Effects of long-term spaceflight on mechanical properties of muscles in humans.
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.
Lambertz
D
D
Département de Génie Biologique, CNRS UMR-6600, Université de Technologie, F-60205 Compiègne cedex, France.
Pérot
C
C
Kaspranski
R
R
Goubel
F
F
D018480:Astronauts; D001696:Biomechanical Phenomena; D004548:Elasticity; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D007596:Joints / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D013026:Space Flight; D013710:Tendons / Q000502:physiology