5	38.1	37.2	35.5	39.6 ± 3.4
Tr, °C
AM	58.7	65.5	65.6	57.3	77.3	73.2	66.3 ± 7.2	0.124
PM	74.1	67.8	53.9	52.7	46.4	43.1	56.3 ± 11.1
SR, W·m−2
AM	860	920	930	1020	1060	1100	982 ± 85	<0.001
PM	810	510	300	220	160	110	352 ± 242

Ta, ambient temperature. RH, relative humidity. AH, absolute himidity. AV, air velocity

WBGT, wet-bulb globe temperature. Tg, black globe temperature. Tr, mean radiant temperature. SR, solar radiation.

In AM trial, higher RH (P<0.05; 1−β = 0.90; d = 1.81) and absolute humidity (P<0.05; 1−β = 0.89; d = 1.79) and lower WBGT (P<0.01; 1−β = 0.88; d = 1.75), Tg (P<0.001; 1−β = 1.00; d = 10.05) and Tr (P<0.001; 1−β = 1.00; d = 5.19) were apparent on the indoor than outdoor environmental conditions. In PM trial, higher Ta (P<0.001; 1−β = 0.99; d = 2.54), absolute humidity (P<0.01; 1−β = 1.00; d = 2.91) and WBGT (P<0.05; 1−β = 0.41; d = 0.88) and lower Tr (P<0.05; 1−β = 0.93; d = 1.95) were observed on the indoor than outdoor environmental conditions.

Body temperature responses

There was a trial by time interaction effect for Tty (P<0.05; 1−β = 0.82), but post hoc analysis revealed no difference at any time point between trials (all P>0.05; Fig 2A). Also, no main effect of trial was observed in Tty (P = 0.137). Although no interaction (P = 0.065) was shown in Tsk between trials, there was a main effect of trial in Tsk (P<0.05; 1−β = 0.53) which was higher on AM than PM trial (P<0.05; d = 0.22: Fig 2B).

Heart rate response

A trial by time interaction effect was detected for HR (P<0.05; 1−β = 0.91), but with post hoc adjustment there was no difference at any time point between trials (all P>0.05; Fig 2C). The percentage of HRmax (% HRmax) at 60, 120 and 150 min was 67±6%, 67±6% and 55±3% in AM trial and 72±7%, 63±4% and 57±7% in PM trial. There was a trial by time interaction effect for % HRmax (P<0.05; 1−β = 0.87), but post hoc analysis revealed no difference at any time point between trials (all P>0.05). The average HR during exercise was not different between trials (AM 63±4% HRmax, PM 64±5% HRmax; P = 0.680).

Heat loss responses

DHL (AM 5.3 W·m−2, PM −7.0 W·m−2; d = 7.79), EHL (AM 104.0 W·m−2, PM 97.9 W·m−2; d = 1.92) and THL (AM 109.3 W·m−2, PM 90.9 W·m−2; d = 3.89) were greater on AM than PM trial (all P<0.001; all 1−β = 1.00; Fig 3).

Fig 3

Responses of dry (DHL), evaporative (EHL) and total (THL) heat losses at the skin during exercise.

*P<0.001 denotes a difference between AM and PM trials.

Body fluid balance

There were no differences between trials in the volume of water ingested (AM 2254±718 mL; PM 2269±740 mL: P = 0.905), body mass loss (AM 1.2±0.6%; PM 1.3±0.9%: P = 0.565), total sweat loss (AM 3.1±0.8 kg; PM 3.1±0.7 kg: P = 0.509) and sweat rate (AM 1.23±0.30 L/h; PM 1.26±0.27 L/h: P = 0.481).

Perceptual responses

A trial by time interaction effect was shown for TS (P<0.05), but post hoc analysis revealed no difference at any time point between trials (all P>0.05; Fig 4A). Also, there was no main effect of trial in TS (P = 0.137). There was no interaction (P = 0.214) and main effect of trial (P = 0.089) in RPE, although a tendency was observed in a main effect of trial (Fig 4B).

Fig 4

Changes in thermal sensation (TS; A) and rating of perceived exertion (RPE; B) during exercise. *P<0.05 denotes an interaction between AM and PM trials.

Relationship between the changes in Tty, Tsk and HR and in environmental conditions

The changes in Tty was not correlated with the changes in environmental conditions in both trials. The changes in Tsk and HR in PM trial was strongly correlated with the changes in Ta, Tg, WBGT and Tr in the indoor environment and Tg, WBGT, Tr and solar radiation in the outdoor environment (Table 2). Also, the changes in HR in PM trial was moderately correlated with the changes in Ta in the outdoor environment.

Table 2

Spearman’ s rank correlation coefficianet (rs) between the changes in mean skin temperature (ΔTsk) and heart rate (ΔHR) in each participant and the changes in indoor and outdoor environmental conditions at 60, 120 and 150 min.

		Indoor					Outdoor
	ΔTa	ΔWBGT	ΔTg	ΔTr	ΔTa	ΔWBGT	ΔTg	ΔTr	ΔSR
ΔTsk
AM
rs	0.28	0.28	0.28	0.28	0.28	0.24	0.28	0.28	0.28
p value	n.s.	n.s.	n.s.	n.s.	n.s.	n.s.	n.s.	n.s.	n.s.
PM
rs	0.74	0.74	0.74	0.74	0.08	0.74	0.74	0.74	0.74
p value	<0.001	<0.001	<0.001	<0.001	n.s.	<0.001	<0.001	<0.001	<0.001
ΔHR
AM
rs	0.33	0.33	0.33	0.33	0.33	0.28	0.33	0.33	0.33
p value	n.s.	n.s.	n.s.	n.s.	n.s.	n.s.	n.s.	n.s.	n.s.
PM
rs	0.77	0.77	0.77	0.77	0.52	0.77	0.77	0.77	0.77
p value	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001

Ta, ambient temperature. WBGT, wet-bulb globe temperature. Tg, black globe temperature.

Tr, mean radiant temperature. SR, solar radiation.

Discussion

The current results demonstrated a higher Tsk in AM than PM trial (Fig 2B), despite greater DHL and EHL in AM than PM trial (Fig 3) with no differences between trials in hydration status. Tty and HR showed a trial by time interaction effect with no differences at any time point between trials (Fig 2A and 2C), indicating that these were relatively higher in PM than AM trial at the early stages of training but in AM than PM trial at the later stages of training. A novel finding in this study is that there is a greater thermoregulatory strain in the morning from 09:00 h than in the late afternoon from 16:00 h during 2.5-h regular judo training in a judo training facility without air conditioning in the heat of summer. This finding is associated with the progressive increase in indoor and outdoor heat stresses in the morning compared with the progressive decrease in indoor and outdoor heat stresses in the late afternoon. Therefore, our experimental hypothesis was confirmed. These findings are consistent with that of Otani and colleagues which involved 3-h moderate-intensity baseball training [1] and 2-h high-intensity football training [2] in high school athletes in the heat outdoors under a clear sky. As concluded in the previous studies [1, 2], the present study indicates that an increase in indoor heat stress during AM trial may cause a greater thermoregulatory strain than a decrease in indoor heat stress during PM trial, regardless of a smaller indoor heat stress in AM than PM trial and no solar radiation effect on both trials. Hence, the current study supports the previous studies [1, 2] and the risk for developing exertional heat-related illness during exercise may be relatively higher in the morning from 09:00 h than in the late afternoon from 16:00 h when 2.5-h regular judo training is performed in a judo training facility without air conditioning on a clear day in the heat of summer.

Regarding the relationships between indoor heat stress and physiological responses in no air conditioning facility during regular judo training in the summer, only one study of Revera-Brawn & Félix-Dávila [7] has reported the changes in hydration status in adolescent judokas during 90 min judo training in the afternoon from 15:30 h in a temperate environment (29.5°C Ta). Their study [7] showed that body mass loss, sweat rate and the volume of water ingested during the training were 1.9±0.5%, 0.8±0.3 L/h and 257±246 mL, respectively. These results indicate much greater body mass loss and an excessively lower sweat rate compared with the present results. These disagreements may exist due to the low volume of water ingested and an about 3–5°C lower Ta in the previous study [7] compared to the current study. Moreover, no information about exercise intensity was reported in the previous study [7]. Besides, only one study [20] reported the changes in Tty during regular judo training whilst wearing a cooling vest could have attenuated a greater increase in Tty during 65 min regular judo training and 10 min post-training recovery. The authors reported that the temperature was 27°C Ta at the beginning of training but they did not state the location where the temperature was measured (indoor or outdoor) and a presence of an air conditioner in the facility [20]. Considering that judo is the most popular combat sport in the world as well as Japanese junior high and high schools, more research is required to evaluate the influence of regular judo training in the heat on the risk of exertional heat-related illness.

In the present study, participants commenced exercise in a judo facility at high WBGT of 28.8°C and 31.6°C at 09:00 h (AM) and 16:00 h (PM), respectively (Table 1), which corresponds to an extreme risk category (≥28°C) for exertional heat-related illness [21]. WBGT kept increasing in AM trial and continued decreasing in PM trial, and WBGT was 29.4°C and 28.8°C at the end of exercise in AM (11:30 h) and PM (18:30 h) trials, respectively (Table 1). These indicate that participants were continuously exposed to heat strain that is regarded as extreme risk for exertional heat-related illness in both trials throughout the training. Indoor heat stress of Ta, Tg and Tr also continued to increase during AM trial but they decreased continuously during PM trial that indoor heat stress at the early stages of training was greater in PM than AM trial but the stress at the later stages of training was greater in AM than PM trial (Table 1). Consequently, there was a smaller indoor heat stress with significantly lower Ta and Tg during exercise in AM than PM trial (Table 1). These changes were well linked to the changes in outdoor heat stress because Ta, WBGT, Tg and Tr in outdoors also kept increasing during AM trial and decreasing during PM trial. This study therefore clearly indicates that indoor heat stress increases with increasing outdoor heat stress in the morning or decreases with decreasing outdoor heat stress in the afternoon in a judo training facility without air conditioning on a clear day in the heat of summer. These changes led to greater outdoor than indoor heat stress during the morning in AM trial and greater indoor than outdoor heat stress during the late afternoon in PM trial. This observation is consistent with the common findings of the architectural studies about the diurnal relationships between indoor and outdoor heat stress in a building during the summer [22].

In agreement with the previous studies during outdoor exercise [1, 2], the current study detected a greater thermoregulatory strain during indoor exercise in AM trial than in PM trial. Average HRmax during exercise was 63±4% in AM trial and 64±5% in PM trial which are corresponding to moderate-intensity exercise [23] and similar to the study that was conducted in 3-h moderate-intensity baseball training [1] but lower than the study that was conducted in 2-h high-intensity football training [2]. These studies reported higher Tty and HR [1, 2] and a higher Tsk [1] in the morning than in the afternoon trial. In this study, Tsk was higher but heat-loss responses of both DHL and EHL were greater in AM than PM trial (Figs 2B and 3). This means a greater heat-gain during exercise in AM than PM trial. Tsk at 60 and 120 min of exercise was exceeding 35°C during both trials which is consistent with [2] but higher than [1] the previous studies. It has been known that Tsk of greater than 35°C can evoke the early onset of fatigue in a hot environment [24, 25]. Although the present study did not measure exercise performance, the high Tsk may have caused an early decline in judo performance in both trials. Given that the changes in Tsk in PM trial was related to the changes in Ta, Tg, WBGT and Tr in the indoor environment (Table 2), a decrease in indoor heat stress in the late afternoon would attenuate a greater increase in Tsk in PM trial and which is in line with Otani et al. [1]. Hence, although indoor heat stress was less in AM than PM trial, the progressive increase in indoor and outdoor heat stresses in AM trial may have led to a higher Tsk in AM trial compared with PM trial.

The studies of Otani et al. [1, 2] observed an interaction with higher Tty and HR at the later stages of training in the morning than the afternoon trial in the heat outdoors under a clear sky, whereas the current study showed only an interaction with no differences at any time point between trials in Tty and HR (Fig 2A and 2C). Given that the current study detected about 3–8°C lower Tg and 12–37°C lower Tr than the studies of Otani et al. [1, 2], the impact of solar radiation may have caused the differences in the diurnal impact on Tty and HR responses between the previous and current studies. In this study, the changes in indoor heat stress as measured by Ta, WBGT, Tg and Tr, Tty and HR showed similar responses where the values were higher in PM than AM trial at the early stages of training, whilst higher in AM than PM trial at the later stages of training. Therefore, it is possible that the changes in Tty and HR responses are easily influenced by the changes in indoor heat stress during indoor exercise in no air conditioning facility in the heat. This may be responsible for the disagreements in the time-of-day influence on Tty and HR responses between the past [1, 2] and current studies.

Perceived thermal stress (i.e. TS) was greater in PM than AM trial at the early stages of training and in AM than PM trial at the later stages of training, even though perceived fatigue (i.e. RPE) was not different between trials (Fig 4). Previous studies demonstrated that RPE and TS responses were almost similar between the morning and afternoon trials during outdoor exercise, although Tty, Tsk and HR were higher in the morning than the afternoon trial [1, 2]. In the present study, RPE response was consistent but TS response was inconsistent with the previous studies [1, 2]. These results indicate that perceived fatigue during exercise in the heat may not be influenced by the time-of-day and location (indoor or outdoor) when the same training is performed. Meanwhile, Schlader & Vargas [26] reported that central thermoreceptor activation (i.e. ΔTcore) rather than peripheral thermoreceptor activation (i.e. Δskin temperature) may play a role in perceived thermal stress to exercise in a moderate environment. Although the current study was conducted in a hot environment, statistical analyses revealed the similar changes during exercise between TS and Tty rather than Tsk. Moreover, given that the changes in TS were also similar to the changes in HR, a higher TS response in PM than AM trial at the early stages of training and in AM than PM trial at the later stages of training would be in accordance with the changes in indoor heat stress as the same responses were observed from Tty and HR. Based on these observations, the chronobiological effect on perceived thermal stress during indoor exercise in the heat may be associated with a combination of the changes in Tcore and the time-of-day variations in indoor heat stress. Since no studies have systematically examined this effect in any sports including judo, further investigations are required.

The present study is not without limitations. This study used Tty to evaluate Tcore. Nevertheless, previous studies reported that rectal temperature relates to [12] or does not relate to [27] Tty during exercise in the heat. Future research therefore should employ rectal temperature to engage a greater validity and reliability in study regarding the risk of exertional heat-related illness during exercise in the heat of summer. Meanwhile, the current study estimated fcl, Rcl and Re,cl of judo uniform as 1.23, 0.119 W·(m2·°C)−1 and 0.022 W·(m2·kPa)−1, respectively, using that of the similar clothing reported. However, we cannot confirm that whether these estimations are within the acceptable difference for true values. This study observed high Tsk of greater than 35°C in both trials that might be accompanied by strong heat which could have accumulated inside the judo uniform. To further elucidate the effects of wearing a judo uniform on heat-gain and -loss responses during judo training in the heat, exact clo values for judo ensemble needs to be established. The present study was conducted in a completely sunny condition. This means that outdoor heat stress continued to increase during the morning and decrease during the afternoon as solar elevation angle rises and falls [28]. That would result in a stable increase of indoor heat stress during AM trial and a stable decrease of indoor heat stress during PM trial in a judo training facility without air conditioning. If the present study was conducted under cloudy conditions, thermoregulatory responses could have been unstable because outdoor and indoor heat stress may not have uniformly increased or decreased. Given this assumption, future study needs to perform the same experiments as the present study under thin or thick cloud conditions.

Conclusions

We conclude that thermoregulatory strain is greater in the morning from 09:00 h than in the late afternoon from 16:00 h in Japanese high school judokas during 2.5-h regular judo training in a judo training facility without air conditioning on a clear day in the heat of summer. This is attributed to a higher Tsk relative to greater DHL and EHL in the morning compared with the late afternoon during exercise, although Tty, HR and TS at the early stages of training were higher in the late afternoon than the morning but these at the later stages of training were higher in the morning than in the late afternoon. These findings would be owing to a progressive increase in indoor heat stress with increasing outdoor heat stress in the morning compared with a decrease in indoor heat stress with decreasing outdoor heat stress in the late afternoon when it is a clear day. These observations suggest that judo training in a judo training facility without air conditioning on a clear day in the heat of summer may be at a relatively higher risk for developing exertional heat-related illness in the morning from 09:00 h when the starting WBGT is about 29°C compared with the late afternoon from 16:00 h. Therefore, we suggest conducting judo training in the afternoon from 16:00 h to minimise the risk of developing an exertional heat-related illness in the heat on a clear day, even if the starting WBGT is about 31°C. While an exertional heat-related illness is commonly considered as a risk of outdoor activity, athletes and coaches of indoor sports should recognize that activities in indoor facility do not exempt them from heat stress. Proactive heat mitigation strategies applied in other outdoor sports (e.g. adjustment of work to rest ratio, individualized hydration plan) should also be implemented in Judo and other high intensity indoor sports. As WBGT was exceeding 29°C from the end of AM trial (11:30 h) to the start of PM trial (16:00 h), judo training in such environmental conditions should be avoided to eliminate the mortality and morbidity of heat-related illnesses.

(DOCX)

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12 Aug 2020

PONE-D-20-11199

Greater thermoregulatory strain in the morning than late afternoon during judo training in the heat of summer

PLOS ONE

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Reviewer #1: The present paper "Greater thermoregulatory strain in the morning than late afternoon during judo training in the heat of summer" has important methodological problems that lead me to suggest an important review by the authors.

General comments

Reading the paper is difficult, so authors are recommended to use a language review service. I have some doubts about the adequacy of the statistical analyzes used to address the question that arises. In addition, there are certain inaccuracies in the method that must be addressed in order to understand what was done and how it was done. The discussion should be re-writed according to the results obtained after the employment of correct analysis and more about physiological implications for judo training has to be addressed.

Specific comments

Page 9, lines 80-81. This is possible because most judo halls have 81 no air-conditioner owing to its high running costs

Reviewer: please correct English.

Page 9, lines 86. endurance performance

Reviewer: I suggest to add that "judo has high-density efforts" what increases internal temperature (cites).

Page 9, lines 88 and 90. "high body mass index"

Reviewer: the reference is a position statement that cites another position statement that cites references of miners workers. I suggest to seek for a reference on athletes exercising in the heat, and authors should ensure specify if it is BMI or fat mass the cause of worse thermoregulatory capacity.

Page 10, line 121. "The hall is one story,..."

Reviewer: I do not understand what the authors mean.

Page 11, lines 125-126. "...PM trial was conducted first and AM trial was carried out 2 days later..."

Reviewer: why not were the sessions balanced?

Page 11, line 129. "This judo ensemble was 2.5 kg of total weight."

Reviewer: please if the authors consider necessary to report that information, the mean weight and SD should be provided, or minimum and maximum, since judokas had different weight categories are expected to have different sizes of judo is with different extra-weights.

Page 11, lines 132-137. "...including 0.18 clo of short sleeve..."

Reviewer: please define "clo" and it would help to introduce the units expressed in the paragraph to ease the unfamiliar words to be understood by the reader.

Page 11, lines 138-140. "Participants entered a laboratory which is close to the judo hall after a 2 h fast in each trial, other than the ingestion of plain water 30 min before the start of the trial. Upon arrival participants first emptied their bladder and nude body mass was measured to the nearest 10 g"

Reviewer: please re-phrase this sentence.

Page 11, lines 143-155.

Reviewer: the authors must correct the writing style since it is difficult to understand. Furthermore, the authors have to express constantly abbreviations.

Page 12, lines 165. perceived exertion (RPE)

Reviewer: the authors must specify what scale and question were employed to measure perceived exertion/effort, I encourage the review of Halperin & Emmanuel. Sports Med. 2020.

Page 12, lines 166-167. "Skin temperatures and HR were also recorded every 60 min and the end of the training using a thermometer..." - Please re-phrase, it is not clear when the measurement was done. A figure representing the schedule of measurements is encouraged.

Page 12-13. Calculations

Reviewer: I suggest to include this material as supplementary material.

Page 14, line 229-230. "...using Friedman’s two-way ANOVA."

Reviewer: I recommend the employment of the package nparLD (Noguchi et al. Journal of statistical software. 2012) since it allows the study of the interaction (what seems to be the aim of the study) unlike the Friedman's test.

Page 14, lines 231-232."...a two-way (2 [time-of-day] × 3 to 4 [time]) repeated measures ANOVA."

Reviewer: please express the ANOVA factors in a correct way, moreover, the number of measurement does not coincide with the represented in table 1.

Page 14, line 234. "...dependent (indoor vs. outdoor) samples t-test"

Reviewer: please define correctly the dependent variable and if the objective is to compare the time of the day and place of measurement (indoor vs outdoor), as it seems, an ANOVA test is more suitable.

Page 15, lines 247-257.

Reviewer: I really do not understand how the authors made the statistical analysis and I have my concerns about the interpretation of the results according to the statistical analysis described in the methods section.

Page 16, lines 273-274. Average HR during exercise was not different between trials (AM 63±4% HRmax, PM 64±5% 274 HRmax; P=0.680).

Reviewer: it seems that HR is from the entire session, an analysis of the more demanding task would clarify better the internal load imposed on the judokas and it could facilitate the interpretation of the possible effects of time of the day and indoor temperature on the cardiovascular effort of the athletes. An important point to consider is that likely the more physically demanding part of the sessions was performed in the part of the session with higher indoor temperature in AM and in the part of the sessions with lower indoor temperature in PM. Thus, an analysis of HR measured in relation to the task performed is required to interpret the data.

Page 17, lines 311-314. "A novel finding in this study is that there is a greater thermoregulatory strain in the morning from 09:00 h than in the late afternoon from 16:00 h during 2.5-h regular judo training in no air conditioning judo hall in the heat of summer irrespective of environmental heat stress."

Reviewer: the conclusion of the study has bias because the evolution of temperature has to be analysed regarding with the demands of the judo task, since the cumulative effect of the increase of temperature and higher efforts can influence the physiological effects on judocas.

Page 18, lines 364-365. "Average HRmax during exercise was 63±4% in AM trial and 64±5% in PM trial which are corresponding to moderate-intensity exercise [27] and similar to [1] but lower than [2] the previous..."

Reviewer: to compare data between studies it would be necessary have into account the task performed by the athletes.

Reviewer #2: The manuscript presents interesting data from apparently well-conducted investigation examining the influence of AM versus PM training sessions; however, the document needs substantial language editing prior to further consideration for publication. Some additional comments and suggestions are provided below.

Consider an alternative to “no air conditioning judo hall” throughout the paper; perhaps “judo training facility without air conditioning.”

The following sentence used in the abstract and elsewhere is confusing: “showing relatively higher responses in these variables in PM than AM and in AM than PM at the early and the later stages of training, respectively.” Perhaps the following would be more clear: “showing relatively higher responses in these variables in the PM compared to the AM during the early stages of training and in the AM compared to the PM during the later stages of training.”

Some of the following additional relevant details for the participants and environment may be useful:

What is the training age or the number of years of training for the partcipants?

Did they typically engage in the type of judo training examined during the study in both the AM and PM or was one time reserved for other types of training (running, lifting weights, newaza, etc.)?

How much time had elapsed since the previous training session?

Did the athletes start the training in a dry judogi?

Regarding the different finding for TS and RPE, is it possible that the judo athletes self-regulate to adjust to an expected or typical RPE while still acknowledging differences in TS?

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Reviewer #1: No

Reviewer #2: No

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1 Sep 2020

Response to Reviewer 1

We are grateful to reviewer for the critical comments and useful suggestions that have helped us to improve our manuscript. As indicated in the responses that follow, we have taken all these comments and suggestions into account in the revised version of our manuscript.

Comment#1:

General comments

Reading the paper is difficult, so authors are recommended to use a language review service. I have some doubts about the adequacy of the statistical analyzes used to address the question that arises. In addition, there are certain inaccuracies in the method that must be addressed in order to understand what was done and how it was done. The discussion should be re-writed according to the results obtained after the employment of correct analysis and more about physiological implications for judo training has to be addressed.

Response to Comment#1:

Thank you for these comments. This paper has been proofread by a native English speaker again. The changes are shown in red in the revised version of text (clean copy). We hope that our comments below are relevant to the response to the reviewer’s comments.

Comment#2:

Specific comments

Page 9, lines 80-81. This is possible because most judo halls have 81 no air-conditioner owing to its high running costs

Reviewer: please correct English.

Response to Comment#2:

We agree with this comment. In relation to another reviewer’s comment, we would like to replace this sentence “This is possibly because most judo halls have no air-conditioner owing to its high running costs.” with “This is possibly due to luck of air conditioning in most judo facilities owing to its high running costs.”.

Comment#3:

Page 9, lines 86. endurance performance

Reviewer: I suggest to add that "judo has high-density efforts" what increases internal temperature (cites).

Response to Comment#3:

Thank you for this suggestion. We have added “has high-density efforts and” to this sentence in line 85 in the revised version of text (clean copy).

Comment#4:

Page 9, lines 88 and 90. "high body mass index"

Reviewer: the reference is a position statement that cites another position statement that cites references of miners workers. I suggest to seek for a reference on athletes exercising in the heat, and authors should ensure specify if it is BMI or fat mass the cause of worse thermoregulatory capacity.

Response to Comment#4:

This reference (Casa et al. J Athl Train. 2015) cited two references about the effects of the risk in high body mass index on heat-related illnesses. One is the study of Cleary (J Sport Rehabil. 2007;16(3):204–214), the other is the study of Chung and Pin (Mil Med. 1996;161(12):739–742). We are afraid that we confirmed both studies analysing the data during exercise. Therefore, we would like to use the reference of Casa et al. as it is.

Comment#5:

Page 10, line 121. "The hall is one story,..."

Reviewer: I do not understand what the authors mean.

Response to Comment#5:

In relation to another reviewer’s comment, we would like to replace this sentence “The hall is one story,…” with “The judo facility is a one-story building with a floor space of 225 m2 (15 m × 15m).”.

Comment#6:

Page 11, lines 125-126. "...PM trial was conducted first and AM trial was carried out 2 days later..."

Reviewer: why not were the sessions balanced?

Response to Comment#6:

We understand the reviewer’s comment. However, to keep constant environmental conditions during the trial, we had to carry out each trial in all participants together. Therefore, we had no choice but to carry out first either AM trial or PM trial.

Comment#7:

Page 11, line 129. "This judo ensemble was 2.5 kg of total weight."

Reviewer: please if the authors consider necessary to report that information, the mean weight and SD should be provided, or minimum and maximum, since judokas had different weight categories are expected to have different sizes of judo is with different extra-weights.

Response to Comment#7:

Thank you for this suggestion. We have replaced this sentence “This judo ensemble was 2.5 kg of total weight.” with “The judo ensemble was 2.5±0.1kg of total weight.”.

Comment#8:

Page 11, lines 132-137. "...including 0.18 clo of short sleeve..."

Reviewer: please define "clo" and it would help to introduce the units expressed in the paragraph to ease the unfamiliar words to be understood by the reader.

Response to Comment#8:

We agree with this comment. We have added the following sentence “A clo is a unit of thermal insulation for clothing: one clo can be defined as the amount of insulation that allows the transfer of 1 W·m−2 with a temperature gradient of 0.155°C between two surfaces (0.18°C·m2·h·kcal−1).” to line 136-138 in the revised version of text (clean copy).

Comment#9:

Page 11, lines 138-140. "Participants entered a laboratory which is close to the judo hall after a 2 h fast in each trial, other than the ingestion of plain water 30 min before the start of the trial. Upon arrival participants first emptied their bladder and nude body mass was measured to the nearest 10 g"

Reviewer: please re-phrase this sentence.

Response to Comment#9:

We agree with this comment. We have changed these sentences to “Participants entered a laboratory which was close to the judo facility after a 2 h fast in each trial with the exception of plain water, which was allowed until 30 min before the start of the trial. Upon arrival, participants first emptied their bladder and thereafter nude body mass was measured to the nearest 10 g”.

Comment#10:

Page 11, lines 143-155.

Reviewer: the authors must correct the writing style since it is difficult to understand. Furthermore, the authors have to express constantly abbreviations.

Response to Comment#10:

We agree with this comment. We have changed these sentences to

“Surface skin temperature thermistor probes (ITP082-25, Nikkiso-Therm Co., Ltd., Musashino, Tokyo, Japan) were attached to four sites (chest, upper arm, thigh and calf) under the clothing without preventing range of motion. A weighted average of chest (0.3), upper arm (0.3), thigh (0.2) and calf (0.2) skin temperatures was used to calculate mean skin temperature (Tsk) [10]. Gastrointestinal thermometry has been shown to be a valuable device for core temperature (Tcore) assessment in the field and athletics settings [11]. However, the current study measured an infrared tympanic temperature (Tty) to estimate Tcore due to the restriction from pharmaceutical affairs law in Japan using gastrointestinal thermometry. Tty was measured using an infrared tympanic thermometer (GeniusTM 2, Covidien, Mansfield, MA, USA). In each measurement, two consecutive readings were obtained. All Tty measurements were taken by a single operator, using the recommended technique [12]. To avoid the increased effects of increasing Ta on Tty in the heat [13], the thermometer was stored inside a cooling box during the trial. The temperature inside this box was maintained by ice packs at about 25°C. Thermal sensation (TS) was measured using a 9-point scale [14]. All pre-exercise measurements were carried out in the laboratory in a temperate environment (25-27°C Ta) because prior heat stress exposure may increase thermoregulatory strain during subsequent exercise-heat stress in the morning than in the afternoon [15].”

In accordance with this change, we would like to add the following sentences to line 3-4 in supporting information (S1 Methods-Calculations) in relation to Comment#13, “Tsk was calculated using the following equation [10]: Tsk = 0.3×chest + 0.3×upper arm + 0.2×thigh + 0.2×calf [ºC].”.

Comment#11:

Page 12, lines 165. perceived exertion (RPE)

Reviewer: the authors must specify what scale and question were employed to measure perceived exertion/effort, I encourage the review of Halperin & Emmanuel. Sports Med. 2020.

Response to Comment#11:

Thank you for this comment and introducing a good manuscript. In accordance with this, we have replaced this sentence “During the sessions, Tty, TS and rating of perceived exertion (RPE) [17] were assessed every 60 min and the end of the training.” with “During the sessions, Tty and TS were assessed every 60 min and the end of the training. To determine whole-body perception of effort, rating of perceived exertion (RPE) was assessed every 60 min and the end of the training using the 6-20 RPE scale [17].”.

Comment#12:

Page 12, lines 166-167. "Skin temperatures and HR were also recorded every 60 min and the end of the training using a thermometer..." - Please re-phrase, it is not clear when the measurement was done. A figure representing the schedule of measurements is encouraged.

Response to Comment#12:

We agree with the reviewer’s comment. we have replaced the following sentences “Skin temperatures and HR were also recorded every 60 min and the end of the training using a thermometer (N543R, Nikkiso-Therm Co., Ltd., Musashino, Tokyo, Japan) and HR monitor (A370, Polar Electro, Kempele, Finland), respectively.” with “Skin temperatures (thermometer N543R, Nikkiso-Therm Co., Ltd., Musashino, Tokyo, Japan) and HR (HR monitor A370, Polar Electro, Kempele, Finland) were also recorded every 60 min and the end of the training (Fig 1)”.

Moreover, in relation to this comment and another reviewer’s comment#4, we would like to add the experimental protocol as Figure 1. Therefore, we would like to replace “Fig 1” with “Fig 2”, “Fig 2” with “Fig 3”, and “Fig 3” with “Fig 4” throughout the text. Moreover, we would like to add the following figure legends, “Fig 1. Schematic representation of the experimental protocol. Tty, infrared tympanic temperature; HR, heart rate; TS, thermal sensation; RPE, rating of perceived exertion.”.

Comment#13:

Page 12-13. Calculations

Reviewer: I suggest to include this material as supplementary material.

Response to Comment#13:

We agree with the reviewer’s suggestion. We have transferred the sentences from line 185 to line 223 to the supplementary material. In accordance with this, we have added the following sentence to line 197-199 in the revised version of text (clean copy), “The equations of Tsk, mean radiant temperature (Tr), dry or sensible heat loss (DHL), evaporative heat loss (EHL), total heat loss (THL), absolute humidity and total sweat loss are included in supporting information (S1 Methods-Calculations).”.

Comment#14:

Page 14, line 229-230. "...using Friedman’s two-way ANOVA."

Reviewer: I recommend the employment of the package nparLD (Noguchi et al. Journal of statistical software. 2012) since it allows the study of the interaction (what seems to be the aim of the study) unlike the Friedman's test.

Response to Comment#14:

We appreciate this suggestion. In accordance with this, we have re-calculated thermal sensation (TS) using the R package nparLD by helping Dr. Jos Feys, University of Leuven. However, the results of TS were not substantially different that in the original version of the text. In relation to this, we have changed the following points:

1. Removed the following sentence from line 226-227 in the original version of text, “The IBM SPSS (version 21; IBM Corp., Armonk, N.Y., USA) was used for all statistical analyses.”

2. Replaced the following sentence in line 229-230 in the original version of text, “Non-parametric data (TS) were analysed using Friedman’s two-way ANOVA.” with “Non-parametric data (TS) were analysed using R. TS was analysed using a two-way (time-of-day [two levels, i.e., AM and PM] × time [four levels, i.e., 0, 60, 120 and 150 min]) repeated measures ANOVA with the R package nparLD. Pair-wise differences between trials were evaluated using the Kruskal-Wallis test with the Wilcoxon rank sum test.”

3. Added the following sentence to line 205-206 in the revised version of text (clean copy), “statistical analyses of data were done in the IBM SPSS (version 21; IBM Corp., Armonk, N.Y., USA).”

4. Replaced the following sentence, line 230-231 in the original version of text, “, data collected once per trial were analysed using a one-way repeated measures ANOVA,” with “Data collected once per trial were analysed using a one-way repeated measures ANOVA,”

5. Replaced the following sentences, line 290-292 in the original version of text, “A trial by time interaction effect was shown for TS (P<0.05; 1−β=0.82), but post hoc analysis revealed no difference at any time point between trials (all P>0.05; Fig 3A). Also, there was no main effect of trial in TS (P=0.381).” with “A trial by time interaction effect was shown for TS (P<0.05), but post hoc analysis revealed no difference at any time point between trials (all P>0.05; Fig 4A). Also, there was no main effect of trial in TS (P=0.137).”.

6. Replaced the following sentence to Acknowledgements, line 459 in the original version of text, “The authors also thank, Eri Arimoto, Jiei Kusunoki and Ryutaro Tanaka for assistance.” with “The authors also thank Dr. Jos Feys, University of Leuven, for statistical analysis assistance, and Eri Arimoto, Jiei Kusunoki and Ryutaro Tanaka for assistance.”.

Comment#15:

Page 14, lines 231-232."...a two-way (2 [time-of-day] × 3 to 4 [time]) repeated measures ANOVA."

Reviewer: please express the ANOVA factors in a correct way, moreover, the number of measurement does not coincide with the represented in table 1.

Response to Comment#15:

We agree with this comment. We have replaced this sentence “using a two-way (2 [time-of-day] × 3 to 4 [time]) repeated measures ANOVA.” with “using a two-way (time-of-day [two levels, i.e., AM and PM] × time [three or four levels, i.e., 0, 60, 120 and 150 min]) repeated measures ANOVA.”.

The sampling interval of each environmental conditions data were expressed in line 176-182 in the original version of text. We would like to add the sampling interval of environmental conditions in Figure 1.

Comment#16:

Page 14, line 234. "...dependent (indoor vs. outdoor) samples t-test"

Reviewer: please define correctly the dependent variable and if the objective is to compare the time of the day and place of measurement (indoor vs outdoor), as it seems, an ANOVA test is more suitable.

Response to Comment#16:

We agree with the reviewer’s comment. We have replaced the following phrase, line 234-235, “...dependent (indoor vs. outdoor) samples t-test” with “…dependent (indoor AM vs. outdoor AM; indoor PM vs. outdoor PM) samples t-test”.

Meanwhile, given that indoor and outdoor environmental variables were measured at the same time and collected once per each sampling point in this study, these variables are need to analyse the dependent samples t-test between indoor and outdoor environments. An ANOVA test is suitable when there are more than three groups but is inappropriate between the two groups. By the way, when two groups are compared, the results of statistical analysis (the P value) are completely the same between the dependent sample t-test and the repeated measures ANOVA.

Comment#17:

Page 15, lines 247-257.

Reviewer: I really do not understand how the authors made the statistical analysis and I have my concerns about the interpretation of the results according to the statistical analysis described in the methods section.

Response to Comment#17:

We hope that our comments in Response to Comment#16 are relevant to the response to this comment.

Comment#18:

Page 16, lines 273-274. Average HR during exercise was not different between trials (AM 63±4% HRmax, PM 64±5% 274 HRmax; P=0.680).

Reviewer: it seems that HR is from the entire session, an analysis of the more demanding task would clarify better the internal load imposed on the judokas and it could facilitate the interpretation of the possible effects of time of the day and indoor temperature on the cardiovascular effort of the athletes. An important point to consider is that likely the more physically demanding part of the sessions was performed in the part of the session with higher indoor temperature in AM and in the part of the sessions with lower indoor temperature in PM. Thus, an analysis of HR measured in relation to the task performed is required to interpret the data.

Response to Comment#18:

We agree with this comment. We would like to add the following sentences to line 250-254 in the revised version of text (clean copy), “The percentage of HRmax (% HRmax) at 60, 120 and 150 min was 67±6%, 67±6% and 55±3% in AM trial and 72±7%, 63±4% and 57±7% in PM trial. There was a trial by time interaction effect for % HRmax (P<0.05; 1−β=0.87), but post hoc analysis revealed no difference at any time point between trials (all P>0.05).”.

Comment#19:

Page 17, lines 311-314. "A novel finding in this study is that there is a greater thermoregulatory strain in the morning from 09:00 h than in the late afternoon from 16:00 h during 2.5-h regular judo training in no air conditioning judo hall in the heat of summer irrespective of environmental heat stress."

Reviewer: the conclusion of the study has bias because the evolution of temperature has to be analysed regarding with the demands of the judo task, since the cumulative effect of the increase of temperature and higher efforts can influence the physiological effects on judocas.

Response to Comment#19:

We agree with this comment. We have changed this sentence to “A novel finding in this study is that there is a greater thermoregulatory strain in the morning from 09:00 h than in the late afternoon from 16:00 h during 2.5-h regular judo training in judo training facility without air conditioning in the heat of summer. This finding is associated with the progressive increase in indoor and outdoor heat stresses in the morning compared with the progressive decrease in indoor and outdoor heat stresses in the late afternoon.”

Comment#20:

Page 18, lines 364-365. "Average HRmax during exercise was 63±4% in AM trial and 64±5% in PM trial which are corresponding to moderate-intensity exercise [27] and similar to [1] but lower than [2] the previous..."

Reviewer: to compare data between studies it would be necessary have into account the task performed by the athletes.

Response to Comment#20:

We appreciate this suggestion. In accordance with this, we have changed this sentence to “Average HRmax during exercise was 63±4% in AM trial and 64±5% in PM trial which are corresponding to moderate-intensity exercise [27] and similar to the study that was conducted in 3-h moderate-intensity baseball training [1] but lower than the study that was conducted in 2-h high-intensity football training [2]”.

We are most grateful for your comments on our manuscript. We trust that the revised version of our manuscript is suitable for publication.

----------------------------------------------------------------------------------------------------

Response to Reviewer 2

We are grateful to reviewer for the critical comments and useful suggestions that have helped us to improve our manuscript. As indicated in the responses that follow, we have taken all these comments and suggestions into account in the revised version of our manuscript.

Comment#1:

Consider an alternative to “no air conditioning judo hall” throughout the paper; perhaps “judo training facility without air conditioning.”

Response to Comment#1:

We appreciate this suggestion. In accordance with this, we have replaced “no air conditioning judo hall” with “judo training facility without air conditioning” throughout the paper.

In relation to this, we have replaced “hall/halls” with “facility/facilities” throughout the paper.

Comment#2:

The following sentence used in the abstract and elsewhere is confusing: “showing relatively higher responses in these variables in PM than AM and in AM than PM at the early and the later stages of training, respectively.” Perhaps the following would be more clear: “showing relatively higher responses in these variables in the PM compared to the AM during the early stages of training and in the AM compared to the PM during the later stages of training.”

Response to Comment#2:

Thank you for this comment. We agree with this comment. We have replaced “showing relatively higher responses in these variables in PM than AM and in AM than PM at the early and the later stages of training, respectively” with “showing relatively higher responses in these variables in PM compared to AM during the early stages of training and in AM compared to PM during the later stages of training” in the Abstract.

Comment#3:

Some of the following additional relevant details for the participants and environment may be useful:

What is the training age or the number of years of training for the partcipants?

Response to Comment#3:

We agree with this comment. In accordance with this, we have added the following phrase “, years of training 6±2 y” to line 109 in the revised version of text (clean copy).

Comment#4:

Did they typically engage in the type of judo training examined during the study in both the AM and PM or was one time reserved for other types of training (running, lifting weights, newaza, etc.)?

Response to Comment#4:

We are sorry that our explanation about the type of judo training (Line 161-165 in the original version of text) was a little confusing. To clarify this and in relation to another reviewer’s comment#12, we would like to add the experimental protocol as Figure 1. In relation to this change, we would like to replace “Fig 1” with “Fig 2”, “Fig 2” with “Fig 3”, and “Fig 3” with “Fig 4” throughout the text. Moreover, we would like to add the following figure legends, “Fig 1. Schematic representation of the experimental protocol. Tty, infrared tympanic temperature; HR, heart rate; TS, thermal sensation; RPE, rating of perceived exertion.”.

Comment#5:

How much time had elapsed since the previous training session?

Response to Comment#5:

We agree with this comment. In accordance with this, we have added the following sentence to line 127-129 in the revised version of text (clean copy), “A normal training session took place two days before the first trial (PM trial) but no exercise was permitted during the 24 h prior to the trials.”.

Comment#6:

Did the athletes start the training in a dry judogi?

Response to Comment#6:

Yes, exactly. We have added the following sentence to line 163-164 in the revised version of text (clean copy), “Participants started the sessions in a dry judo uniform.”.

Comment#7:

Regarding the different finding for TS and RPE, is it possible that the judo athletes self-regulate to adjust to an expected or typical RPE while still acknowledging differences in TS?

Response to Comment#7:

We think that no differences in RPE between AM and PM trials may be accompanied by the same content of training in both trials, regardless of the differences in TS. However, as the reviewer have pointed out, it was possible that participants self-regulated their exercise intensity to prevent excessive fatigue, especially in the early stages of training.

We are most grateful for your comments on our manuscript. We trust that the revised version of our manuscript is suitable for publication.

Submitted filename: Response to Reviewer#1.docx

Click here for additional data file.

13 Oct 2020

PONE-D-20-11199R1

Greater thermoregulatory strain in the morning than late afternoon during judo training in the heat of summer

PLOS ONE

Dear Dr. Otani,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please carefully review the manuscript and correct the few grammatical errors.

Please specify the version of R.

Please define thoroughly HRmax.

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Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: No

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: I would like to congratulate the authors since they have made a great work adressing the reviwers comments and rise the paper to the standards to be published in Plosone.

Reviewer #2: Minor grammatical errors still exist throughout the text that should be easy enough to address with a thorough review.

Please specify the version of R.

An operational definition of HRmax is needed to provide context for the current results.

**********

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Reviewer #1: Yes: Eduardo Carballeira

Reviewer #2: No

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20 Oct 2020

Response to Reviewer 1

We are grateful to reviewer for the critical comments and useful suggestions that have helped us to improve our manuscript.

We are afraid that our statistical adviser (Dr. Jos Feys, University of Leuven) has pointed out that the Tukey multiple comparison tests rather than the Kruskal-Wallis test with the Wilcoxon rank sum test are a practical and powerful approach to multiple testing in this TS data. The results of statistical analysis in the TS data were not different the present results when using the Tukey multiple comparison tests. Therefore, we would like to replace the following sentence, line 205-206,

“Pair-wise differences between trials were evaluated using the Kruskal-Wallis test with the Wilcoxon rank sum test.”

with

“Pair-wise differences between trials were evaluated using the Tukey multiple comparison tests.”

We are most grateful for your comments on our manuscript. We trust that the second revised version of our manuscript is suitable for publication.

-----------------------------------------------------------------------------

Response to Reviewer 2

We are grateful to reviewer for the critical comments and useful suggestions that have helped us to improve our manuscript. As indicated in the responses that follow, we have taken all these comments and suggestions into account in the second revised version of our manuscript.

Comment#1:

Minor grammatical errors still exist throughout the text that should be easy enough to address with a

thorough review.

Response to Comment#1:

In accordance with the reviewer’s comment, this paper has been re-proofread by a native English speaker. The changes are shown in red in the revised version of text.

Comment#2:

Please specify the version of R.

Response to Comment#2:

We agree with this comment. To add the version of R, we have replaced the following sentences, line 203-205,

“Non-parametric data (TS) were analysed using R. TS was analysed using a two-way (time-of-day [two levels, i.e., AM and PM] × time [four levels, i.e., 0, 60, 120 and 150 min]) repeated measures ANOVA with the R package nparLD”

with

“Non-parametric data (TS) were analysed using R (version 4.0.2). TS was analysed using a two-way (time-of-day [two levels, i.e., AM and PM] × time [four levels, i.e., 0, 60, 120 and 150 min]) repeated measures ANOVA with the R package nparLD (version 2.1) for the LD-F2 design.”.

Comment#3:

An operational definition of HRm ax is needed to provide context for the current results.

Response to Comment#3:

We agree with this comment. In relation to this comment, we have changed the following points,

1) line 196-198: Replaced the following sentence

“The equations of Tsk, mean radiant temperature (Tr), dry or sensible heat loss (DHL), evaporative heat loss (EHL), total heat loss (THL), absolute humidity and total sweat loss are included in supporting information (S1 Methods-Calculations).”

with

“The equations of Tsk, mean radiant temperature (Tr), dry or sensible heat loss (DHL), evaporative heat loss (EHL), total heat loss (THL), absolute humidity, total sweat loss and maximal HR (HRmax) are included in supporting information (S1 Methods-Calculations).”.

2) S1 Methods-Calculations, the bottom of the text: Add the following sentence

“HRmax was calculated by subtracting the age from 220.”

We are afraid that our statistical adviser (Dr. Jos Feys, University of Leuven) has pointed out that the Tukey multiple comparison tests rather than the Kruskal-Wallis test with the Wilcoxon rank sum test are a practical and powerful approach to multiple testing in this TS data. The results of statistical analysis in the TS data were not different the present results when using the Tukey multiple comparison tests. Therefore, we would like to replace the following sentence, line 205-206,

“Pair-wise differences between trials were evaluated using the Kruskal-Wallis test with the Wilcoxon rank sum test.”

with

“Pair-wise differences between trials were evaluated using the Tukey multiple comparison tests.”

We are most grateful for your comments on our manuscript. We trust that the second revised version of our manuscript is suitable for publication.

Submitted filename: Response to Reviewer#2 R2.docx

Click here for additional data file.

12 Nov 2020

Greater thermoregulatory strain in the morning than late afternoon during judo training in the heat of summer

PONE-D-20-11199R2

Dear Dr. Otani,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Randy Wayne Bryner, Ed.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #2: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #2: No

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #2: Line 199 - consider using "age-predicted maximal HR"

The revision to "a regular judo training" from "regular judo training" is unnecessary.

**********

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Reviewer #2: No

16 Nov 2020

PONE-D-20-11199R2

Greater thermoregulatory strain in the morning than late afternoon during judo training in the heat of summer

Dear Dr. Otani:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

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PLOS ONE