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

Abstract

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.

Keywords: altitude; lower body positive pressure; rehabilitation.