Abstract des Autors

It is well documented that the microgravity environment encountered during spaceflight, or simulated by using models of weightlessness, induces structural and functional deficits in the musculoskeletal system, globally defined as deconditioning. It consists mainly of loss of the bone mass; increases in musculotendinous stiffness; and decreases in musculoarticular stiffness. Some countermeasures have been proposed in order to mitigate the deleterious effects of microgravity on the human muscle system and prolonged disuse. Most of the previous countermeasure programs have involved primarily aerobic leg exercise protocols using a cycle ergometer or treadmill, which have demonstrated the ability to attenuate alterations of aerobic fitness and help maintain cardiovascular function. However, significant losses in human isometric and isokinetic strength of upper and lower limbs have been reported in response to long-term spaceflight. Because cycle ergometers do not adequately exercise upper-body muscle groups, some apparatuses were conceived for upper-body muscles such as the “chest expanders” and “rope and pulley” devices. These apparatuses were not frequently used in most spaceflight missions because they induce unpleasant effects when applied at levels which require optimal physiological response. Indeed, exercising with these apparatuses at low resistances and high pulling rates induces rapid muscle fatigue which yields dynamic endurance rather than resistive muscular strength effects.