## 4 Discussion
As aging is a continuous process knowing about the raising body sway might help the understanding on health risks such as fall and fractures and motivate women to train systematically in order to prevent or to slow down the negative impact. Accordingly, the values for the ellipse area published by [PERSON] et al. [11] of 70 mm\({}^{2}\) and 72 mm\({}^{2}\) are smaller than the values measured in this study [21]. This discrepancy is because the group of subjects measured by [PERSON] et al. [11] had a wide age range of 11-69 years, with only 30 persons of these 431 subjects belonging to the age range of 50-60 years. Furthermore, both genders were represented in the group of 30 subjects. Therefore, the age-related differences [5,39,40,41,42,43] in the ellipse area can be explained by the predominance of younger subjects in the subject collective. This effect is due to the multifactorial changes of age [4,5,38,42,43,44,45,42]. Thus, the higher values of the ellipse area in the present study are to be expected in a differentiated consideration of the age group of 50-60-year-olds. The subjects of the present study had an average BMI of 25.02 \(\pm\) 4.55 kg/m\({}^{2}\) and were, therefore, on average, in the preadipose stage according to the WHO classification [29]. It should be noted, however, that the limit to the preadipose stage was exceeded by the test subjects by 0.02 kg/m\({}^{2}\). The German Federal Statistical Office provides an average BMI of 25.2 kg/m\({}^{2}\) for women in the 50-55 age group and 25.6 kg/m\({}^{2}\) for women in the 55-60 age group, thus, the selected group of test subjects was, in fact, even below the stated German average [26]. In a different study of the Robert Koch Institute on the representative data for height, weight and BMI of the German population from 2013, present subjects were on average 3 kg/m\({}^{2}\) lighter [46]. With regard to the influence of BMI, the statistical analysis showed no significance for the postural fluctuations (\(p\) > 0.05), neither for the absolute BMI values nor when differentiating into different groups according to the WHO classification [29]. Only a descriptive trend for sagittal sway was found: a BMI > 30 led to increased sway compared to normal-weight subjects (normal BMI: 15.67 mm; obese BMI: 19.17 mm). The results of the present study regarding a lack of significant (\(p\) > 0.05) association between BMI and balance control are confirmed by the studies of other investigators [35; 47; 48]. Due to the weak effect size of the change in body sway, this finding should be interpreted as a trend rather than as clinically relevant. Accordingly, even without subjective, pathological information, the balance ability slowly decreases over the course of life. The use of BMI as a criterion has limitations, as there is no sufficient differentiation as to whether the person in question is, for example, overweight or merely heavily muscled. Nevertheless, the authors deliberately chose BMI as a measure because it facilitates comparability with other studies, since BMI is still a commonly used criterion. In addition, the calculation of BMI is based on the self-report of each participant. However, if the examiner had any doubts about the accuracy of the self-report, a scale or centimeter measure was used to check the information. This was only the case three times. [PERSON] et al. [49] also confirmed that the extent of the fluctuation in the anterior-posterior direction does not increase significantly (\(p\) > 0.05) in obese persons compared to normal weight persons, but only tends to increase (sagittal fluctuation: normal weight 21 mm; obese 21.6 mm) and justified this with a functional adaptation of the control mechanisms of the upright posture. [PERSON] et al. [50] postulated that the center of pressure shifts anteriorly with increasing BMI and, thus, to a greater distance from the ankle [50; 51]. Possible causes for the lack of influence of BMI on balance control under static conditions are sometimes manifold.