Lower-limb muscle atrophy and effect of resistive vibration exercise during 56-day bed-rest

Abstract

Objectives:
Developing more efficient countermeasures for the maintenance of muscle and muscle function in spaceflight is a priority for space agencies. In this work, we examine changes in muscle volume of the lower-limb during prolonged bed-rest and the impact of a high-intensity resistive vibration exercise (RVE) countermeasure as part of the 1st Berlin Bed-Rest Study (2003 and 2004).

Methods:
20 male subjects underwent 56-days of bed- and were assigned to either an inactive control, or a countermeasure group which performed high-load resistive exercises with whole-body vibration. 11 exercise sessions were performed per week, with exercises including including squats, heel raises, toe raises and ‘kicks’ against a vibrating platform. Magnetic resonance imaging of the lower-limbs was performed at two-weekly intervals and the volumes of individual muscles were measured.

Results:
In the control group, rate of muscle atrophy differed between muscles (F=8.81, p3.0, p<.025) in the triceps surae (-6.6 [1.8]% vs. -18.3 [2.0]%) and the vastii (-4.6[1.6]% vs. -15.9[3.7]%) muscles, but did not impact upon atrophy of the hamstring muscles (-10.9[2.2]% vs. -11.3[3.1]%). Conclusions: Understanding which muscles are most affected by bed-rest helps to design more time efficient training programmes to target these particular muscle groups. The limited effect of RVE on the hamstrings was possibly due to insufficient hip flexion/extension during squat exercises. Consideration of the results of the current and other works suggests that (resistive) exercise needs to be performed at high-loads to maintain muscle mass during prolonged bed-rest.