Endurance training under 2500-m hypoxia does not increase myoglobin content in human skeletal muscle

The present study was carried out to determine whether myoglobin (Mb) conce ntration ([Mb]) in human skeletal muscle is influenced by 8 weeks of endura nce training under normal conditions, and under hypoxic conditions equivale nt to an altitude of 2500 m. Fourteen healthy but sedentary male adults who did not participate in any regular exercise program took part in this stud y. They were divided into two groups according to the training regime to wh ich they were submitted: the N group, who exercised under normobaric condit ions, and the H group, who exercised under hypobaric conditions. All subjec ts performed an incremental cycling exercise at sea level to evaluate their maximal O-2 uptake ((V)over dotO(2max)) before and after the 8-week endura nce training course period. Muscle tissue samples were obtained by needle b iopsy from the vastus lateralis muscle for histochemical and biochemical an alysis. Training induced an increase in (V)over dotO(2max) in both the N an d H groups (P < 0.05), although there was no significant difference in thes e changes between groups. The 8-week training had no effect on [Mb] in eith er group. Muscle fiber composition was also unaffected by the training cour se. In contrast, citrate synthase activity in both groups increased by [mea n (SD)] 28.2 (33.3)% (N: P < 0.01) and 32.0 (18.2)% (H: P < 0.05) after tra ining, and the number of capillaries (capillary: fiber ratio) increased by 47.7 (33.8)% (N: P < 0.01) and 32.3 (20.6)% (H: P < 0.05). There were no si gnificant differences in these parameters between the N and H groups. These results suggest that significant improvement of aerobic potential as a res ult of endurance training are not accompanied by increases in [Mb] in human skeletal muscle. In addition, a lower absolute workload may not be suffici ent to stimulate Mb synthesis in humans, even where endurance training is c arried out under hypoxia.