20-Hz whole body vibration training fails to counteract the decrease in leg muscle volume caused by 14 days of 6 degrees head down tilt bed rest

A 6 degrees head down tilt bed rest (HDT) was used to simulate the effects of muscle unloading in space. We tested whether vibration training (VT) reduces the decrease in leg muscle volume induced by 14 days HDT. In two study phases eight healthy male subjects received both (1) HDT and VT or (2) HDT and a control intervention. Twice daily five intervals of 1 min VT were performed (20 Hz, 2-4 mm) in upright standing position followed by 1 min breaks in seated position. The control intervention included identical procedures except the vibration plate was off. Before and the day after HDT volumes of upper and lower leg muscles were measured using magnetic resonance imaging. HDT combined with control intervention caused a significant (P < 0.05) decrease in the volumes of muscles by -4 to -6.5%. VT failed to counteract the decrease in leg muscle volume induced by HDT.