Absence of respiratory muscle fatigue in high-intensity continuous or interval cycling exercise

Respiratory muscle fatigue (RMF) occurs during prolonged exercise (∼15-20 minutes) at >85% Vo 2 max. However, RMF has been reported to occur in ∼3-6 minutes in various modes of exercise at a high intensity. It is not known if continuous cycling exercise vs. repeated bouts of high-intensity interval training (HIT) at >85% Vo 2 max will lead to RMF. We hypothesized that RMF would occur after a constant load test and would be present before end exercise in an HIT protocol. Eight moderately active healthy men (21.7 ± 1.7 years; 181.3 ± 5.2 cm; 81.3 ± 2.3 kg) completed a Vo 2 max test on a cycle ergometer. Subjects then completed 2 bouts of HIT (7 × 1 minute, 2-minute recovery between intervals) and 3 bouts of continuous exercise (CE) tests at 90% of peak power (determined from an incremental exercise test to exhaustion). Maximal inspiratory pressure (P IMAX) and expiratory pressure (P EMAX) were measured pre- and post-exercise for both HIT and CE and after each interval during HIT. Decreases in postexercise P IMAX and P EMAX compared with baseline were used to determine RMF. There were no differences (p > 0.05) in P IMAX or P EMAX pre- to post-exercise for HIT (P IMAX pre: 134 ± 51, post: 135 ± 50 cmH 2 O; P EMAX pre: 143 ± 41, post: 148 ± 46 cmH 2 O) or CE (P IMAX pre: 135 ± 54, post: 133 ± 52 cmH 2 O; P EMAX pre: 146 ± 46, post: 148 ± 46 cmH 2 O) indicating RMF was not present following CE and HIT. These data suggest that repeated high-intensity cycling exercise at 90% peak power in a CE or HIT protocol does not lead to RMF.