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1 Département de Génie Biologique, CNRS UMR-6600, Université de Technologie, F-60205 Compiègne cedex, France; and 2 Y. A. Gagarin Cosmonauts Training Centre, Star City, 141160 Moscow Region, Russia
The effects of long-term spaceflight
(90-180 days) on the contractile and elastic characteristics of
the human plantarflexor muscles were studied in 14 cosmonauts before
and 2-3 days after landing. Despite countermeasures practiced
aboard, spaceflight was found to induce a decrease in maximal isometric
torque (17%), whereas an index of maximal shortening velocity was
found to increase (31%). In addition, maximal muscle activation
evaluated during isokinetic tests decreased by 39%. Changes in
musculotendinous stiffness and whole joint stiffness were characterized
by means of quick-release movements and sinusoidal perturbations.
Musculotendinous stiffness was found to be increased by 25%. Whole
joint stiffness decreased under passive conditions (21%), whereas
whole joint stiffness under active conditions remained unchanged after
spaceflight (
1%). This invariance suggests an adaptive mechanism to
counterbalance the decrease in stiffness of passive structures by an
increased active stiffness. Changes in neural drive could participate
in this equilibrium.
isometric force; isokinetic contraction; musculotendinous stiffness; musculoarticular stiffness
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