Introduction: Atrophy of the leg muscles is a serious consequence of disuse and occurs with prolonged exposure to microgravity. We investigated whether intense interval training on a cycle ergometer would prevent muscle changes during unilateral lower limb suspension (ULLS).
Methods: This study involved 11 healthy men who were divided into 2 groups, one with training on a cycle ergometer (TRN, N=6) and the other a control group (CON, N=5). TRN performed intense interval training (up to 90% of maximum heart rate) on alternate days during 20 d of unloading. Maximum voluntary contraction (MVC) of the quadriceps femoris and volume of the thigh muscle were measured before and after unloading. Muscle functional magnetic resonance imaging (mfMRI), which reflects the contractile activity of the activating muscle, were acquired during submaximal dynamic knee extension exercises.
Results: The MVC was significantly decreased in TRN (-11.1%) and CON (-18.7%). The total volume of the thigh muscles was maintained in TRN (-0.2%); however, a significant decrease was found in CON (-6.9%). The mfMRI signal increase for submaximal exercise did not change for TRN; however, it significantly increased for CON.
Conclusions: Although the power of this study was limited, these results suggest that training on a cycle ergometer counteracts some of the effects of unloading and merits further study as a potential countermeasure for muscle changes in microgravity.