Citation

Baudry S, Duchateau J. J. Physiol. 2012; 590(Pt 21): 5541-5554.

Affiliation

Universite Libre de Bruxelles.

Copyright

(Copyright © 2012, The Physiological Society, Publisher John Wiley and Sons)

DOI

10.1113/jphysiol.2012.228932

PMID

22946095

Abstract

This study investigated the modulation of Ia afferent input in young and elderly adults during quiet upright stance in normal and modified visual and proprioceptive conditions. The surface electromyogram (EMG) of leg muscles, recruitment curve of the soleus (SOL) H reflex, and presynaptic inhibition of Ia afferents from SOL, assessed with the D1 inhibition and single motor unit methods, were recorded when young and elderly adults stood with eyes open or closed on two surfaces (rigid vs. foam) placed over a force platform. The results showed that elderly adults had a longer path length for the centre of pressure and larger antero-posterior body sway across balance conditions (P<0.05). Muscle EMG activities were greater in elderly compared with young adults (P<0.05), whereas the Hmax/Mmax ratio was lower (P = 0.048) in elderly (38 ± 16%) than young adults (58 ± 16%). The conditioned H/test H reflex (D1 inhibition method) increased with eye closure and when standing on foam (P<0.05), with greater increases for elderly adults (P = 0.019). These changes were accompanied by a reduced peak motor unit discharge probability when standing on rigid and foam surfaces (P ≤ 0.001), with a greater effect for elderly adults (P = 0.026). Based on these latter results, the increased conditioned H/test H ratio in similar sensory conditions likely reflects occlusion at the level of presynaptic inhibitory interneurones. Together, these findings indicate that elderly adults exhibited greater modulation of Ia presynaptic inhibition than young adults with variation in the sensory conditions during upright standing.

Language: en