A Countermeasure for Preventing Atrophy of Musculoskeletal System under Microgravity

Weightless environments such as bed rest and spaceflight are associated with dramatic losses of muscle volume and bone mass that hinder patients' or astronauts' health and reintegration into daily life. We developed a novel "hybrid exercise" (HYB) as a countermeasure to prevent the losses by using electrically stimulated muscles to provide resistance to the voluntary motion of a muscle undergoing training. Unilateral lower leg suspension (ULLS) of four weeks was carried out for young males as a simulation model of the weightless environment. The HYB for healthy men increased muscle strength and bulk in flexor and extensor around the knee joint. These effects were confirmed in the ULLS group as well as in the case of healthy subjects. The HYB showed good effects on the femurs of the ULLS group, especially on the greater trochanter. Some parameters of electrical stimulation and noise reduction methods were examined for moderating stimulation and for evaluating the effect, respectively.