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The effects of training in hyperoxia vs. normoxia on skeletal muscle enzyme activities and exercise performance

¹Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario; and ²Department of Medicine, McMaster University, Hamilton, Ontario, Canada

Submitted 26 October 2006 ; accepted in final form 5 December 2006

Inspiring a hyperoxic (H) gas permits subjects to exercise at higher power outputs while training, but there is controversy as to whether this improves skeletal muscle oxidative capacity, maximal O₂ consumption (O_{2 max}), and endurance performance to a greater extent than training in normoxia (N). To determine whether the higher power output during H training leads to a greater increase in these parameters, nine recreationally active subjects were randomly assigned in a single-blind fashion to train in H (60% O₂) or N for 6 wk (3 sessions/wk of 10 x 4 min at 90% O_{2 max}). Training heart rate (HR) was maintained during the study by increasing power output. After at least 6 wk of detraining, a second 6-wk training protocol was completed with the other breathing condition. O_{2 max} and cycle time to exhaustion at 90% of pretraining O_{2 max} were tested in room air pre- and posttraining. Muscle biopsies were sampled pre- and posttraining for citrate synthase (CS), -hydroxyacyl-coenzyme A dehydrogenase (-HAD), and mitochondrial aspartate aminotransferase (m-AsAT) activity measurements. Training power outputs were 8% higher (17 W) in H vs. N. However, both conditions produced similar improvements in O_{2 max} (11–12%); time to exhaustion (100%); and CS (H, 30%; N, 32%), -HAD (H, 23%; N, 21%), and m-AsAT (H, 21%; N, 26%) activities. We conclude that the additional training stimulus provided by training in H was not sufficient to produce greater increases in the aerobic capacity of skeletal muscle and whole body O_{2 max} and exercise performance compared with training in N.

citrate synthase; -hydroxyacyl-coenzyme A dehydrogenase; mitochondrial oxidative capacity; high-intensity interval training