[Effects of gravitational unloading on blood supply of working muscles]

Exposure to the conditions of simulated gravitational unloading (head down tilting, dry immersion) produces a material effect on blood supply of working muscles in humans that may depend on type of work (local or global) and posture (vertical or horizontal). Peak blood flow in the calf after exposure to HDT and dry immersion reduces by 7 to 20% and the post-contraction hyperemia (PCH) following a standard work of the calf extensors noticeably increases. In contrast to PCH, blood flow during natural locomotion diminishes as a result of simulated gravitational unloading. Standard bicycling by sitting and supine human subjects moderates and exaggerates the post-work hyperemia, respectively. Consideration is given to possible causes of these effects.