Practical and effective exercises on human musculoskeletal systems in weightless environments

Weightless environments such as bedrest and spaceflight are associated with profound losses of muscle bulk and strength which hinder patient's or astronaut's health and reintegration into daily life. To prevent the losses, we developed a practical and effective training method with electrical stimulation, named "hybrid exercise"; electrical stimulations are added to antagonists at joints in order to produce resistance forces in one' s own body. The environment was simulated to evaluate the effects of the hybrid exercise on human body. An unilateral lower limb suspension (ULLS) was introduced as a simulation model of the weightless environment. Two kinds of experiments have been done: (1, ULLS experiment) only ULLS was executed to make disuse of lower limb.: (2, ULLS-Hybrid experiment) ULLS combined with the hybrid exercise to prevent losses of lower limb functions. We evaluated experiments by four items, maximum volitional contraction (MVC), cross-sectional area (CSA), bone mineral density (BMD), and electromyogram (EMG). The ULLS experiment showed dramatic losses of these parameters, whereas the ULLS-Hybrid experiment showed good effects of the hybrid exercise to prevent the losses.