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Control of the triceps surae during the postural sway of quiet standing
Author(s) -
Tokuno C. D.,
Carpenter M. G.,
Thorstensson A.,
Garland S. J.,
Cresswell A. G.
Publication year - 2007
Publication title -
acta physiologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.591
H-Index - 116
eISSN - 1748-1716
pISSN - 1748-1708
DOI - 10.1111/j.1748-1716.2007.01727.x
Subject(s) - triceps surae muscle , center of pressure (fluid mechanics) , physical medicine and rehabilitation , h reflex , medicine , electromyography , quiet , force platform , anatomy , physical therapy , physics , mechanics , aerodynamics , quantum mechanics
Aim: The present study investigated how the triceps surae are controlled at the spinal level during the naturally occurring postural sway of quiet standing. Methods: Subjects stood on a force platform as electrical stimuli were applied to the posterior tibial nerve when the center of pressure (COP) was either 1.6 standard deviations anterior (COP ant ) or posterior (COP post ) to the mean baseline COP signal. Peak‐to‐peak amplitudes of the H‐reflex and M‐wave from the soleus (SOL) and medial gastrocnemius (MG) muscles were recorded to assess the efficacy of the Ia pathway. Results: A significant increase in the H max : M max ratio for both the SOL (12 ± 6%) and MG (23 ± 6%) was observed during the COP ant as compared to the COP post condition. The source of the modulation between COP conditions cannot be determined from this study. However, the observed changes in the synaptic efficacy of the Ia pathway are unlikely to be simply a result of an altered level of background electromyographic activity in the triceps surae. This was indicated by the lack of differences observed in the H max : M max ratio when subjects stood without postural sway (via the use of a tilt table) at two levels of background activity. Conclusions: It is suggested that the phase‐dependent modulation of the triceps surae H‐reflexes during the postural sway of quiet standing functions to maintain upright stance and may explain the results from previous studies, which, until now, had not taken the influence of postural sway on the H‐reflex into consideration.