Cardiovascular responses to millet pounding activity among women in a rural community in Northeastern Nigeria.

BACKGROUND: Pounding food items in a wooden mortal is a common home chore in many communities in African and Asian countries. However, no empirical data exist on energy expenditure during this activity, and whether the activity can be considered a light, moderate, or vigorous intensity physical activity is unknown.
PURPOSE: This study was aimed at gaining insights into energy expenditure during millet pounding through cardiovascular responses to millet pounding activity, and to explore possible differences in response between women who pound millet as their occupation (habitual millet pounders) and those who pound millet only for their own home cooking but not as a job (nonhabitual pounders).
METHODS: A total of forty apparently healthy women performed millet pounding activity in standing position for 15 min durations, and their cardiovascular parameters including heart rate (HR), systolic blood pressure (SBP) and diastolic blood pressures (DBPs), and rated perceived exertion (RPE) at rest, and immediately after pounding activity were assessed.
RESULTS: Significant increases in the subjects' cardiovascular parameters in the range of 7-12, 1-5, and 19-21 point values above the resting levels for SBP, DBP, and HR, respectively, were observed. Significantly higher SBP was also observed for the habitual pounders than the values for the nonhabitual pounders, whereas RPE was significantly higher for the nonhabitual pounders than for the habitual pounders in response to pounding.
CONCLUSION: This study suggests that millet pounding substantially stresses the cardiovascular system sufficiently to place the activity within the moderate intensity category. Further studies on energy cost of this house chore, using instrumentation that is capable of direct measure of oxygen consumption, is warranted. Résumé Contexte: Le fait de battre des aliments dans un mortier en bois est une corvée à domicile fréquente dans de nombreuses communautés des pays d'Afrique et d'Asie. cependant, Il n'existe pas de données empiriques sur la dépense énergétique au cours de cette activité et si l'activité peut être considérée comme une activité légère, modérée ou vigoureuse Intensité est inconnue. Objectif: La présente étude visait à mieux comprendre les dépenses énergétiques au cours de la Les réponses cardiovasculaires à l'activité battue du mil, et d'explorer les différences possibles dans la réponse entre les femmes qui pound millet comme leur (Millet pounders habituels) et ceux qui pound millet seulement pour leur propre cuisine à la maison, mais pas comme un emploi (pounders nonhabituel). Méthodes: Un total de quarante femmes apparemment saines ont effectué une activité de pilage du mil en position debout pendant 15 min de durée, et leurs Les paramètres cardiovasculaires, y compris la fréquence cardiaque (FC), la pression artérielle systolique (PAS) et les pressions artérielles diastoliques (PAD) (RPE) au repos, et immédiatement après l'activité de pilonnage ont été évalués. Résultats: Augmentation significative des taux de On a observé des paramètres situés dans la plage des valeurs de 7-12, 1-5 et 19-21 points au-dessus des niveaux de repos pour la PAS, la PAD et la HR respectivement. On a également observé une PAS significativement plus élevée pour les pounders habituels que pour les pounders non habituels, alors que la PPE était Significativement plus élevé pour les pounders non habituels que pour les pounders habituels en réponse à pounding.
CONCLUSION: Cette étude suggère Que le broyage du millet souligne sensiblement suffisamment le système cardiovasculaire pour placer l'activité dans la catégorie d'intensité modérée. D'autres études sur le coût de l'énergie de cette corvée maison, en utilisant une instrumentation qui est capable de mesure directe de la consommation d'oxygène, est justifiée.

Introduction

Heart rate (HR) and blood pressure (BP) are cardiovascular parameters regulated internally through the autonomic nervous system. Physiologically, BP tends to increase with age,[1] and disease and gender factors such as in the use of oral contraceptives, pregnancy, and hormonal changes during menopause, can all affect the BP of women.[2] External factors that affect cardiovascular responses may also include emotional stress, exercise and physical activity, smoking and food ingestion and eating. Exposure to danger, exercise and sexual intercourse all cause elevated HR, while during sleep and in aerobic fitness at rest, HR tends to be lower through the autonomic nervous system pathway.[34]

Pearl millet is one of the staple food sources for millions of people in the semi-arid zones of West Africa.[5] Traditionally, processing of millet for food in Northern Nigeria involves the removal of some of the outer layers of the kernel by pounding the grain in a wooden mortar with wooden pestle.[6] The decorticated grain is then steeped overnight in water containing tamarind bean extract or sour milk to bleach the pigments. The grain is subsequently sun dried and pounded in the wooden mortar and pestle to reduce the particle size to powdery form. The bleached flour can be cooked into porridge called tuwo.[7] Pearl millet can also be prepared and made into solid paste balls called fura, thin porridge called coco, pan cake as in massa or steamed granulated products such as couscous.[8]

The act of pounding millet in a mortar using a pestle is a complex coordinated process involving the action of many upper limb muscle groups. It involves moving the pestle through two phases of arm movement. The first phase involves an upward stroke, in which the pestle is lifted up against gravity to a height of about above the mortar brim. In the downward stroke, the pestle undergoes acceleration to pound the millet grains in the mortar. Pounding can be done using one limb, but women alternately transfer the pestle from one hand to another, or hold it with both hands as they begin to get tired during the pounding process. In general just as in many household chores, it is an activity that is mostly performed by women and adolescent girls.

Pounding involves vasalva, especially during the upward phases of the pounding motion. Millet pounding is done in standing position but may also be done in sitting. As in any upper extremity exercise, blood is re-directed to the arms, whereas the volume that flow through the lower limbs is decreased.[9] Therefore, compared to the resting state, an increase in BP and HR will be expected during this activity. Furthermore, compared to lower extremity exercises, upper extremity exercises can cause greater increases in BP because the former tend to increase the peripheral resistance to a greater degree than what may be expected in activities and exercises that involves the lower extremity muscles.[10]

Physical activity is considered to be light if the metabolic cost is <3 metabolic equivalents (METs), moderate if the cost is 3–6 METs and vigorous if the metabolic cost is >6 METs.[11] Generally, activities of daily living (ADL) tasks that involves isometric exercises produces a characteristic pressor effect or heightened BP more than dynamic activities.[12] ADLs that involves dynamic activity such as walking also leads to increase in HR and systolic BP (SBP), just as isometric exercises. Usually however, there could be no change or only a slight decrease in diastolic BP (DBP), in response to dynamic exercises.[1314]

There is consensus that the HR and rated perceived exertion (RPE) in response to exercises and physical activity can be used to estimate both energy expenditure and physical activity intensity.[1516] Consensus also exist that a MET estimation based on HR increase above resting values is adequate in estimating energy expenditure during exercises and physical activity, because it is based on an individual parameter of HR at rest, which can be related to an individual's aerobic capacity.[1718] A regression equation to estimate the MET following a walk/run test using net HR increment above the resting values, has been developed.[16] A net HR threshold values for light (<3 METs), moderate (3–6 METs) and vigorous physical activity (>6 METs) has been set as 16, 35, and 70, respectively.[16]

RPE scale is another method of estimating exercise intensity levels. It has been determined that moderate intensity physical activity burns 3.5–7 cal/min.[19] Physical activities that burn <3 cal/min or >7 cal/min are light and vigorous activities, respectively. Other ADL that involves burning calories at 3.5–7 cal/min are sweeping, heavy cleaning, and general carpentry.[11] These activities therefore can be expected to extol similar RPE values on the subjects performing the chores.

One previous study investigated the effect of high levels of habitual physical activity such as millet pounding and carrying head supported loads among West African adolescent girls and the relationship of these activities to maturation, growth, and nutritional status.[20] At present, no study on cardiovascular response to millet pounding was found and whether the activity can be considered to be vigorous- or moderate-intensity physical activity is unclear. This study was therefore aimed to determine the cardiovascular parameters during millet pounding and thereby gaining insights into the energy expenditure during this activity. It was also aimed to explore possible differences in the response between women who pound millet pounding as an occupation (habitual millet pounders [HMPs]) and those who pound for their own home cooking but not as a job (nonhabitual pounders [NHMPs]).

Methods

Participants

This pre- and post-test quasi-experimental study utilized a sample of 40 women who were 18–50 years old residing in a rural community in Northeastern Nigeria. These women comprising twenty women who pound millet for a living (HMP) and twenty who pounds millet only as house chores for home cooking and consumption NHMPs, participated in this study.

Study procedure

Following approval by the Research and Ethical Committee of the University of Maiduguri Teaching Hospital, visits were made to the homes of potential recruits in Jajimaji ward of Karasuwa Local Government Area, Yobe State, Northeastern Nigeria. Participants were first visited in their homes to introduce them to the study and to seek their consent to enroll. Consented participants were interviewed for medical history of high BP and were advised not to engage in activities that can lead to physical exertion 2 h before the next scheduled visit. On the second visits made to the homes of the consented participants between 7:00 and 11:00 a.m. Mondays through Fridays of the weeks in the month of March 2014, participants height and weight were measured after which they were made to sit on a stool, leaning their backs against the wall in the courtyard of their homes for 5 min. Their resting cardiovascular parameters (HR, and BPs) were then taken.

While still seated, the participants were provided with instructions on the pounding activity and questions were entertained. Millet grains were then soaked for 2–3 min and were poured into the mortar placed on a smooth and level surface close to the participant. Participants were asked to begin pounding with the wooden mortar and pestle in standing position for duration of 15 min. After the completion of the pounding activity, the participants were immediately seated and their cardiovascular parameters were then monitored serially, first within 1 min into recovery, and then subsequently after every 3 min thereafter, for 9 min. RPE of the subjects were also measured 10 min into recovery with the instruction to indicate their response on the RPE scale according to how they felt immediately after pounding.

Data analysis

Descriptive statistics of mean, frequency, and standard deviation were used to describe the participants’ sociodemographic characteristics. Paired t-test was used to determine the difference between baseline cardiovascular parameters and the values after millet pounding. Analysis of variance and where applicable, analysis of co-variance was used to determine the differences in the recovery HR and BP between HMPs and NHMPs. The alpha level was set at 0.05.

Results

Of the total of 40 women who participated in the study, 30 (75.0%) were married, 2 (5.0%) were single and 4 were divorced (10.0%), and another 4 (10.0%) were widowed. Ten participants (25.0%) five in each group, had a job in addition to being housewives. The mean age and body mass index of the participants were 35.2 ± 9.7 (95% confidence interval = 32.13–38.27 years) and 22.9 ± 3.6 (95% confidence interval = 21.76–24.04) kg/m2, respectively. The mean age and body mass index of the HMPs were 37.7 ± 78 years and 23.4 ± 3.4 kg/m2, respectively, whereas the mean age and body mass index of nonhabitual pounders were 32.8 ± 11.0 years and 22.5 ± 3.8 kg/m2, respectively [Table 1]. No significant differences by sociodemographic or physical characteristics were observed between the groups.

Table 1

Physical Characteristics of the Participants

Variables	Groups		Combined
	H	NH
Ageb	37.7±78	32.8±11.0	35.2±9.7
Heightb	1.59±0.66	1.61±0.05	1.6±0.06
Weightb	58.7±8.0	58.7±9.0	58.7±8.4
BMIb	23.4±3.4	22.5±3.6	22.9±3.6

BMI=Body Mass Index, H=Denotes habitual millet pounder group, NH=Denotes non-habitual millet pounder group, Superscript b means no significant difference between habitual (H) and non habitual (NH) millet pounders

When comparison of the cardiovascular parameters between the groups at the different time frames were made, it was observed that the baseline HR of the HMP group was significantly lower (P < 0.05) than that of the NHMP group (P < 0.05), whereas the baseline values for the SBP, DBP, and the derived indices were not different between the groups [Table 2]. HR, SBP, DBP, mean arterial BP (MAP), and 9 min recovery DBPs, MAPs, and RPEs were significantly higher after 15 min of pounding activity than the baseline values. No significant difference (P < 0.001) was found between the baseline RPE for the subjects by groups. RPE following pounding was however significantly lower (P < 0.05) for the HMP group than their NHMP counterparts.

Table 2

Comparison of cardiovascular parameters at rest, immediately after pounding and recoveries

Variable	b vs x	b vs r	b vs s	b vs t
Heart Rate
H	76.7±9.6x vs 97.4±12.7	76.7±9.6 vs 89.1±12.1a	76.7±9.6 vs 86.6±11.8a	76.7±9.6 vs 86.0±10.9a
N	83.9±8.2x vs 102.8±13.7	83.9±8.2 vs 92.5±16.6a	83.9±8.2 vs 90.4±11.6a	83.9±8.2 vs 87.2±11.0
C	80.3±9.5 vs 100.1±13.3	80.3±9.5 vs 90.8±11.8	80.3±9.5 vs 88.5±11.7	80.3±9.5 vs 86.6±10.8
Systolic Blood Pressure
H	115.3±9.6 vs 127.2±13.7xa	115.3±9.6 vs 114.6±9.9	115.3±9.6 vs 109.2±10.2a	115.3±9.6 vs 75.3±10.8
N	112.3±9.9 vs 118.2±10.6xa	112.3±9.9 vs 110.3±10.6b	112.3±9.9 vs 105.5±9.9a	112.3±9.9 vs 66.5±9.9a
C	113.8±9.8 vs 122.6±12.9	113.8±9.8 vs 112.4±10.3	113.8±9.8 vs 107.2±10.2	113.8±9.8 vs 101.6±9.8
Diastolic blood pressure
H	79.9±9.7 vs 84.4±12.3xb	9.9±9.7 vs 76.8±11.3xb	79.9±9.7 vs 75.2±11.8b	79.9±9.7 vs 84.4±12.3xb
N	77.2±9.7 vs 76.5±8.8x	77.2±9.7 vs 69.3±9.0xa	77.2±9.7 vs 66.5±8.3a	77.2±9.7 vs 76.5±8.8xa
C	78.6±9.4 vs 80.4±11.3	78.6±9.4 vs 73.0±10.8	78.6±9.4 vs 70.8±11.0	78.6±9.4 vs 70.9±10.8
Mean arterial pressure
H	92.5±11.3 vs 98.6±11.6xa	92.5±11.3 vs 89.3±10.3x	92.5±11.3 vs 85.8±9.9xa	92.5±11.3 vs 87.0±8.9xa
N	88.7±9.0 vs 90.0±8.2xb	88.7±9.0 vs 82.8±8.6xa	88.7±9.0 vs 79.4±8.2xa	88.7±9.0 vs 79.1±9.0xa
C	90.8±15.2 vs 94.3±10.8	90.8±15.2 vs 86.0±9.9	90.8±15.2 vs 85.6±9.6	90.8±15.2 vs 83.1±9.7
Pulse pressure
H	35.4±6.2 vs 42.8±11.3	35.4±6.2 vs 37.8±7.2	35.4±6.2 vs 35.0±6.9	35.4±6.2 vs 35.2±10.0
N	35.1±7.5 vs 41.6±9.5a	35.1±7.5 vs 49.5±39.1	35.1±7.5 vs 38.7±7.0	35.1±7.5 vs 38.2±7.0b
C	35.2±6.8 vs 42.2±10.3	35.2±6.8 vs 43.6±28.4	35.2±6.8 vs 36.8±7.1	35.2±6.8 vs 36.7±8.6
Rate Pressure Product
H	87.7±10.6 vs 123.6±19.9a	87.7±10.5 vs 101.7±14.6a	87.7±10.5 vs 94.4±15.4	87.7±10.5 vs 95.1±15.4
N	94.4±14. vs 12.2±22.1a	94.4±14.3 vs 102.6±19.0	94.4±14.3 vs 95.0±16.3	94.4±14.3 vs 86.7±22.7
C	91.0±12.9 vs 122.7±20.8	91.0±12.9 vs 102.1±16.7	91.0±12.9 vs 94.7±15.6	91.0±12.9 vs 90.9±19.6

H=Habitual pounders, N=Non habitual pounders, C=Combined groups, b=Baseline, x=Exercise, r=First recovery, s=Second recovery, t=Third recovery, Rate Pressure Product values are in ’00. Exercise values are values immediately on cessation of pounding; r values are values 3 minutes on cessation of pounding; s values are values 6 minutes after cessation of pounding; t values are values 9 minutes after cessation of pounding; RPP value are in ’00 Superscript a means P<0.01 while b means P>0.01 but less than 0.05. Superscript x means there was a significant difference between habitual (H) and non habitual (NH) pounders

No significant difference (P > 0.05) was observed in the HR and SBP between the groups following pounding. However, SBP, DBP, and MAP were significantly higher (P < 0.05) for the HMPs than their nonhabitual counterparts, immediately after pounding activity [Table 2]. No significant difference (P > 0.05) was observed between the HR and SBP of HMPs and their nonhabitual counterpart 3 min after the cessation of pounding (first recovery). However, the DBP and MAP were significantly higher (P < 0.05) in the habitual group than the nonhabitual group of participants 3 min on cessation of pounding. No significant difference (P > 0.05) was found in the pulse product (PP) and rate pressure product between the groups 3 min after pounding.

Nine min after the pounding activity, also, no significant difference (P > 0.05) was observed in the HRs between the groups. No significant difference (P > 0.05) was found in the SBP between the groups 9 min following pounding. Significantly higher DBP (P < 0.05) was however observed for the habitual pounder group compared to the nonhabitual group of participants 9 min following the pounding activity. Furthermore, a significantly higher (P < 0.05) MAP was observed for the HMPs group than their nonhabitual pounders counterparts, 9 min following pounding. No significant difference (P > 0.05) was observed between the PP of habitual and NMPs 9 min after the pounding activity.

We computed the scale of change for the subjects HR, BP, and RPE in response to pounding activity to gain some insights into the scale of the energy expenditure of subjects during pounding activity.[16] The mean difference in SBP, DBP, and HR between the baseline and their corresponding postpounding values postpounding activity for the subjects are 11.9 ± 7.3, 4.5 ± 8.6, 20.7 ± 9.2 and 5.8 ± 3.9,−0.8 ± 9.3, 19.0 ± 8.2 for the HMP and NHP groups, respectively. The results show significantly higher change (P < 0.05) in SBP and DBP in the HMP group than that of their NHP counterparts. For all subjects combined, the mean RPE of 14.8 ± 3.0 following pounding was significantly higher than the baseline value of 6 ± 0. Significantly higher RPE was observed for the NHP group compared to that of the HMP group (17.5 ± 1.5 vs. 12.2 ± 1.2, respectively) in response to pounding activity.

Discussion

Although the estimated energy cost of some common ADL has been documented in the literature, the energy cost of some specific ADL common in the developing African countries such as millet pounding is undocumented. One objective of this study was to gain insights into the energy cost of millet pounding through cardiovascular parameters in response to the activity. The change in HR observed in this study for both the habitual and the nonhabitual pounders being 20.7 ± 9.2 and 19.0 ± 8.2, respectively, the energy expenditure during pounding activity can be estimated to be 4 METs or better. Furthermore, because the mean RPE of the participants in response to millet pounding is 14.8 ± 3.0, a value which falls within the RPE range of 12–16 as proposed[15] millet pounding activity may therefore be classified as a moderately intense physical activity.

Based on the scale of the HR change and RPE following millet pounding, this activity can be argued to be within a 4–6 METs level. This finding suggests pounding activity as a moderately intense or hard physical activity comparable to activities such as brisk walking, carrying light load, bicycling, and sweeping of the compound. It can therefore be argued that pounding activities such as the one performed in the present study, if done for at least 10 min continuously at any one time, can be counted toward the weekly minimum of 150 min of moderately intense physical activity for health enhancing benefits toward the mitigation of noncommunicable diseases.[2122]

Caution must be entertained in prescribing pounding activity to patients even though millet pounding is an activity that can be counted towards the physical activity minutes requirement for health enhancing purpose because its intensity level places it among the group of exercises in the moderate intensity category. Prescribing it for cardiac patients, especially postthoracotomy may not be recommended because just as any pounding activity, it involves a repetitive motion that may not be suitable to patient who recently underwent thoracic surgery. Pounding activity also involves vasalva, and unless patient is adequately trained in the appropriate breathing technique, undue heightening of BP may result. Caution may therefore also be warranted in prescribing this activity for hypertensive patients.

Higher RPE among nonhabitual pounders compared to their habitual pounders suggests the former incur higher metabolic cost of millet pounding activity than the later. Women who pound millet for a living may also pound for their cooking at their own homes and can therefore be deemed to be better conditioned for this activity than their counterparts who do not pound for a living. The apparently lower energy cost incurred by the habitual pounder group compared to their nonhabitual group may therefore be attributed to the training effect conferred on the former.[23] Following exercise and physical activity, there is some training effect that may be characterized by potentially more glycogen storage in an adapted muscle of the HMP group compared to the storage in the NHP group.[23] A trained muscle group may be able to sustain contraction before fatigue sets in and a trained muscle contains much greater capacity to store muscle glycogen than an untrained muscle group.[23]

Finding in this study that higher SBP response observed for the HMPs than their nonhabitual counterparts is comparable to what was reported in other studies[2425] which show that the SBP of a person that exercises regularly may likely rise higher during exercises and physical activity than it could rise for sedentary subjects. Considering that the weight of the pestle is a substantial loading on the body findings in this study can be compared to that of a previous report which shows that resistance exercises can lead to higher increase in both SBPs and DBPs in well trained individuals than in sedentary individuals.[26]

Our finding that revealed a significantly higher MAP for the HMP group compared to their NHP counterparts is in agreement with the finding in another study in which the responses of trained and untrained groups were compared.[24] The authors attributed their findings to higher increases in cardiac output expected in the trained subjects versus the untrained ones. The absence of difference in pulse pressure (a correlate of stroke volume) between the groups is in agreement with the finding in another study.[27] The study explained the comparability of pulse pressure by the anticipated increase in the diameter of the blood vessels in response to pounding activity which is expected, regardless of the training status. It is however at variance with a study which showed that athletes who trained with weights showed higher pulse pressure than their sedentary counterparts.[28]

Study limitation

In this study, the subjects’ cardiovascular parameters in response to millet pounding were not monitored while performing the activity. Instead, they were monitored within 30 s following cessation of pounding. With the appropriate instrumentations, the steady state responses of the subjects can be monitored during pounding without waiting until the cessation of the activity. Nevertheless, it can be safely presumed that values obtained within 30 s after the cessation of activities can be argued to be a good estimate of the steady state values that could have been obtained while still performing the activity. The 30 s postpounding measurements can therefore be safely substituted for a steady state pounding response.

Authors recognized that oxygen consumption measures are the gold standard for accessing energy cost of activities. Therefore, HR and RPE as employed in this study are only indirect measures of oxygen consumption and energy cost of millet pounding activity. HR and RPE are indicators of physical activity intensity and are not substitutes for oxygen consumption, but they were monitored and utilized as indirect measures of energy cost, in the absence of instrumentations capable of oxygen analysis. Future studies using the appropriate instrumentations that could monitor oxygen consumption and perform the necessary gas analysis to provide better information on the energy cost of pounding activity is warranted.

Conclusion

This study shows that millet pounding substantially stresses the cardiovascular system enough to be categorized as a moderately intense physical activity, comparable to physical activities such as brisk walking, carrying light load, and bicycling. It also suggests that there is cardiovascular adaptation characterized by higher increase in systolic and MAP in HMPs compared to their nonhabitual pounder counterparts. This exploratory study suggests pounding activity is a moderately intense physical activity that is includible in exercise and physical activity prescription within the 4–6 METs category. Further study to accurately assess the MET of millet pounding, using equipment that are capable of analyzing oxygen intake such as a metabolic cart, is warranted.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.