Physiological Responses to Treadmill Running With Body Weight Support in Hypoxia Compared With Normoxia

CONTEXT: Anecdotal reports suggest elite sports clubs combine lower-body positive-pressure rehabilitation with a hypoxic stimulus to maintain or increase physiological and metabolic strain, which are reduced during lower-body positive pressure. However, the effects of hypoxia on cardiovascular and metabolic response during lower-body positive-pressure rehabilitation are unknown.

OBJECTIVE: Evaluate the use of normobaric hypoxia as a means to increase physiological strain during body-weight-supported (BWS) running.

DESIGN: Crossover study.

SETTING: Controlled laboratory.

PARTICIPANTS: Seven familiarized males (mean (SD): age, 20 (1) y; height, 1.77 (0.05) m; mass, 69.4 (5.1) kg; hemoglobin, 15.2 (0.8) g·dL-1) completed a normoxic and hypoxic (fraction of inspired oxygen [O2] = 0.14) trial, during which they ran at 8 km·h-1 on an AlterG™ treadmill with 0%, 30%, and 60% BWS in a randomized order for 10 minutes interspersed with 5 minutes of recovery.

MAIN OUTCOME MEASURES: Arterial O2 saturation, heart rate, O2 delivery, and measurements of metabolic strain via indirect calorimetry.

RESULTS: Hypoxic exercise reduced hemoglobin O2 saturation and elevated heart rate at each level of BWS compared with normoxia. However, the reduction in hemoglobin O2 saturation was attenuated at 60% BWS compared with 0% and 30%, and consequently, O2 delivery was better maintained at 60% BWS.

CONCLUSION: Hypoxia is a practically useful means of increasing physiological strain during BWS rehabilitation. In light of the maintenance of hemoglobin O2 saturation and O2 delivery at increasing levels of BWS, fixed hemoglobin saturations rather than a fixed altitude are recommended to maintain an aerobic stimulus.