Effects Of Resistance Training During 8-week Bed-rest On Intramuscular-fat And Muscle-tissues Of The Thigh Muscle Groups

Abstract

We know that muscle tissue size is inversely associated with the amount of intramuscular fat (Akima et al. 2015). In prolonged bed-rest, atrophy of lower-limb muscle occurs, implying that an increase of intramuscular fat may occur in parallel. Successful countermeasures, such as resistance training, may also affect the amount of intramuscular fat. Given that muscles atrophy at different rates in disuse (Belavý et al. 2009), the adaptation in intramuscular adipose tissues may also muscle specific. PURPOSE: The purpose of this study was to quantify the effect of exercise during 8-week bed-rest on intramuscular fat and muscle tissue in individual thigh muscle groups. METHODS: Twenty-one men were randomized to either 8-week bed-rest with resistance exercise (TR-group, n = 13) or no exercise (CTR-group, n = 8). The training was performed 3 days a week and consisted of bilateral leg press, single and double leg heel raises, and back and forefoot raise. Axial images of the mid-thigh were taken before and after the bed-rest using magnetic resonance imaging. Intramuscular fat cross-sectional area (CSA) and muscle tissue CSA were measured in quadriceps femoris (QF), adductors (AD) and hamstrings (HM). We calculated the percent change of intramuscular fat CSA between before and after the bed-rest. RESULTS: After bed-rest, muscle tissue CSA in CTR was significantly decreased compared to before bed-rest in all muscle groups (p < 0.05), whereas muscle tissue CSA did not change in the TR-group. Intramuscular fat CSA in individual muscles did not change after bed-rest in either group (QF: CTR 7.3 ± 20.6 % vs. TR -38.0 ± 31.4 %, AD: CTR -3.8 ± 19.7% vs. TR -34.2 ± 26.1 %, HM: CTR -9.6 ± 26.8 % vs. TR -33.6 ± 30.1%). However, for intramuscular fat of all muscle groups pooled a significant difference between the groups was observed with a reduction of intramuscular fat in the TR group (CTR 1.0 ± 13.9 % vs. TR -36.2 ± 28.2 %, P=0.004). CONCLUSION: Resistance training during 8-week bed-rest reduces thigh muscle atrophy and results in a reduction in intramuscular fat. No evidence was seen on the impact of bed-rest itself, in inactive subjects, on intramuscular fat in the thigh muscle groups.