Jj. Eng et Ja. Hoffer, REGIONAL VARIABILITY OF STRETCH REFLEX AMPLITUDE IN THE CAT MEDIAL GASTROCNEMIUS-MUSCLE DURING A POSTURAL TASK, Journal of neurophysiology, 78(2), 1997, pp. 1150-1154
The relationship between local fibre stretch velocity (mechanical inpu
t) and the corresponding local reflex electromyographic (EMG) amplitud
e (a measure of the neural output) was assessed to determine the contr
ibution of muscle spindle feedback in postural control. We hypothesize
d that traditionally measured input variables (e.g., the velocity of a
n external movement or whole muscle velocity) may not accurately repre
sent the mechanical input to the muscle spindles, especially when the
background forces are small. Three cats were trained to stand on pedes
tals while ankle rotations were applied to the left hindlimb. EMG and
fiber movement in both proximal and distal regions of the muscle were
recorded in addition to muscle length and tendon force. We found that
local muscle velocity was correlated poorly with whole muscle velocity
, demonstrating that internal and external muscle movements are often
dissimilar, particularly during tasks that involve modest levels of mu
scle activation. Local EMC reflex amplitudes were correlated well with
the corresponding local fiber stretch velocities (R values ranging fr
om 0.5 to 0.8) but not with muscle stretch velocity. The lack of cross
ed correlations between fiber stretch velocities and reflex EMG amplit
udes measured in proximal versus distal regions of the muscle suggests
the presence of a local reflex component. It is concluded that change
s in local muscle fiber length represent the mechanical input to spind
les better than changes in the total muscle length. Additionally, spin
dles have a specific role in the reflex activation of nearby muscle fi
bers.