EFFECTS OF ENDURANCE TRAINING ON OXIDATIVE CAPACITY AND STRUCTURAL COMPOSITION OF HUMAN ARM AND LEG MUSCLES

Six healthy subjects performed endurance training of the same duration with legs and arms consecutively. Performance and muscle structure we re measured before and after training in lower and upper limbs. Traini ng induced similar increases in maximal oxygen consumption (6 +/- 1 vs . 7 +/- 2 mL min(-1) kg(-1):legs vs. arms, P > 0.05) and mitochondrial volume in leg and arm muscles (42 +/- 12 vs. 31 +/- 11%. legs vs. arm s, P > 0.05). The gain in mitochondrial volume after training was achi eved solely by increasing the fraction of mitochondria (+40 +/- 11%, P < 0.05) in the same muscle volume (+2 +/- 2%, P > 0.05) in the legs. In contrast, increased muscle volume (+14 +/- 3%, P < 0.05), in additi on to a tendency for an increase in mitochondrial fraction (+16 +/- 11 %, P > 0.05), occurred in the arms after training. Thus, similar impro vements in muscle oxidative capacity in upper and lower limbs were bro ught about by different mechanisms. it is suggested that due to infreq uent use and a lack of load-bearing function, arm muscle volume is und erdeveloped in untrained, sedentary or detrained/injured subjects and that the mode of endurance training used in this study is sufficient t o enlarge arm muscle volume as well as aerobic capacity.