Effects of high-intensity resistance training on skeletal muscle and internal organs masses in humans

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Strength and power event athletes have an average of 20〜30 kg more fat-free mass (FFM) than non-athletes. Additionally, it has been reported that FFM increases by 1〜2 kg following 3〜4 months high-intensity resistance training. However, it is unknown whether the increase in FFM is attributed to the change in skeletal muscle mass only or in other organ-tissue masses. The purpose of the present study was to examine the relationship between resistance training-induced changes in FFM and changes in its major components of skeletal muscle, liver, kidneys and bone mass. Male college athletes performed two sessions/wk for six months of total body resistance training (five exercises, 70-80% of 1-RM, 4 sets). FFM was measured by two compartment densitometry. Contiguous magnetic resonance imaging was used to obtain images from the cervical vertebrae to the ankle joint for each subject. Skeletal muscle, liver and kidneys cross-sectional area and organ-tissue volumes were determined. Organ-tissue volume were converted to mass by multiplying the volume by the assumed constant density of the tissues. Bone mass was calculated from bone mineral mass using dual-energy X-ray absorptiometry. The changes in FFM and skeletal muscle mass were 1.2kg and 1.2kg, respectively. Resistance training-induced change in FFM was significantly correlated with that in skeletal muscle mass. Liver, kidneys and bone masses were not significantly different between before and after resistance training. These results suggest that the increase in FFM for a relatively short period of resistance training can be attributed to that in skeletal muscle mass.