Attenuated Metabolic and Cardiorespiratory Responses to Isoenergetic High-Intensity Interval Exercise of Short Versus Long Bouts

Purpose To compare the metabolic, cardiorespiratory and perceptual responses to three isoenergetic high-intensity interval exercise (HIIE) protocols of different bout duration and an isoenergetic continuous exercise protocol. Methods Eleven healthy males (age, 28 +/- 6 yr) performed four 20-min cycling trials of equal mean power output 1 wk apart. Participants cycled either continuously (CON) or intermittently with 10 s (HIIE10), 30 s (HIIE30), or 60 s (HIIE60) bouts at intensities corresponding to 49% (CON) or 100% of power at peak oxygen uptake (V?O-2peak). Recovery intervals during the HIIE trials were 15, 45, and 90 s, respectively. Results Average V?O-2 was similar in the HIIE trials (2.29 +/- 0.42, 2.20 +/- 0.43, and 2.12 +/- 0.45 L center dot min(-1), for HIIE10, HIIE30, and HIIE60, respectively), whereas in CON (2.02 +/- 0.38 L center dot min(-1)), it was lower than HIIE10 (P = 0.002) and HIIE30 (P = 0.043). Average pulmonary ventilation (V-E) was higher in HIIE60 compared with HIIE10, HIIE30, and CON (75.8 +/- 21.8 L center dot min(-1) vs 64.1 +/- 14.5 L center dot min(-1), 64.1 +/- 16.2 L center dot min(-1), and 54.0 +/- 12.5 L center dot min(-1), respectively, P < 0.001). The peak values and oscillations of V?O-2 and V-E in HIIE60 were higher compared with all other trials (P < 0.001). Blood lactate concentration was higher in HIIE60 compared with HIIE10, HIIE30, and CON from the fifth minute onward, reaching 12.5 +/- 3.5, 7.2 +/- 2.1, 7.9 +/- 2.9, and 4.9 +/- 1.6 mmol center dot L-1, respectively, at the end of exercise (P < 0.001). RPE was higher and affective responses were lower in HIIE60 compared with all other trials toward the end of exercise (P < 0.001). Conclusions These findings highlight the importance of bout duration in HIIE, since shorter bouts resulted in attenuated metabolic and cardiorespiratory responses, lower RPE and feelings of displeasure compared with a longer bout, despite equal total work, duration, and work-to-recovery ratio. These results may have implications for the prescription of HIIE in various populations.

Automated summary

The study compared the effects of different high-intensity interval exercise (HIIE) protocols and an isoenergetic continuous exercise protocol on metabolic, cardiorespiratory, and perceptual responses. The results showed that bout duration in HIIE has a significant impact on metabolic, cardiorespiratory, and perceptual responses, as well as blood lactate concentration.