Intermittent hypoxic resistance training: does it provide added benefit?

Methods to enhance the adaptive responses to resistance training are of great interest to clinical and athletic populations alike. Altering the muscular environment by restricting oxygen availability during resistance exercise has been shown to induce favorable physiological adaptations. An acute hypoxic stimulus during exercise essentially increases reliance on anaerobic pathways, augmenting metabolic stress responses, and subsequent hypertrophic processes (Scott et al., 2014). Hypoxic strategies during resistance exercise were originally investigated using blood flow restriction (BFR) methods (Takarada et al., 2000), whereby a cuff is applied proximally to a limb to partially limit arterial inflow while occluding venous outflow from the working muscles. Another method that has been investigated more recently is performing resistance exercise in systemic hypoxia, by means of participants breathing a hypoxic air mixture. The addition of systemic hypoxia to resistance training has previously resulted in significantly enhanced hypertrophic and strength responses to both low-load (20% 1-repetition maximum; 1RM) (Manimmanakorn et al., 2013a,b) and moderate-load (70% 1RM) (Nishimura et al., 2010) resistance training. While research into intermittent hypoxic resistance training (IHRT) is in its infancy, some studies have reported conflicting results, which is likely due to differing research methodologies. In a recent review, it has been suggested that many of the potential mechanisms underpinning muscle adaptations to BFR training and IHRT are linked to the muscular oxygenation status and degree of metabolic stress associated with exercise (Scott et al., 2014). The purpose of this paper is to briefly summarize the adaptive responses that have been reported following both low- and moderate-load IHRT and to highlight key areas of concern for IHRT methodology, including the level of hypoxia used and the degree of metabolic stress imposed during exercise.