Running mechanics adjustments to perceptually-regulated interval runs in hypoxia and normoxia

We determined whether perceptually-regulated, high-intensity intermittent runs in hypoxia and normoxia induce similar running mechanics adjustments within and between intervals.

Within-participants repeated measures.

Nineteen trained runners completed a high-intensity intermittent running protocol (4×4-min intervals at a perceived rating exertion of 16 on the 6-20 Borg scale, 3-min passive recoveries) in either hypoxic (FiO₂=0.15) or normoxic (FiO₂=0.21) conditions. Running mechanics were collected over 10 consecutive steps, at constant velocity (∼15.0±2.0km.h^-1), at the beginning and the end of each 4-min interval. Repeated measure ANOVA were used to assess within intervals (onset vs. end of each interval), between intervals (interval 1, 2, 3 vs. 4) and FiO₂ (0.15 vs. 0.21) main effects and any potential interaction.

Participants progressively reduced running velocity from interval 1-4, and more so in hypoxia compared to normoxia for intervals 2, 3 and 4 (P<0.01). There were no between intervals (across all intervals P>0.298) and FiO₂ (across all intervals P>0.082) main effects or any significant between intervals×within intervals×FiO₂ interactions (all P>0.098) for any running mechanics variables. Irrespective of interval number or FiO₂, peak loading rate (+10.6±7.7%; P<0.001) and duration of push-off phase (+2.0±3.1%; P=0.001) increased from the onset to the end of 4-min intervals, whereas peak push-off force decreased (-4.0±4.0%; P<0.001).

When carrying out perceptually-regulated interval treadmill runs, runners adjust to progressively slower velocities in hypoxia compared to normoxia. However, only subtle constant-velocity modifications of their mechanical behaviour occurred within each set, independently of FiO₂ or interval number.