The results of our study demonstrate that there are significant correlations between the balance parameters based on frontal plane deflections between adult relatives. Together with the results provided in an accompanying paper (Bezulska et al., 2018), these observations extend what is known about correlations within families with respect to motor skills related to proprioception from muscle receptors and vestibular organs.
Before the study we supposed that correlations in balance between fathers and sons could result from genetic and lifestyle-related factors (social factors, habits, physical activity) (Kovalek et al., 2019, Moreno-Segura et al., 2019, Panou et al., 2018). Our research showed that there was a significant correlation between the lifestyle of fathers and their sons. However, there were no significant correlations between the fathers lifestyle and balance and between the sons lifestyle and balance. Given that it seems that the ability to maintain balance predominantly is genetically determined.
There are two possible reasons for the presence of correlations in balance parameters among relatives. First, it is possible that functional efficiency of the sensory system associated with balance (i.e., vestibular organ and/or muscle spindles) is hereditary. Second, it is possible that the functional efficiency of CNS structures (mainly of vestibular nuclei, cerebellum, and spinal cord) that are active while maintaining balance (Welch and Ting, 2014) has a genetic component.
The range of the equilibrium parameters that we investigated increased after prolonged running. It is known that muscle spindle afferents associated with the control of body position are modulated during activity. Moreover, muscle length changes during consciously performed physical activity, as well as during automated maintenance of vertical posture (Winter et al., 2005; Ansems et al., 2006; Allen et al., 2007, Allen et al., 2010); this probably modulates the activity of muscle receptors. These mechanisms may partly explain the observed deterioration in balance while under the influence of fatigue.
Physical exercise and fatigue did not affect the examined correlations, although the studied balance parameters increased (Figs. 1–5). This observation is in concordance with data from the literature (Brito et al., 2012; Chaubet and Paillard, 2012; Arliani et al., 2013). The correlation coefficients increased, most likely as an effect of enlargement of the ranges of the analysed parameters and the similar degree to which fatigue influenced both fathers and sons. On the other hand, the increase in tested values may be explained by post-fatigue systemic changes (e.g., increased heart rate, uneven breathing, and discomfort associated with severe sweating), as well as by altered muscle receptor activity during exercise or slow adaptation of receptors after physical activity (Allen et al., 2010; Walsh et al., 2004, Walsh et al., 2010).
In the described experiments, the subjects maintained steady footing on the platform; thus, any movement of the body caused tilting of the head in different directions in the horizontal plane. However, the significant correlations found in the present study concerned parameters related to movements in the anteroposterior axis, most probably due to the lateral support of the body on both feet. The dominance of deflections in the anteroposterior axis of COPP has been confirmed in numerous studies (Błaszczyk and Orawiec, 2011). Many authors have stressed the significance of the plane in which the movement occurs (Ansems et al., 2006; Allen et al., 2007; Allen et al., 2010; Bekrater-Bodmann et al., 2012), which is associated with differences in proprioceptive information that are dependent on gravity (Winter et al., 2005).
In many sports the ability to maintain balance directly affects the sport results. Our results suggest that the ability to maintain equilibrium is hereditary, that conclusion can be useful to sport selection process in some disciplines, e.g. in shooting, archery. Moreover, the results of our study indicated that physical exercise and fatigue did not affect the examined correlations in measured balance parameters between fathers and their sons (values of correlation coefficients remained statistically significant). Thus, our results may be useful also to sport selection process, e.g. biathlon, ice skating, gymnastics.