Eight weeks of intermittent hypoxic training improves submaximal physiological variables in highly trained runners

Abstract: Holliss, BA, Burden, RJ, Jones, AM, and Pedlar, CR. Eight weeks of intermittent hypoxic training improves submaximal physiological variables in highly trained runners. J Strength Cond Res 28(8): 2195–2203, 2014—It is unclear whether intermittent hypoxic training (IHT) results in improvements in physiological variables associated with endurance running. Twelve highly trained runners (V[Combining Dot Above]O₂peak 70.0 ± 3.5 ml·kg^-1·min^-1) performed incremental treadmill tests to exhaustion in normobaric normoxia and hypoxia (16.0% F_IO₂) to assess submaximal and maximal physiological variables and the limit of tolerance (T-Lim). Participants then completed 8 weeks of moderate to heavy intensity normoxic training (control [CONT]) or IHT (twice weekly 40 minutes runs, in combination with habitual training), in a single blinded manner, before repeating the treadmill tests. Submaximal heart rate decreased significantly more after IHT (-5 ± 5 b·min^-1; p = 0.001) than after CONT ( -1 ± 5 b·min^-1; p = 0.021). Changes in submaximal V[Combining Dot Above]O₂ were significantly different between groups (p <= 0.05); decreasing in the IHT group in hypoxia (-2.6 ± 1.7 ml·kg^-1·min^-1; p = 0.001) and increasing in the CONT group in normoxia (+1.1 ± 2.1 ml·kg^-1·min^-1; p = 0.012). There were no V[Combining Dot Above]O₂peak changes within either group, and while T-Lim improved post-IHT in hypoxia (p = 0.031), there were no significant differences between groups. Intermittent hypoxic training resulted in a degree of enhanced cardiovascular fitness that was evident during submaximal, but not maximal intensity exercise. These results suggest that moderate to heavy intensity IHT provides a mean of improving the capacity for submaximal exercise and may be useful for pre-acclimatization for subsequent exercise in hypoxia, but additional research is required to establish its efficacy for athletic performance at sea level.