Postural stability of 5-year-old girls and boys with different body heights.

BACKGROUND: Postural stability is one of the determinants of proper body posture and a condition for developing motor abilities in every human being. The measurement of the centre of pressure (COP) location and displacement is the most common technique of postural stability assessment.
OBJECTIVE: The aim of this study was to assess differences in postural stability depending on sex of 5-year-old children with different body heights.
METHODS: A study included 435 healthy children (200 girls and 235 boys) born in 2010 whose parents gave a written consent to their participation in the project. Postural stability was assessed with the use of the dynamographic platform (Zebris FDM 1.8). The assessment of postural stability was based on COP shift parameters (sway path length of COP and average velocity of COP) and COP surface area parameters (area of the ellipse, length of ellipse in the anterior-posterior direction and length of the ellipse in the medial-lateral direction). Body height was measured with Holtein anthropometer and the obtained values were compared with percentile ranks determined by the WHO.
RESULTS: The analysis of the parameters describing postural stability in the examined children revealed dimorphism. For the COP shift parameters and COP surface area parameters, the level of statistical significance was recorded for girls and boys. Girls achieved lower results of these parameters than boys regardless of their body height. In the groups of normal- and tall-statured children, differences between the genders were statistically significant.
CONCLUSIONS: The present study characterised sex differences in postural stability of 5-year-old children. Sex-related differences were found during a natural stance for all COP parameters. Girls maintained a two-legged standing position with lower sway velocity and a smaller range of sway than their male counterparts. Normal- and tall-statured girls demonstrated better postural stability significantly more often than boys.

Introduction

Being able to maintain standing balance is the basis of a child’s motor development. The fifth and the sixth year of life is a period of positive changes in physical fitness and motor coordination. During childhood, children begin to learn and acquire many fundamental motor skills. Adequate acquisition and command of fundamental motor skills at the end of preschool age (around the age of six) have been considered as crucial elements in the development of specialised and more complex motor skills [1, 2]. Proper postural stability is the basic condition when it comes to improving motor skills specific to children [3].

Vertical positioning of the body axis in relation to the support area is a characteristic feature of body posture. To achieve and maintain an upright standing position, efficient postural control is required. Postural control is a complex process that depends on the integration between the sensory and musculoskeletal systems [3, 4]. Upright posture control includes minimising body sway so that the vertical projection of the centre of mass (COM) is maintained within limits of the base of support. Body sway is treated as an indicator of the balance system efficiency. It can be assessed by measuring the deviations in the location of the vertical ground reaction force vector (the centre of pressure, COP) on the supporting surface. In the sagittal plane (AP–anterior-posterior), these forces are generated by muscles responsible for ankle joint movements, while in the frontal plane (ML–medial-lateral), forces are produced by hip abductors and adductors [5, 6, 7]. Larger COP oscillations are considered to be the signs of postural instability.

Body posture and stability change in the course of ontogenetic development. Movement patterns, muscle tone and the sensory system also develop in the process of ontogenesis. Although somatic changes in a child may affect the level of body posture control, it is the development of the sensory nervous system and vestibular system that affect body posture stability to a larger extent [8, 9, 10]. The control of body balance in children becomes more and more efficient as the latent period of muscle contraction shortens and the velocity of neuromuscular transmission increases [11]. The quality of the transmission of sensory and motor stimuli is also affected by the myelination of nerve fibres. Muscle strength increases together with the development of muscle tissue, innervation, proprioception and an ability to engage a maximal amount of neuromuscular motor units in a movement. In a child between 4 and 7 years of age, this increase constitutes 75% of the baseline strength from the age of 4. Moreover, around the age of 5, the process of the development of extensor mass accelerates and extensor tonus balances the tension of flexors. This process facilitates the maintenance of an upright body position. In a child aged 5–7, the mass of extensors is 2–3 times bigger than the mass of flexors in particular lower limb joints [12]. By 6 years of age, though, children have achieved adult levels in some specific aspects of postural control [9, 13, 14]. The biggest developmental changes regarding balance control occur in children aged 6–8 [15, 16, 17].

Research on postural stability performed with the use of various platforms is carried out more and more often and concerns different age groups. However, these studies are usually of comparative character or reflect postural stability of children and youth with certain developmental dysfunctions. Researchers often carry out studies on children of both genders together or divide children into two age categories by combining 3- and 4-year-olds in one group and 5- and 6-year-olds in another. In turn, publications on postural stability of small healthy children born in the same year are less common.

In the 5th year of life, gender has proved to be an important factor in acquiring and mastering fundamental motor skills. Sex differences exist during childhood and may be credited by various factors, i.e. biological, physical, psychological. Maturational differences between girls and boys do not only exist regarding physical, hormonal, and sexual development, but also in terms of central nervous structures. It was indicated that brain structure and development differ between sexes during infancy [18, 19, 20]. Girls are better at skills which require balance and rhythm as well as precision, e.g. tiptoeing, walking on a balance beam or walking foot by foot, one-leg balance on the preferred leg, which are stimulated by the vestibular system. In turn, boys achieve better results in activities which require more speed and strength [21, 22, 23]. Webster et al [24] also showed that boys engaged more in total physical activity, moderate-vigorous physical activity, and less in sedentary behavior.

Can we, therefore, expect postural stability of girls to be better than in boys? The aim of this study was to assess differences in postural stability depending on sex of 5-year-old children with different body heights. It is hypothesised that girls have better postural stability than boys, reflected by a decrease in the amount of sway among girls.

Materials and methods

Participants

The study was carried out on 435 healthy 5-year-olds (62.1±3.47 months) from Poland including girls (n = 200) and boys (n = 235), which constituted 76% of the total number of 5-year-olds attending kindergartens in Biala Podlaska in the school year 2015/2016. The inclusion criteria were as follows: a) being born in 2010, b) attending a kindergarten in the school year 2015/2016, c) participants of both sexes, d) good general health. Children were excluded from the study if they: a) had any neurological and musculoskeletal disorders confirmed by their parents/guardians, b) had bad general health. No child had a dysfunction that could impair their ability to maintain balance.

Written informed consent was obtained from the parents/guardians of all the children enrolled in the study. The research was conducted within the statutory research project DS. 246 titled “Psycho-physical development of 5-year-olds from Biała Podlaska”, which was accepted by the Research Commission of the Faculty of Physical Education and Sport in Biała Podlaska and the Senate Scientific Research Ethics Commission of Józef Piłsudski University of Physical Education in Warsaw (SKE 01-01/2014). The examinations on postural stability were performed between November 2015 and January 2016 in the Body Posture Laboratory at the Regional Centre for Research and Development of the University College in Biała Podlaska. All the examinations were made in the morning hours in the laboratory rooms in which safety, intimacy and basic hygienic requirements were ensured.

Test procedure and protocol

Stage I–preparation

At the preparation stage (April–August 2015), talks with kindergarten directors and teachers were initiated and information meetings with parents were held in order to obtain their consent to include their children in the project. The purpose and procedure of this study were explained in detail to parents and kindergarten teachers.

Stage II–initial medical check-ups

Prior to the examinations, the children underwent initial medical check-ups which qualified them to participate in the study. General health state was assessed on the basis of heart and lungs auscultation in a standing position and the examination of blood pressure using the auscultation method in a sitting position [25].

Stance analysis

Postural stability was assessed with the use of the dynamographic platform Zebris FDM 1.8 (Force Distribution Measurement, 208x56 cm, 120 Hz, System Stance Analysis, Medical GmbH, Germany), which measures the COP signal. The platform was connected to the WinFDM software for analysing body sway. The measuring device was calibrated prior to the examination of every child. During the measurement, the COP signal was registered. After the registration, the system automatically performed basic analyses of the registered signals.

Children were examined individually while standing on a platform in a place indicated by the researcher. The task involved maintaining a two-legged stance with eyes open for 30 seconds. Children were standing barefoot with their legs straightened in the knee joints and their feet parallel to each other, their upper limbs along their torsos and their heads in the Frankfurt plane.

In case of noticeable movements of the head, upper limbs or lower limbs, a child repeated the test a few minutes later. The duration of a single test made it possible to detect COP oscillations reflecting real conditions and at the same time not evoking a negative attitude of children [26].

The assessment of postural stability was based on five sway parameters: COP shift parameters (sway path length of COP and average velocity of COP) and COP surface area parameters (area of the ellipse, length of the ellipse in the anterior-posterior direction and length of the ellipse in the medial-lateral direction):

sway path length of COP (SP) [mm]–defines the total length of path marked by the COP; the sum of distances between the locations of the COP constitutes the path length;

average velocity of COP (V) [mm/s]–defines mean velocity at which the COP moves; this parameter indicates the speed of changes in the COP location, which reflects the speed of postural reactions while standing;

area of the ellipse (AoE) [mm2]–defines the size of the area marked by the COP; ellipse area includes 95% of the COP measurement points; this parameter makes it possible to assess the size of the area of the COP movement on the support surface;

length of the ellipse in the anterior-posterior direction (LoEAP) [mm];

length of the ellipse in the medial-lateral direction (LoEML) [mm].

Each sway parameter was evaluated as follows: the higher the parameter score, the greater the sway and the worse the postural stability.

Body height measurement

The characteristics of postural stability of the examined children required assessing sex-related differences in the groups of children at a similar level of physical development taking into account body height.

The measurement of body height is a standard manner of monitoring a child's growth and development [27]. Body height was measured with Holtein anthropometer with the accuracy of 0.1 cm. The examined children born in 2010 manifested various values of body height increase. Mean values of this parameter in girls were 1.14±4.89 and in boys– 1.15±5.38, and differences between them were statistically significant (U = 26664, p = 0.02).

In order to minimise differences in body height, body height values of study participants were compared to the body height values created by WHO for children in particular months of life. WHO 2006 standard is the outcome of a multinational study. Growth charts are widely used as a clinical tool to monitor growth in individual children. Height status was classified according to age and gender into low stature (-1) (<25th percentile), normal stature (0) (≥25th percentile to ≤75th percentile) and tall stature (1) (>75th percentile) based on the percentile ranks determined by the WHO [28]. In this way, children at a similar level of physical development were selected.

Statistical analysis

The collected material was organised and analysed with the use of Statistica 13 calculation software by Statsoft (PL). The parameters were described using basic measurements of descriptive statistics, i.e. mean, standard deviation (SD), median (Me). The compliance of the results with normal distribution was checked with the Shapiro-Wilk test. Data normality was rejected, so the Mann-Whitney U test was used to examine sex differences regarding body height values and postural stability parameters. Statistical significance was set at p<0.05.

Results

The results of measures describing COP shifts recorded with regard to sex are presented in S1 Fig. For the sway path length (SP) and average velocity (V) of the COP, the level of statistical significance was recorded for girls and boys. The analysis of the COP shift parameters describing the process of maintaining static balance in the examined children revealed that girls achieved significantly lower values of these parameters than boys (sex effect for SP: U = 17312.5, p<0.001; gender effect for V: U = 17229.5, p<0.001). Moreover, sex differences in COP shift parameters taking into account body height categories were noted. Girls achieved lower results of these parameters than boys regardless of their body height. In the groups of normal- and tall-statured children, differences between the sexes were statistically significant (normal-statured, sex effect for SP: U = 6655.5, p = 0.002, sex effect for V: U = 6608, p = 0.001; tall-statured, sex effect for SP: U = 2152, p<0.001, sex effect for V: U = 2145.5, p<0.001). The percentage of children taking into account body height categories determined by the WHO is shown in Table 1. Mean and median values of measures describing COP shifts recorded in girls and boys taking into account body height categories determined by the WHO are presented in Table 2.

Table 1

The percentage of children taking into account body height categories determined by the WHO.

		Body height categories determined by the WHOn (%)
		1	0	-1
Sex	Girls (n = 200)	69 (34.5)	127 (63.5)	4 (2.0)
	Boys (n = 235)	94 (40.0)	135 (57.4)	6 (2.6)
All (n = 435)		163 (37.5)	262 (60.2)	10 (2.3)

Note: n—number of children; %—percentage; (1) tall-statured children; (0) normal-statured children; (-1) low-statured children.

Table 2

Mean (SD) and median values of COP parameters taking into account sex and body height categories determined by the WHO, and significance levels from the Mann-Whitney U test.

Body height categories determined by the WHO	COP parameters	Girls		Boys		p value
		Mean±SD	Me	Mean±SD	Me
1(n = 163)	SP [mm]	517.7±171.33	503.0	621.2±186.60	602.4	<0.001
	V [mm/s]	18.0±5.90	17.6	21.6±6.50	20.8	<0.001
	AoE [mm2]	792.4±463.35	678.6	1165.0±636.23	1046.0	<0.001
	LoEAP [mm]	32.5±11.73	30.6	35.5±12.04	35.0	0.049
	LoEML [mm]	30.6±14.77	28.2	40.7±16.31	38.2	<0.001
0(n = 262)	SP [mm]	570.6±177.45	549.7	644.3±197.69	630.1	0.002
	V [mm/s]	19.8±6.15	19.1	22.5±7.09	22.0	0.001
	AoE [mm2]	886.9±533.30	758.5	1029.7±555.79	947.9	0.021
	LoEAP [mm]	32.6±11.34	31.2	35.2±12.58	33.1	0.11
	LoEML [mm]	33.8±14.42	31.7	36.8±15.35	35.2	0.16
-1(n = 10)	SP [mm]	430.4±81.81	403.2	612.2±225.63	578.2	No test was performed due to the small size of the group
	V [mm/s]	15.0±2.87	14.0	21.3±7.86	20.2
	AoE [mm2]	652.6±275.18	651.5	679.7±345.72	687.6
	LoEAP [mm]	27.1±11.10	24.9	28.4±12.22	25.9
	LoEML [mm]	30.4±3.75	31.4	29.9±9.47	29.1

Note: n—number of children; SD–standard deviation; Me–median; SP–sway path length of COP; V–average velocity of COP; AoE–area of the ellipse; LoEAP–length of the ellipse in the anterior-posterior direction; LoEML–length of the ellipse in the medial-lateral direction; (1) tall-statured children; (0) normal-statured children; (-1) low-statured children. Statistical significance was set at p<0.05.

A statistically significant sex effect was observed for COP surface area parameters (S1 Fig). Girls achieved significantly lower values of these parameters than boys (sex effect for AoE: U = 18044.5, p<0.001; sex effect for LoEAP: U = 20418.5, p = 0.018; sex effect for LoEML: U = 18631, p<0.001). The analysis revealed sex differences for COP surface area parameters in the groups of low-, normal- and tall-statured children (Table 2). Girls achieved lower results of these parameters than boys regardless of their body height. For AoE in the groups of normal- and tall-statured children, Mann-Whitney U test showed a statistically significant sex effect (U = 7157.5, p = 0.021; U = 2091, p<0.001; respectively). A statistically significant effect of sex was observed for LoEAP and LoEML in the group of tall-statured children (U = 2657.5, p = 0.049; U = 1957, p<0.001; respectively). In the case of LoEAP and LoEML in the group of normal-statured children, sex effect was not significant (p = 0.11; p = 0.16, respectively).

Discussion

The aim of this study was to assess differences in postural stability depending on sex of 5-year-old children with different body heights. This aim was achieved through recording the amount of sways within 30 seconds in the same age group.

The present study revealed that sex-related differences were found during a natural stance for COP shift parameters (sway path length of COP and average velocity of COP) and COP surface area parameters (area of the ellipse, length of the ellipse in the anterior-posterior direction and length of the ellipse in the medial-lateral direction). Girls achieved lower values of all COP parameters than boys. It means that girls maintained a two-legged standing position with lower sway velocity, a smaller range of sway and a smaller area of the ellipse than their male counterparts.

The findings of the present study are in line with the studies which show that girls at different ages have lower values of COP parameters. Geldhof et al. [29] noted that girls aged 9–10 achieved lower values of sway velocity compared to boys, which indicates better postural control in girls. Lee and Lin [30] revealed that boys had significantly larger mean radius of COP distributions than girls in the eyes-open and eyes-closed conditions. With respect to sex differences, boys had significantly poorer single-leg stance postural stability than girls. Smith et al. [31] showed that girls aged 8–12 had better postural stability than boys in normal standing conditions (hard surface, eyes open and looking straight ahead). Differences between sexes are reflected in lower path velocity, smaller radial displacement and lower area velocity of COP in girls than in boys [31].

The results of this study show that girls had better postural stability than boys. In line with this, Steindl et al. [32] also noted that girls were able to maintain balance more accurately than boys in the age groups below 11–12 years, with the exception of the group of 5-6-year-olds. Females showed a greater rate of improvement in stability until 11–12 years of age [32]. Venetsanou and Kambas [22] reported that girls in preschool age outperformed boys in the following tests: standing on the preferred leg on the floor, standing on the preferred leg on a balance beam, standing on the preferred leg on a balance beam–eyes closed, walking forward heel-to-toe on a walking line, walking forward heel-to-toe on a balance beam. In turn, boys had significantly higher scores in walking forward on a balance beam. However, according to the authors, the effect of sex on BOTMP (Bruininks-Oseretsky Test of Motor Proficiency) balance items was weak, indicating that the observed superiority of the girls was not of great importance [22]. Paniccia et al. [33] also found sex-based differences in postural stability performance between girls and boys in athletes aged 9–12, whereby girls had better postural stability compared to boys in conditions in which visual information was presented.

Differences between sexes are equivocal in the literature. Other researchers report no significant sex differences in balance skills at the age of 5–6 [16, 32, 34, 35]. It may be assumed that differences in the obtained results may depend on the use of different methods, measuring platforms or tests, different numbers of study participants or different age groups.

In the 5th year of life, an accelerated increase in body length (changes in the somatic development) which makes the body slimmer is observed. Significant differences in physique (body dimensions) are visible, which creates different conditions for maintaining a stable body posture. In order to minimise differences in body height, body height values of study participants were classified into three categories determined by the WHO [28]. The present study showed that significant effects of sex on postural sway parameters were noted in the groups of normal- and tall-statured children.

The present study suggests that sex differences in postural stability in children with similar body height are not influenced by their physique. Sex differences in postural stability among children may explain maturational differences of central nervous structures [16, 36]. Girls seem more capable of integrating their sensory inputs under normal standing conditions, while boys treat each sensory input somewhat separately with less integration [37]. Moreover, Hirabayashi and Iwasaki [38] showed that girls aged 7–8 were significantly superior to boys of the same age in the use of the vestibular cues under the condition of no visual cues and inaccurate somatosensory input. In line with this, Smith et al. [31] and Peterson et al. [37] also suggested that girls had better postural control under normal standing conditions (with information obtained by the vestibular system). Females up to the age of 11–12 developed sensory systems earlier than males [32]. Girls are better at skills which require balance and rhythm, which are stimulated by the vestibular system. In turn, boys tend to spend more time engaged in moderate-to-vigorous physical activity and achieve better results in activities which require more speed and strength [21, 22, 23, 24]. Consequently, boys may be at an advantage over girls in terms of proactive balance as they can compensate worse balance with greater muscle strength [35]. It is possible that maturational slowness of the vestibular function seen in young boys is one of the factors responsible for the fact that boys are prone to be more active than girls [32, 38].

Limitations

A limitation of the present study is that the analysis of differences in postural stability was limited to two factors, i.e. sex and height, in one age group. However, these limitations did not affect the value of the presented results significantly. Further studies require consideration of other variables.

Study strengths

Studies investigating preschoolers' postural stability or balance skills do not provide a clear picture of children's postural stability at the age of 5. The data from this study provide evidence that postural stability differs between sexes already at this stage of development. Due to a large number of the study participants, the obtained results may have a normative value for children in this age group and be the basis for comparative analysis in different populations of children. Lastly, height status was classified according to age and sex into low, normal- and tall-statured, which enabled us to compare postural stability between girls and boys taking into account similar height.

Conclusion

The current study presents sex differences in postural stability of 5-year-old children. Sex-related differences were found during a natural stance for COP shifts and COP surface area parameters. Girls maintained a two-legged standing position with lower sway velocity, with a smaller range of sway and a smaller area of the ellipse than their male counterparts. Normal- and tall-statured girls demonstrated better postural stability significantly more often than boys.

Boxplot graphics—Values of COP parameters among children with regard to sex and significance levels from the Mann-Whitney U test.

(TIF)

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Dataset.

(XLS)

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17 Sep 2019

PONE-D-19-20547

Postural stability of 5-year-old children with different levels of body height

PLOS ONE

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https://www.brainanddevelopment.com/article/0387-7604(95)00009-Z/pdf

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Reviewer #1: Dear authors, I enjoyed reading your paper. The large sample of 5 year olds can provide a good insight into postural control at that age. Differences between genders are equivocal in the literature and therefore studies are needed. However, I do have some concerns about your paper. The paper is not clear from the linguistic standpoint. I think, overall it would be good to have the document proof-read. The introduction includes an excessive amount of information about the COP that experts do not need while other parts of your paper are lacking information. In terms of the methodology, I have reservations regarding the use of three ranges of COP velocity since those could be chosen randomly as well as parts of the statistical analysis. The discussion seems weak in terms of the amount of information coming from your study. In general, the paper lacks of justifications and citations. A major review is needed. You can find a more detailed review below.

Major issues

1. Lines 80-105. There is over one page regarding basic information about the COP and how to obtain it. Experts in the field do not need that information. You should reduce this part.

2. Lines 94-104. You are using very old references. The studies are relevant in our field but, there is more recent literature better explaining your points and correcting some of the affirmations from those authors. For example, I suggest these two articles:

a. Motor mechanisms of balance during quiet standing, by David A. Winter et al (same author that you cite but more recent).

b. Human Postural Control, by Yury Ivanenko and Victor S. Gurfinkel

3. Lines 137-139. You are using the term “levels” for postural stability and for body height. I would rather suggest using greater/worse/more/less/higher/lower instead of levels since there are no established levels of either.

4. Lines 146-147. “parents written consent” is not usually listed as inclusion criteria. Instead, you can add a separated sentence like the following “Informed consent was obtained from the parents/guardian of all the children enrolled in the study.” This goes along the Stage I – preparation section

5. There are several language mistakes in the paper. You should have it corrected by a language expert.

6. Lines 198-199. Can you justify the reason why you use the variables of height and width of the ellipse? Instead of those two, in order to analyse the COP in the anterio-posterior and medio-lateral direction, is there a reason why you did no use COP velocity?

7. Lines 202 -218. What you describe as a qualitative assessment is wrong. You have used quantitative measures (COP velocity) and chose three ranges to compare them. Have you based your ranges on any previously published paper? If not, what is the reasoning behind allocating certain ranges to low, average, high postural stability?

8. Line 235-243. Can you justify the statistical analysis used for your variables? Why did you use Chi-Square statistics?

9. Your discussion includes a lot of information from different papers and researchers but little from your own study. You are not addressing the results from each of your five parameters and how each of them are relevant to postural control.

Minor issues

1. Lines 120-121. By this sentence it looks like you say that adult levels of postural control are attained at 6 years of age. Studies have shown that adult levels of postural control are reached much later that 6 years old (check article below). At 6 years though, children do have mastered adult levels in some specific aspects of postural control. You should speficy more or rephrase.

Barozzi S, Socci M, Soi D, Di Berardino F, Fabio G, Forti S, et al. Reliability of postural control measures in children and young adolescents. Eur Arch Otorhinolaryngol. 2014 Jul;271(7):2069–77.

2. Line 136. Energy is not a physical ability, please rephrase.

3. Line 140. “mount of sway” not sways.

4. Line 164. In your Initial medical check-ups you assess general health as an exclusion criteria and that does not appear listed in the exclusion criteria previously mentioned. Please clarify whether this was or not another exclusion criteria.

5. Line 180-181. The sentence is confusing, please check language grammar.

6. Lines 188-199. You mention three sway parameters and then you list 5: COP area, ellipse area, COP path, COP velocity, height of ellipse, width of ellipse

7. Review the bibliography. There are some mistakes on numbers:

5: there is a coma after the title, it should be a point.

19: Remove “dos Santos Cardoso de” for the first author, it is repeated (Sa, C.), the title starts with “Development” and not “Developmental”.

24: There is a coma after the authors, it should be a point.

Reviewer #2: The authors employed standard methods and analysis to quantify the postural sway of 5-year-old boys and girls during a task where they tried, supposedly, to stay as still as possible for 30 s. The data collection and analysis seem to be correct in the sense they are not very different than the ones used in other studies in the area.

The main problem with the present study is that the authors try to use these measurements to quantify postural stability and use that to differentiate the degree of stability between girls and boys.

After the authors tried to interpret their results with more postural-control centered explanations, they laconically recognize that "The postural stability of girls is better because boys seem to be less attentive.".

So, I question the significance of the results if one can trivialize them by simply stating that they were obvious since a 5-year-old boy can't stand still. If the authors still want to study the stability of the postural control in children, they should at least provide an independent measure of attention.

At the current state, this study provides very limited novel information.

The authors declared that "all data are fully available without restriction", but I couldn't find any information about where to access the data.

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Reviewer #1: No

Reviewer #2: No

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1 Nov 2019

We would like to thank for the review and comments regarding our manuscript titled “Postural stability of 5-year-old children with different levels of body height” written by Magdalena Plandowska, Małgorzata Lichota and Krystyna Górniak.

Thank you for a detailed analysis of our work and for all the comments which will undoubtedly lead to increasing the value of this article.

The changes suggested by the Reviewers have been enlisted below. In order to facilitate the assessment of the changes made in the revised version of the manuscript, they have been highlighted in grey. We hope that the changes will be satisfactory for the Reviewers and will make the paper methodologically correct and interesting for the readers.

Response to Reviewer # 1

Major issues

1. Regarding the comment: There is over one page regarding basic information about the COP and how to obtain it.

I agree that the Introduction section contains too much basic information about the COP. As suggested, this part has been reduced (lines 79-90).

2. Regarding the comment: You are using very old references.

Thank you for information about publications. References have been changed.

3. Regarding the comment: You are using the term “levels” for postural stability and for body height. I would rather suggest using greater/worse/more/less/higher/lower instead of levels since there are no established levels of either.

Thank you for your comment regarding the term “levels” for postural stability and for body height. I agree that the there are no established levels of either. I have taken them into account. According to the reviewer’s suggestion, the term “levels” has been removed. The title has been reedited. Instead of the term “levels”, I decided to use better/worse postural stability.

4. Regarding the comment: “parents written consent” is not usually listed as inclusion criteria.

Thank you for your comment. We have taken it into account. The Participants section has been reedited (lines 130-137).

5. Regarding the comment: There are several language mistakes in the paper.

Thank you for your comment. As suggested, the article has been edited by a native speaker.

6. Regarding the comment: Can you justify the reason why you use the variables of height and width of the ellipse?

The reason is the limitations of the measuring platform. The equipment does not provide detailed values of COP velocity in anterior-posterior (AP) and medial-lateral (ML) directions. Therefore, in order to analyse the COP in the anterior-posterior and medial-lateral direction, I used length of ellipse in the anterior-posterior direction (LoEAP, height of the ellipse) and length of ellipse in the medial-lateral direction (LoEML, width of the ellipse). I think that the selected parameters properly describe shifts of the COP and the surface of the ellipse (lines 173-186).

7. Regarding the comment: What you describe as a qualitative assessment is wrong. Have you based your ranges on any previously published paper? If not, what is the reasoning behind allocating certain ranges to low, average, high postural stability?

Thank you for your comments. A big number of study participants (435) made it possible to determine the levels of postural stability on the basis of the available methods of descriptive statistics. I thought that the selected criteria of the level of postural stability may constitute a reference to the assessment of postural stability in children from this age group. But I have not based ranges on any previously published paper. I decided to remove a qualitative assessment. Therefore, the section Stance analysis (lines 173-186) and the section Results were reedited (lines 215-240).

8. Regarding the comment: Can you justify the statistical analysis used for your variables? Why did you use Chi-Square statistics?

The Shapiro-Wilk test was used to analyze whether the variables had a normal distribution. Data normality was rejected, so the Mann-Whitney U test was used to examine differences between girls and boys.

The Chi square test was used to identify significant differences in the percentage of children with different postural stability. I decided to remove qualitative assessment, so the Chi square test was removed, too.

9. Regarding the comment: Your discussion includes a lot of information from different papers and researchers but little from your own study. You are not addressing the results from each of your five parameters and how each of them are relevant to postural control.

Thank you for your comments. The section Discussion has been reedited.

Minor issues

1. Regarding the comment: By this sentence it looks like you say that adult levels of postural control are attained at 6 years of age. You should speficy more or rephrase.

The reviewer`s suggestion has been taken into account in the manuscript. This sentence has been corrected (lines 105-106).

2. Regarding the comment: Energy is not a physical ability, please rephrase.

It has been corrected (line 120-121).

3. Regarding the comment: “mount of sway” not sways.

Thank you for your comment. It has been corrected according to the suggestion (line 125).

4. Regarding the comment: In your Initial medical check-ups you assess general health as an exclusion criteria and that does not appear listed in the exclusion criteria previously mentioned. Please clarify whether this was or not another exclusion criteria.

Thank you for this comment. Bad general health was another exclusion criterion (lines 132-134).

5. Regarding the comment: The sentence is confusing, please check language grammar.

Thank you for this comment. This sentence has been reedited (166-168).

6. Regarding the comment: You mention three sway parameters and then you list 5: COP area, ellipse area, COP path, COP velocity, height of ellipse, width of ellipse.

Thank you for this comment. A technical error.

7. Regarding the comment: Review the bibliography. There are some mistakes.

Thank you for your comment. The bibliography has been corrected.

Response to Reviewer #2:

Thank you for reading our article. According to the comments of the reviewers, the manuscript has been corrected.

Submitted filename: Response do Reviewers.docx

Click here for additional data file.

19 Nov 2019

PONE-D-19-20547R1

Postural stability of 5-year-old girls and boys with different body heights

PLOS ONE

Dear Mrs Plandowska,

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.

Reviewer 1 saw your original submission, and is satisfied with your revisions. Reviewer 2 is new. Reviewer 2 raises a number of minor issues that could benefit from clarification. Please make the requested changes, and I will be happy to accept your paper for publication in PLOS ONE.

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We look forward to receiving your revised manuscript.

Kind regards,

Thomas A Stoffregen, PhD

Academic Editor

PLOS ONE

Additional Editor Comments (if provided):

Reviewer 1 saw your original submission, and is satisfied with your revisions. Reviewer 2 is new. Reviewer 2 raises a number of minor issues that could benefit from clarification. Please make the requested changes, and I will be happy to accept your paper for publication in 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 #3: (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 #3: Yes

**********

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

Reviewer #1: Yes

Reviewer #3: 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 #3: 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 #3: Yes

**********

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: After rereading the changes, I have found that you have addressed all the points that I mentioned on my first review. The large sample was already valuable and now it is well written and methodologically sound from my point of view.

Reviewer #3: Page 2, line 31

“Gender” is utilized throughout the paper, but the proper term for what was studied is “sex.”

Page 7, line 167

Other experiments of postural sway have utilized marked stance widths. Were children told to stand “normally”? Later (page 12, line 272) states that girls had a smaller stance, which indicates to me that the participants were not given a “set” width. A more detailed explanation of methods on page 7 is needed.

Page 9, line 197

The phrase “statistically significant” indicates that some form of analysis was used, but this doesn’t say what analysis. Mann-Whitney U is stated later, but proper reporting is (U = xxx, p=0.02). Clarity is needed here.

Page 10, line 220

This also needs to proper statistical reporting (U=xxx, p=.xxx). This is seen throughout the rest of the manuscript.

Page 14, line 312

This paragraph seems like it should be in the into, not the discussion.

Page 14, line 315

I am confused on why this paragraph opens up with “environment and socio-cultural factors,” and then presents no discussion of these factors.

What is discussed in this section seems like it would fit in the introduction as motivation.

A discussion of said environment and socio-cultural factors would be appropriate here, and would help provide insight into the differences being seen.

Overall, I found this paper to be a worthy contribution to the scientific community. My main issue is that the paper has several minor issues that can be revised without too much trouble. The most concerning of these is the discussion, which I feel contains information that should have been used to motivate the study in the introduction. This section limits the impact the article has by reflecting on the findings of others, instead of discussing the study's findings to their full extent.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: Yes: Roberto Izquierdo-Herrera

Reviewer #3: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files to be viewed.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email us at figures@plos.org. Please note that Supporting Information files do not need this step.

7 Dec 2019

Thomas A Stoffregen, PhD

Academic Editor

PLOS ONE

We would like to thank for the review and comments regarding our manuscript titled “Postural stability of 5-year-old girls and boys with different body heights” written by Magdalena Plandowska, Małgorzata Lichota and Krystyna Górniak.

Thank you for a detailed analysis of our work and for all the comments which will undoubtedly lead to increasing the value of this article.

The changes suggested by the Reviewer 3 have been enlisted below. In order to facilitate the assessment of the changes made in the revised version of the manuscript, they have been highlighted in grey. We hope that the changes will be satisfactory for the Reviewer and will make the paper methodologically correct and interesting for the readers.

Response to Reviewer # 1

Thank you for a detailed analysis of our work and for all the comments which undoubtedly leaded to increasing the value of this article.

Response to Reviewer # 3

1. Regarding the comment:“Gender” is utilized throughout the paper, but the proper term for what was studied is “sex.”

Thank you for your comment. We have taken it into account.

2. Regarding the comment: Page 7, line 167 - Other experiments of postural sway have utilized marked stance widths. Were children told to stand “normally”? Later (page 12, line 272) states that girls had a smaller stance….

Thank you for your comment. The sentence (page 12,line 279-281) has been corrected.

3. Regard the comment: Page 9, line 197 - The phrase “statistically significant” indicates that some form of analysis was used, but this doesn’t say what analysis. Mann-Whitney U is stated later, but proper reporting is (U = xxx, p=0.02).

Thank you for your comment. It has been corrected according to the suggestion.

4. Regard the comment: Page 10, line 220 - This also needs to proper statistical reporting (U=xxx, p=.xxx). This is seen throughout the rest of the manuscript.

Thank you for your comment. We have taken it into account.

5. Regard the comment: Page 14, line 312 - This paragraph seems like it should be in the into, not the discussion.

Thank you for your comment. This paragraph has been included in the Introduction (page 5-6, line 118-121).

6. Regard the comment: Page 14, line 315 - I am confused on why this paragraph opens up with “environment and socio-cultural factors,” and then presents no discussion of these factors. What is discussed in this section seems like it would fit in the introduction as motivation. A discussion of said environment and socio-cultural factors would be appropriate here, and would help provide insight into the differences being seen.

Thank you for your comment. As suggested, this paragraph has been reduced (page 14, line 317-334) and part of it has been included in the Introduction (page 6, line 116-127).

Yours sincerely,

Magdalena Plandowska

Jozef Pilsudski University of Physical Education in Warsaw,

Faculty of Physical Education and Health, Biala Podlaska, Poland

Submitted filename: Response do Reviewers.docx

Click here for additional data file.

13 Dec 2019

Postural stability of 5-year-old girls and boys with different body heights

PONE-D-19-20547R2

Dear Dr. Plandowska,

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

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With kind regards,

Thomas A Stoffregen, PhD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

19 Dec 2019

PONE-D-19-20547R2

Postural stability of 5-year-old girls and boys with different body heights

Dear Dr. Plandowska:

I am 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.

If your institution or institutions have a press office, please notify them about your upcoming paper at this point, to enable them to help maximize its impact. If they will be preparing press materials for this manuscript, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

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Thank you for submitting your work to PLOS ONE.

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on behalf of

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Academic Editor

PLOS ONE