The aim of this study was to determine whether quiet standing postural sway (represented by the anterior-posterior and medial-lateral COP mean velocities under eyes-open and eyes-closed conditions) was different between young female artistic and acrobatic (carrying out the role of the “tops”) gymnasts. We also searched for correlations between the gymnasts’ postural sway velocities and their training experience, ages, body heights, body masses, BMI percentiles, and maturity offsets. The nonsignificant between-group differences observed in the postural sway velocities suggest similar postural steadiness in the artistic and acrobatic gymnasts under both visual conditions. However, it is worth mentioning that on average, artistic gymnasts swayed slower in the anterior-posterior direction under eyes-open conditions and the difference between the two groups (effect size) was medium. As expected, visual deprivation had an impact on the increase in postural sway velocities in both artistic and acrobatic gymnasts. In turn, as was hypothesized, the results of the correlations were not always analogous for the two groups.
The present study indicates that the longer training experience of young adolescent artistic gymnasts was strongly related to their lower anterior-posterior postural sway velocity (better postural steadiness) under eyes-open conditions. It is possible that the artistic gymnasts’ specific high-intensity training regimen [26, 27] contributed to such relationship. One of the goals in artistic gymnastics training is to achieve a perfectly steady bipedal posture (“stuck landing”) in the final phase of aerial routines. Among the most important muscle groups engaged in the “stuck landing” are foot plantar and dorsal flexors [35, 36]. Because these muscles also play the greatest role in anterior-posterior quiet standing postural control , it is possible that longer practicing and perfecting of the “stuck landing” also resulted in improved anterior-posterior postural steadiness. The relationship between the length of the training experience and the anterior-posterior postural sway velocity was only observed during trials with normal visual conditions, possibly because gymnasts practice their routines with their eyes open, and visual information is used to enhance the stability of the landing .
In turn, this study indicates that in the acrobatic gymnasts (practicing as “tops”) the length of their training experience was not reflected by specific changes in their quiet standing postural sway. Although the performance level of the young adolescent gymnasts in both groups was national, training experience in the acrobatic gymnasts was shorter (the mean length of training experience in the acrobatic gymnasts was 3.3 years and it was 4.8 for the artistic gymnasts). It is therefore possible that the training experience of the acrobatic gymnasts was not long enough to influence the characteristics of their quiet standing postural sway. Similarly, in 6–8-year-old children who practiced artistic gymnastics on average for 2.75 years, the duration of training experience was poorly related with static balance assessed with Stork Balance Stand test .
The shorter duration and lower frequency of the acrobatic gymnasts’ training sessions as well as their specific training regimen might have influenced the results as well. It may be considered that for the “top” acrobatic gymnast, it is not as difficult to maintain a steady bipedal posture during the final phase of the aerial routine (the “stuck landing”) as it is for the artistic gymnast because during this phase, the “top” gymnast is being safeguarded by the “base” gymnast (s). Perhaps practicing landing with the external support of the partner gymnast (s) also contributed to nonsignificant relation between the duration of the training experience and the postural sway in the acrobatic gymnasts.
The present study indicates that in young adolescent artistic gymnasts, not only a longer training experience, but also older age, greater body mass, body height, and biological maturity were strongly or very strongly related to better anterior-posterior postural steadiness. Since in this group the length of training experience, age, and anthropometric factors were also positively correlated with each other, it appears that the relationship between training experience and anterior-posterior steadiness in the artistic gymnasts went hand in hand with their maturation and physical development. Concomitantly, in the non-athletes a poor correlation between the anthropometric measures and postural steadiness was observed. This allows the authors to conclude with greater certainty that the result of the strong relationship between the artistic gymnasts’ training experience and their anterior-posterior steadiness was not coincidental.
Similar to the results obtained for the non-athletes, the age, body height, and maturity offset of the “top” acrobatic gymnasts were poorly related to their postural steadiness. Unlike the artistic gymnasts, the age of the acrobatic gymnasts was poorly correlated with their height, which suggests that older acrobatic gymnasts were not necessarily those who were taller. Although there were nonsignificant age differences between the gymnasts of the two disciplines, none of the “top” acrobatic gymnasts represented the age of 13 years. Concomitantly, the “top” acrobatic gymnasts were characterized by a lower body height (by 7 cm on average) compared to that of the artistic gymnasts, which suggests that having a low height was one of the strong determinants of their high (national level) performance. In the group of “top” acrobatic gymnasts, lower standard deviations from mean age, height, or maturity offset were also observed, indicating less intra-group variability. It is possible that too much intra-group similarity prevented the demonstration of a stronger association between these measures and postural sway velocity. However, this study indicates, as in the artistic gymnasts, that the greater body mass of the acrobatic gymnasts was strongly related to their better anterior-posterior postural steadiness. Interestingly, in the acrobatic gymnasts the association was observed regardless of the visual conditions. In the eyes-closed trials, greater body mass was also related to better medial-lateral steadiness. These results may suggest that when vision was not available, the acrobatic gymnasts who demonstrated greater body mass used their redundant system more effectively in the control of quiet standing. The above mentioned results are not in agreement with the investigation on dynamic stability in pre- and postpubertal female gymnasts practicing trampoline. That study demonstrated a poor correlation between gymnasts’ body height and mass and their dynamic body sway frequencies acquired while standing on a seesaw platform . In another study of younger children (aged 6–8 years) practicing artistic gymnastics, static balance assessed with the simple balance test was negatively correlated with their body height and positively correlated with their body mass . The comparison of the results of the present investigation with those studies and the interpretation of their discrepancies would be unjustified because the divergence in the sample characteristics and research methodology is too large.
In the present study, the acrobatic gymnasts’ higher BMI percentiles were also strongly related to better anterior-posterior postural steadiness under normal visual conditions and moderately related to better anterior-posterior and medial-lateral steadiness under visual deprivation conditions. Body mass index is a function of mass and height; however, the BMI percentiles for children are age- and sex-specific. Therefore, this study indicates that in some of the acrobatic gymnasts, not only greater body mass but also higher values of the body mass and square of the body height ratio specific to their age and sex were related to better overall postural steadiness. Interestingly, the artistic gymnasts’ BMI percentiles were poorly related to their postural steadiness. Based on these study results, the authors are not able to explain why artistic gymnasts and acrobatic gymnasts training as “tops” demonstrated different strengths of association between postural steadiness and body mass or BMI percentiles. Further research is necessary to investigate this phenomenon. Perhaps a deeper evaluation of postural sway variability and regularity (based on sample entropy assessment) or stabilogram decomposition into rambling and trembling components will make the interpretation of the strength of such correlations possible.
As it has been already mentioned, this study shows that the anthropometric measures of age-matched non-athletes were poorly related to their postural steadiness. These results are similar to the studies on larger non-athlete populations which examined 57 children age 7–18  and 152 children age 7–12 . According to these studies, the children’s postural stability was poorly correlated with their body mass and BMI, and it was poorly to weakly positively correlated with their body height. However, a weak to moderate positive correlation was observed between age and postural stability [9, 10]. This suggests that in order to detect the impact of age on postural sway characteristics in non-athlete children, a larger sample size with a larger age range is needed.
Although the young untrained females in the present study demonstrated age and biological maturity similar to that of the gymnasts, they were characterized by their greater body height, mass and BMI percentiles, and larger diversity of their anthropometric characteristics. It is possible that if the group is more diverse in regard to body proportions and composition (the percentage of muscle and fat tissue), the demonstration of the relationship between anthropometric measures and postural steadiness becomes impossible.
The results of this study should be considered with caution because of the relatively small sample size (the recruitment of larger number of 10–13-year-old, national level, female gymnasts in the Upper Silesian region was not possible). On the other hand, the strength of this study are rigorous inclusion and exclusion criteria resulting in the relatively large homogeneity of the selected groups of young adolescent female gymnasts in regard to their somatotype.