Introduction:
A sedentary lifestyle causes severe changes in the functioning of the trunk muscles, pelvic girdle and lower extremities in the population of healthy people. Understanding the synergies of muscles active while maintaining a standing position may, in this aspect, provide clinically helpful information for kinesiotherapy. There is little data on the assessment of synergistic muscles activity of the lower extremities using non-invasive polyelectromyography recorded with surface electrodes (sEMG) in a relaxed standing position, and due to the tendency of decreasing activation the proximal muscles, it can be expected that the previously developed movement patterns may have changed.

Aim:
This pilot study aims to verify the activity of the lower extremities’ most crucial synergistic muscle groups engaged in posture maintenance in a population of healthy people using sEMG.

Material and Methods:
In a group of 14 healthy volunteers (7 women and 7 men), sEMG examination of the gluteus maximus (GM), rectus femoris (RF), tibialis anterior (TA), and dorsal foot extensors (EXT) was performed in 6 positions; resting in standing and lying, GM and RF maximal contraction in standing and lying and TA and EXT maximal contraction in standing and lying. A survey on daily activity was carried out among healthy volunteers. The output parameter of the sEMG tests was the mean value of the amplitude measured in microvolts.

Results:
The subjects spent an average of 8 hours a day in a sitting position and 5.5 hours a day in a standing position. In the resting during standing position, the study of the electromyogram amplitude parameter showed a significant change in the involvement of the distal muscles of the lower extremity over proximal muscles (TA mean 67.5 μV; EXT mean 33.22 μV vs. GM mean 21.4 μV; RF mean 26.95 μV). The greatest tendency in changes of the lower extremities’ synergistic muscle function can be observed in the disproportion of proximal and distal muscle activity by about 60% in maintaining a relaxed standing position.

Conclusions:
The gluteal muscles show dysfunctional changes resulting from the sedentary lifestyle; they are no longer synergistic with the rectus femoris muscles in relaxed standing. Pilot studies showed no significant disturbance of the synergy of proximal and distal muscles during the attempt of their maximal contraction in the supine position. A significant disproportion in activation of the synergistic distal muscles of the lower extremities in the standing position was demonstrated.