Correlations in parameters of balance between fathers and their adult sons

Background : The literature data suggest that balance control is genetically determined, however the data are inconsistent with respect to correlations in balance parameters among adult relatives. Therefore, the aim of the present study was to identify correlations between fathers and their adult sons in chosen balance parameters. Moreover, we tested how the relationships in balance between fathers and their adult sons change following fatigue. Methods: The balance parameters were measured twice: before and immediately after the fatigue procedure (treadmill running to exhaustion) with the pedographic platform in two groups of relatives and correlated for 30 pairs father-adult son. Results: The positive significant correlations were found for parameters describing deflection in the sagittal plane: the average deflection of center of pressure progression (COPP) and average value of COPP velocity in sagittal plane as well as the average value of velocity of COPP, the length of COPP trajectory and the surface area of the trajectory covered by COPP, both before and after the fatigue procedure. Conclusions: In summary, our study found numerous correlations in balance parameters related to deflection in the sagittal plane between fathers and their adult sons. These correlations were not abolished by fatigue. Our results suggest that the ability to maintain balance is influenced by genetics. This conclusion can be useful in many sports in which the ability to maintain balance influence on sports score.


Abstract
Background : The literature data suggest that balance control is genetically determined, however the data are inconsistent with respect to correlations in balance parameters among adult relatives. Therefore, the aim of the present study was to identify correlations between fathers and their adult sons in chosen balance parameters. Moreover, we tested how the relationships in balance between fathers and their adult sons change following fatigue.
Methods: The balance parameters were measured twice: before and immediately after the fatigue procedure (treadmill running to exhaustion) with the pedographic platform in two groups of relatives and correlated for 30 pairs father-adult son.
Results: The positive significant correlations were found for parameters describing deflection in the sagittal plane: the average deflection of center of pressure progression (COPP) and average value of COPP velocity in sagittal plane as well as the average value of velocity of COPP, the length of COPP trajectory and the surface area of the trajectory covered by COPP, both before and after the fatigue procedure.
Conclusions: In summary, our study found numerous correlations in balance parameters related to deflection in the sagittal plane between fathers and their adult sons. These correlations were not abolished by fatigue. Our results suggest that the ability to maintain balance is influenced by genetics. This conclusion can be useful in many sports in which the ability to maintain balance influence on sports score.

Background
Balance and human body orientation are dependent on multiple sources of afferent and efferent information about ongoing and intended patterns of movement and posture.
Exposure to unusual forces and patterns of sensory feedback alters the normal relationship between patterns of alpha and gamma activation of antigravity muscles, muscle spindle activity, and movements of the body, which may evoke illusory feelings of motion and balance disorders (Lackner and Graybiel, 1984;Young, 2003). Maintaining balance is a process that involves multiple receptors; namely, the vestibular system and muscle proprioceptors (mainly muscle spindles in extensors). In addition, vision plays a part in posture maintenance (Gandevia, 1996;Gandevia et al, 2006;Chalmers, 2004;Proske, 2005;Wang et al., 2012). In the central nervous system (CNS), the brain stem structures (mainly vestibular nuclei) and cerebellum are involved in posture control.
Equilibrium is one of the most important elements of each motor task, both for maintenance of stable body position (static equilibrium) as well as during movement (dynamic equilibrium) (Comerford and Mottram, 2001). Thus, the ability to maintain balance is a factor that influences motor skills and plays an important role in the prevention of injuries.
Muscle fatigue is known to modulate the proprioceptive and kinesthetic properties of the joints; it increases the discharge threshold of muscle spindles, weakens afferent feedback, and changes somatosensory input, thereby inducing deficits in neuromuscular control Deterioration of balance has also been observed in knee extensor fatigue caused by electrical stimulation (Chaubet and Paillard, 2012). Other studies have confirmed the impact of fatigue of the lower limbs on proprioception of the knee and injury incidence, and it is believed that disorders of neuromuscular control are the main mechanism (Hiemstra, et al., 2001).
Motor skills, including maintaining of balance and motor coordination, are a result of interactions between genetic factors and the external environment (Bouchard et al. 1997;Molly et al., 2009;Rankinen et al., 2006), although this issue is not yet completely understood. Many authors have posited that at least some coordination skills have a genetic basis (Frederiksen et al., 2002;Tiainen et al., 2004). The results of tests carried out on pairs of twins showed similarities in accuracy of movement, as well as in the ability to repeat the target force (Lyakh, et al., 2007). It should be emphasised that various testing methods can produce different results. In family studies based on the EUROFIT method ("flamingo balance"), which compared balance parameters between parents and their children, there was no significant correlation when the results of fathers and mothers were compared to the results of their sons and daughters (Jaworski et al., 2010). However, the paper did not detail how the measurements were made. The lack of correlation in this study might be due the comparison of adult parents with their children, whose motor skills were still under development as they matured.
Information from the literature is inconsistent with respect to correlations in balance parameters among adult relatives. Therefore, the aim of the present study was to identify correlations between fathers and their adult sons in basic balance parameters: dominant direction and deflection value, speed of movement of center of gravity, and size of area defined by trajectory. Balance measurements were made both before exercise and under the influence of fatigue caused by running until exhaustion.

Participants
Thirty pairs of fathers and adult sons were selected. The mean basic characteristics of the fathers were age 49.6 ± 5.3 years, height 176.1 ± 4.6 cm, and weight 87.1 ± 9.6 kg. The mean basic characteristics of the sons were age 23.3 ± 3.7 years, height 179.9 ± 6.8 cm, and weight 78.6 ± 13.2 kg). All individuals were medium-level physically active, not in training for any sport, and healthy. None of the participant had contraindications for participation in the experiment, and their good health was confirmed by a medical doctor, who also supervised the experimental protocol.

Balance test
The

Fatigue procedure
After the balance test, each participant performed a running test on a treadmill Trackmaster TM310 (USA). During this test, the maximal oxygen uptake (VO 2 max) was determined. Breath-by-breath oxygen uptake was continuously recorded with the Oxycon Mobile ergospirometric system (Viasys Healthcare, Germany). Heart rate was continuously recorded during the test with the portable heart rate telemetry device Polar Sport Tester (Finland). The test was incremental; all participants started at a 4.0 mph running speed, which was increased by 0.5 mph every 2 minutes until the maximal level of recorded parameters was achieved. When the participant could not continue the test because of fatigue, the test was stopped. Three criteria for task termination were taken into consideration: respiratory exchange ratio >1.1, oxygen consumption plateau despite of running speed increase, obtaining maximum heart rate in relation to age of participant.
When two from three mentioned above criteria were met and participant was not able to run the fatigue test was completed. Immediately after the fatigue procedure, the participants repeated the balance test according to the methodology described above.

Statistical analysis
A two-sample independent t-test was used to determine the significance of differences between the parameter measurements obtained from fathers and sons. To investigate the influence of fatigue on the analysed parameters within one group, the paired sample t-test was used. Because for all studied properties a normal distribution of data was confirmed, Pearson correlation coefficients were determined for selected variables achieved by fathers and their sons. P values of <0.05 were considered significant.

Results
The average deflection of COPP in the front-rear direction (Wx) was 4.9 ± 1.9 mm in the group of fathers and 4.5 ± 1.9 mm in the group of sons before exercise. Later, due to fatigue, both values increased accordingly to 6.7 ± 3.7 mm and 7.3 ± 3.5 mm in the father and son groups, respectively. The correlation in Wx between the fathers and sons was significant both before and after fatigue (Figure 1).
(figure 1 about here) Deflection of COPP in the right-left direction (Wy) in the group of fathers was 5.7 ± 1.8 mm before exercise and 8.6 ± 4.4 mm after exercise, while it was 4.9 ± 2.0 mm for sons before exercise and 10.2 ± 8.4 mm after exercise. There were no significant correlation between the results for fathers and their sons (r = -0.11 and r = 0.19 before and after exercise, respectively).
There was a positive correlation in the average velocity of COPP (aq) along both axes between fathers and sons, and the correlation coefficients before and after exercise were significant ( Figure 2). Significant correlations were also observed for the average velocity of COPP along the x axis (asx), both before and after exercise (Figure 3). In contrast, correlations of COPP velocity in the frontal plane (asy) were low and statistically insignificant. A significant correlation was also found for path length (pl) (Figure 4) and 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.

Conclusions
Our study found numerous correlations in balance parameters related to deflection in the sagittal plane between fathers and their adult sons. These correlations were not abolished by fatigue. Our results suggest that the ability to maintain balance is influenced by genetics.

Declarations
Ethics approval and consent to participate All participants provided written informed consent to participate in the study, and all procedures were approved by the local ethical committee (Ethics Committee at the Adam Mickiewicz University in Poznan, Poland), with approval based on the Declaration of Helsinki.

Consent for publication
The manuscript does not contain any individual person's data in any form.

Availability of data and materials
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests Funding The authors declare that did not receive financial support to conduct the research.
Authors' contributions MN -performed the research in laboratory and was a major contributor in writing the manuscript AB -was responsible for subjects recruiting and performed the research in laboratory ZA-cooperation in study design, statistical analysis JC -was responsible for the design of the study and was a major contributor in writing the manuscript Figure 1 Correlations in the mean deflection center of pressure in the direction of the sagittal plane (Wx) between fathers and their adult sons, both before (a) and after (b) exercise. Each point corresponds to data from one father-son pair.
Equations for the regression lines appear over the plot. * Correlation significant