Differential atrophy of the postero-lateral hip musculature during prolonged bedrest and the influence of exercise countermeasures

As part of the 2nd Berlin BedRest Study (BBR2-2), we investigated the pattern of muscle atrophy of the postero-lateral hip and hamstring musculature during prolonged inactivity and the effectiveness of two exercise countermeasures. Twenty-four male subjects underwent 60 days of head-down tilt bedrest and were assigned to an inactive control (CTR), resistive vibration exercise (RVE), or resistive exercise alone (RE) group. Magnetic resonance imaging (MRI) of the hip and thigh was taken before, during, and at end of bedrest. Volume of posterolateral hip and hamstring musculature was calculated, and the rate of muscle atrophy and the effect of countermeasure exercises were examined. After 60 days of bedrest, the CTR group showed differential rates of muscle volume loss (F = 21.44; P ≤ 0.0001) with fastest losses seen in the semi-membranosus, quadratus femoris and biceps femoris long head followed by the gluteal and remaining hamstring musculature. Whole body vibration did not appear to have an additional effect above resistive exercise in preserving muscle volume. RE and RVE prevented and/or reduced muscle atrophy of the gluteal, semi-membranosus, and biceps femoris long head muscles. Some muscle volumes in the countermeasure groups displayed faster recovery times than the CTR group. Differential atrophy occurred in the postero-lateral hip musculature following a prolonged period of unloading. Short-duration high-load resistive exercise during bedrest reduced muscle atrophy in the mono-articular hip extensors and selected hamstring muscles. Future countermeasure design should consider including isolated resistive hamstring curls to target this muscle group and reduce the potential for development of muscle imbalances.