Joint Stiffness Fluctuations are Potentially Associated with Postural Sway

Abstract

Joint stiffness can be induced by simultaneous contraction of muscles on opposite sides of the joint. When the electrical oscillations of these antagonistic muscles are in-phase, fluctuations in joint stiffness can occur, which can pose a threat to those with a neuromuscular deficit, as they will not be able to adequately control these fluctuations. In an attempt to develop rehabilitation programs to train these individuals on how to control these fluctuations, electrical activity of the muscles in the lower leg, and postural sway were measured. It was hypothesized that the amplitude coherence of low-frequency, in-phase oscillations of antagonistic muscles was positively correlated with postural sway. Data collection occurred while subjects were standing in the tandem stance, a position of induced coactivation of the antagonistic muscles of the lower leg. Electrical activity of the right tibialis anterior, medial gastrocnemius, and soleus were measured and analyzed against center-of-pressure power, a measure of postural sway. EMG measurements, such as amplitude coherence and power spectral density, were only analyzed at low-frequencies (0-3 Hz) at which the oscillations were in-phase. Data analysis yielded no significant correlations between amplitude coherence and center-of-pressure power, and no significant correlations between power spectral density and center-of-pressure power. Future modifications to this study can incorporate visual feedback in order for subjects to be able to modulate their muscle activity to hit a specific target of co-activation, and COP sway will be measured simultaneously.