Is hypoxia a stimulus for synthesis of oxidative enzymes and myoglobin?

Abstract

To compare two situations with similar magnitudes of mitochondrial substrate flux but different blood oxygen contents, one-legged training was employed. Ten healthy subjects trained one leg under normobaric conditions and the other under hypobaric conditions. At each session the subjects trained each leg for 30 min. The absolute work intensity was the same for both legs and was chosen to correspond to 65% of the average (right and left) pretraining one-legged maximal work capacity. There were three to four training sessions per week for 4 wk. Muscle biopsies from each leg were taken before and after training and analyzed for fiber types, capillaries, myoglobin, and oxidative and glycolytic enzymes. The most striking finding was a greater increase of citrate synthase activity under hypobaric conditions than under normobaric conditions. In addition, the myoglobin content increased in the leg trained under hypobaric conditions, whereas it tended to decrease in the normobarically trained leg. Because both legs were trained at the same intensity, the oxygen turnover and the substrate flux through the carboxylic acid cycle and the respiratory chain must have been of similar magnitude. Thus a difference in substrate flux is less likely to have caused the differences in enzyme activities and myoglobin content between training under normobaric and hypobaric conditions. Instead, the stimulus seems to be related to the blood oxygen content or tension.

Estimated contribution of hemoglobin and myoglobin to near infrared spectroscopy

“…Similar capillary densities have been measured in human skeletal muscle [e.g., 286 cap/mm 2 (Celsing, 1988), 300-550 cap/mm 2 (Terrados, 1986, Terrados, 1990]. A higher capillary density has the potential to increase the LAP of Hb in skeletal muscle.…”

“…A higher [Mb] has the potential to accommodate the increased DO 2 needs in Type I fibers which are highly oxidative and tend to have a higher capillary and mitochondrial density. Terrados et al (1986Terrados et al ( , 1990 (Warriss, 1979, Reynafarje, 1963, Terrados et al, 1990, Celsing et al, 1988, Terrados et al, 1986. Van Beek-Harmsen et al (2004) To correct for the reduced capillary hematocrit at rest relative to systemic hematocrit the value of 0.5 was used, derived from direct observations of the resting capillary Hct of ~22% and systemic Hct of ~45% (Kindig and Poole, 2001, Russell et al, 2003, Kindig and Poole, 1998.…”

Implications of moderate altitude training for sea-level endurance in elite distance runners

“…Some adaptations may facilitate endurance performance, whereas others are less bene®cial. Although equivocal, human studies have demonstrated that either hypobaric or normobaric hypoxia per se is responsible for increases in blood haemoglobin (Hb) concentration (Berglund 1992), muscle mitochondrial volume, capillary supply (Desplanches et al 1993), aerobic enzyme activities and myoglobin concentration (Terrados et al 1990), 2,3-diphosphoglycerate (Mairbaurl et al 1986), rate of free fatty acid mobilisation (Young et al 1982) or an elevated blood bu ering capacity (Favier et al 1995). Altitude acclimatisation improves physical performance at altitude (Pugh 1967;Maher et al 1974), but the e ects on sea-level performance are less clear.…”

Hypoxia reprograms calcium signaling and regulates myoglobin expression

“…Studies that evaluated the interaction between hypoxia and myoglobin have yielded conflicting results (14,26,43). As outlined previously, selected animal and human studies suggest that myoglobin expression is induced in response to hypoxia.…”