The intensity of the training stimulus and the effort exerted (regarded as an index of internal load) to complete an exercise session are driving forces for physiological processes and long-term training adaptations. This study compared the aerobic adaptations following two iso-effort, ratings of perceived exertion (RPE)-based training programs, an intense continuous (CON) and a high-intensity interval (INT). Young adults were assigned to a CON (n = 11) or an INT (n = 13) training group to perform 14 training sessions within 6 weeks. The INT group performed running bouts (9.3 ± 4.4 repetitions) at 90% of peak treadmill velocity (PTV) with bout duration equal to 1/4 of time to exhaustion at this speed (134.2 ± 27.9 s). The CONT group ran (1185.0 ± 487.6 s) at a speed corresponding to -2.5% of critical velocity (CV; 80.1% ± 3.0% of PTV). Training-sessions were executed until RPE attained 17 on the Borg scale. VO2max, PTV, CV, lactate threshold velocity (vLT), and running economy were assessed pre-, mid-, and post-training. Both CONT and INT methods increased (p < 0.05) VO2max (INT: 57.7 ± 8.1-61.41 ± 9.2; CONT: 58.1 ± 7.5-61.1 ± 6.3 mL kg-1 min-1), PTV (INT: 14.6 ± 1.8-15.7 ± 2.1; CONT: 15.0 ± 1.7-15.7 ± 1.8 km h-1), CV (INT: 11.8 ± 1.4-12.8 ± 1.8; CONT: 12.2 ± 1.6-12.9 ± 1.7 km h-1), and vLT (INT: 9.77 ± 1.1-10.8 ± 1.4; CONT: 10.4 ± 1.4-11.0 ± 1.8 km h-1) with no differences (p > 0.05) between them; running economy remained unchanged. The continuous training method, when matched for effort and executed at relatively high intensity at the upper boundaries of the heavy-intensity domain (∼80% of PTV), confers comparable aerobic adaptations to those attained after a high-intensity interval protocol following a short-term training period.
Keywords: HIIT; aerobic performance; continuous exercise; high intensity; interval training; iso-effort.