Article

It is widely accepted that Hoffmann (H) reflex amplitudes of the soleus decrease
as complexity of body positions increases, but it is not known if this same
mechanism of postural control is seen in other ankle muscles such as fibularis
longus (FL). Our purpose was to assess if FL H-reflex changed in different body
positions and if the adaptations were correlated to soleus H-reflex modulation.
Fifteen healthy subjects had their FL and soleus H-reflexes measured in three
positions (prone, bipedal, unipedal). Maximal H-reflexes
(H-max) and motor
responses (M-max) were collected bilaterally. The average H-max and M-max were
used to calculate H(max)/M(max) ratios. To control influences of background
muscle activity on H-reflex measures, the ratios were normalized to their
corresponding mean EMG amplitudes over a 50-ms time epoch. H-reflex amplitudes of
both muscles were significantly lower in unipedal stance than other positions.
Additionally, there were strong correlations (R(2)>0.7) in H-reflex modulation
between the two muscles when transitioning from prone to either bipedal or
unipedal stance. Down-modulation of H-reflex when transitioning to unipedal
stance was present in both FL and soleus suggesting that H-reflex modulation of
both muscles may play a similar role in control of upright posture.
CI - Copyright (c) 2012 Elsevier B.V. All rights reserved.

Langue : ANGLAIS