The relationship between dynamic balancing ability and posture related modulation of the soleus H reflex.
Soleus H reflex reveals down modulation with increased postural difficulty. Role of this posture related reflex modulation is thought to shift movement control toward higher motor centers in order to facilitate more precise postural control. Present study hypothesized that the ability to modulate H reflex is related to one's ability to dynamically balance while in an unstable posture. This study examined the relationship between dynamic balancing ability and soleus H reflex posture related modulation. Thirty healthy adults participated. The soleus maximal H reflex (Hmax) motor response (Mmax) and background EMG activity (bEMG) were obtained during three postural conditions: prone, open legged standing, and closed legged standing. Hmax/Mmax ratios were normalized via the corresponding bEMG in order to remove the effects of background muscle activity from the obtained H reflex. Reflex modulation was calculated as the ratio of the normalized Hmax/Mmax ratios in one postural condition to another posture in a more difficult condition. Dynamic balancing ability was assessed by testing stability while standing on a wobble board. A significant negative correlation was observed between balancing scores and reflex modulation from open legged standing to closed legged standing. This suggests that the ability to modulate monosynaptic stretch reflex excitability in response to a changing posture is a significant factor for dynamic balancing.
Journal of electromyography and kinesiology official journal of the International Society of Electrophysiological Kinesiology