BACKGROUND: High-intensity interval training (HIIT) often utilizes a square-wave approach in which work rates (WR) immediately increase and decrease from work to rest intervals. An alternative to this is a ramped approach in which WR is constantly increasing, which may better reflect the supramaximal workloads associated with some sport or exercise modalities. This study examined physiological responses to a work-matched, ramped supramaximal HIIT protocol (RAMP) and a traditional, square-wave (SQR) HIIT protocol. METHODS: Nine healthy, college age males (23.9 ± 6.5 yrs.; 180.7 ± 8.2 cm; 84.5 ± 13.7 kg) completed a graded exercise test (20 W/min) on the cycle ergometer to exhaustion. Peak power output (PPO) was recorded to determine WR for the HIIT protocols. On separate days, participants performed the SQR protocol or the work-RAMP protocol in a randomized order. Protocols consisted of a warmup (20 W), followed by 5 work intervals (1:1-minute exercise/recovery ratio), and a cooldown (20 W). For CON, work rate increased at the start of each work interval to 80% PPO and remained constant while for RAMP, work rate continuously increased from 20 W to 160% PPO for each 1-minute work interval. Pulmonary oxygen uptake (VO2) and heart rate (HR) were measured continuously and averaged over the final 10 seconds of each interval (INT). Total oxygen cost (VO2tot) was calculated as the VO2 area under the curve from the start of the INT 1 to the end of INT 5. Two-way analysis of variance and post-hoc testing analyzed the mean difference between conditions at the end of warm-up (WU), and the end of INT 1, INT 3, and INT 5. Alpha level was set at p ≤ 0.05. RESULTS: Peak WR for SQR and RAMP were 207 ± 24 W and 414 ± 48 W, respectively. VO2 was significantly different between SQR and RAMP (p < 0.01 for all comparisons) at INT 3 (2.19 ± 0.28 vs. 2.49 ± 0.34 L/min) and INT 5 (2.39 ± 0.30 vs. 2.60 ± 0.31 L/min). HR was significantly different (p < 0.01 for all comparisons) between SQR and RAMP at all work intervals (INT 1: 131 ± 11 vs. 139 ± 14 bpm; INT 3: 147 ± 14 vs. 156 ± 15 bpm; INT 5: 155 ± 16 vs. 167 ± 16 bpm). VO2tot was not different between conditions (SQR: 1596.1 ± 163.2, RAMP: 1625.3 ± 162.0 L, p = 0.17). CONCLUSION: There is no significant difference VO2tot between two work-matched HIIT protocols, despite significant differences in oxygen consumption and heart rate at the end of work intervals.

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