High-intensity flywheel exercise and recovery of atrophy after 90 days bed--rest

Abstract

Aims: To investigate differential muscle atrophy during bed-rest, the impact of a high-intensity concentric-eccentric (flywheel) resistance exercise countermeasure and muscle recovery after bed-rest.

Methods: Twenty-five healthy male subjects underwent 90 dayshead-down tilt bed-rest. Volume of individual lower-limb muscles was measured via MRI before, twice during and four times up to 1 year after bed-rest. Subjects were either inactive (n=16) or performed flywheel exercise every third day of bed-rest (n=9). Functional performance was assessed via countermovement jump.

Results: On 'intent-to-treat' analysis, flywheel prevented atrophy in the vasti (p<0.001) and reduced atrophy in the hip adductor/extensor adductor magnus (p=0.001) and ankle dorsiflexors/toe flexors (soleus (p<0.001), gastrocnemius medialis (p<0.001), gastrocnemius lateralis (p=0.02), and tibialis posterior with flexor digitorum longus (p=0.04)). Flywheel exercise was not effective for the hamstrings, gracilis, sartorius, peroneals and anterior tibial muscles. Muscle atrophy in vasti, soleus, gastrocnemius medialis, gastrocnemius lateralis and adductor magnus correlated with losses in countermovement jump performance. Muscle volume recovered within 90 days after bed-rest, however long-term after bed-rest, the inactive subjects only showed significantly increased muscle volume versus prebed-rest in a number of muscles including soleus (+4.3%), gastrocnemius medialis (+3.9%) and semimembranosus (+4.3%). This was not associated with greater countermovement jump performance.

Conclusion: The exercise countermeasure was effective in preventing or reducing atrophy in the vasti, adductor magnus and ankle dorsiflexors/toe flexors but not the hamstrings, medial thigh muscles or peroneals and dorsiflexor muscles.

Trial registration number: NCT00311571; results.

Keywords: Exercise; Exercise rehabilitation; Muscle.

Figure 1

Atrophy and impact of exercise on muscle atrophy values are mean (SD) time constants (‘k’) of exponential decay of muscle volume per week of bed-rest. *: p<0.05; †:p<0.01; ‡: p<0.001 and indicate significance of difference of time constant to zero (ie, whether atrophy occurred). p Values above the columns show where the difference between groups was significant. All p values are adjusted for false positives via the ‘false discovery rate’ method.

Figure 2

Increases muscle volume 1 year after bed-rest in inactive subjects only: muscle volume change at end bed-rest versus muscle volume 1 year after bed-rest. Values are mean percentage difference to baseline at end of bed-rest (x-axis) versus 360 days after bed-rest (y-axis). For the inactive group only, the error bars indicate the unadjusted 95% CI of the mean percentage change 360 days after bed-rest. The muscles where the unadjusted 95% CI 360 days after bed-rest does not cross zero are labelled. Note that the effect (A) was isolated to the inactive group and (B) did not appear to be related to the extent of muscle loss during bed-rest.