Effect of voluntary muscle contraction on postural stability in healthy adults

Introduction
Postural control is a complex system that combines many subcomponents. The central nervous system's connection with the muscular system allows to execute the voluntary movements and provides appropriate tonus and contractions of postural muscles. The aim of this study was to assess the effect of voluntary muscle contraction on the stability of standing posture.

Material and methods
Seventeen young adults (24.11 ± 3.05 years) completed 4 bipedal standing attempts lasting 20 seconds each. Measurements were performed on AMTI plate and involved maintaining balance while standing barefoot on both feet with eyes open and closed. Two additional tests with provoked isometric voluntary muscle contraction were performed under the same visual conditions.

Results
For examined healthy subjects, the lack of visual feedback in combination with increased muscle tension caused a significant increase in the peak of sway in the anterior - posterior (AP) and medio - lateral (ML) direction. On the other hand, the values of the center of pressure (CoP) path length and its velocity due to the increased muscle contraction did not significantly decrease their values for trials with eyes open and closed.

Conclusions
This study indicates that voluntary muscle contraction can influence the standing posture mainly in combination with a lack of visual feedback, causing its deterioration.