Proceedings of The Physiological Society
University College London December 2005 (2006) Proc Physiol Soc 1, C4
Modulation of the H-reflex within naturally occurring sway during quiet standing
Tokuno, Craig D; Cresswell, Andrew G;
1. Human Movement Studies and Health and Rehabilitation Sciences, The University of Queensland, Brisbane, QLD, Australia. 2. Neuroscience, Karolinska Institutet, Stockholm, Sweden. 3. Idrottshogskolan, Stockholm, Sweden.
Previous research has observed a decrease in reflex excitability as subjects move from lying or sitting to a standing position. This decrease is thought to be due to increased presynaptic inhibition at the Ia synapse (Katz et al. 1988; Koceja et al. 1993). It is not known whether these same reflexes are modulated in a similar fashion within naturally occurring postural sway during quiet standing. H-reflex and M-wave recruitment curves were obtained in the right soleus (SOL) and medial gastrocnemius (MG) muscles while human subjects (n=7) were in a standing position. Electrical stimuli (1 ms duration pulse between 0.5 to 14 mA) were delivered to the tibial nerve when the body was naturally swaying forward (centre of pressure (COP) at 1.6 standard deviations (SD) anterior to the mean baseline COP) or backward (COP at 1.6 SD posterior to the mean baseline COP). The two sway conditions were characterized by a difference of 0.5 deg, 1.1 cm, and 0.8 cm in the mean ankle angle, position of the centre of pressure, and position of the centre of mass, respectively. Compared to when swaying backward, forward sway resulted in a significant increase in Hmax for the SOL and MG muscles by 11.2
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