The acute and chronic effects of exercise intensity and rest duration on physiological responses during 4-second sprint interval exercise
STUDY 1: Short sprint interval training (sSIT) is usually performed at maximal ‘all-out’ intensities, that are 5-8-times higher than the power needed to elicit VO2peak. However, the %VO2peak associated with repeated submaximal power sprints (%Pmax), particularly when paired with varying rest periods, remains unknown. The aim of this study was to systematically investigate the acute physiological responses induced by three levels of %Pmax intensities (50% and 75% of Pmax and all-out efforts) with three varying rest periods (15, 30, and 45-s) between thirty 4-s sprints. Eleven healthy, recreationally active participants took part in nine trials, performing thirty 4-s sprints during cycling with inertial loading at three different intensities and rest periods, in randomized order. Power outputs varied across differing intensities and rest periods. At 51% ± 0.7 and 75% ± 0.3 Pmax, the average output was constant within the rest periods. However, the ‘all-out’ efforts revealed that 15-s rest elicited a lower (p<0.001) %Pmax of 89% ± 0.8 compared to 98% ± 0.4, and 95% ± 0.4 of Pmax for 15 vs. 30, and 45-s of rest. VO2 varied with intensity (p<0.05) across all rest periods 48 ± 0.7%, 65 ± 1.1%, and 85 ± 1.2% of VO2peak for 15-second rest; 36 ± 0.5%, 45 ± 0.7%, and 66 ± 1.1% VO2peak for 30-second rest; and 28 ± 0.9%, 34 ± 0.8%, and 54 ± 2.2% VO2peak for 45-second rest, corresponding to intensities at 51%, 75%, and 89% of Pmax, respectively. A wide range of VO2 responses (i.e., 28-84% VO2peak) can systematically be elicited by varying the intensity and rest period during repeated 4-s sprints cycling using inertial loading, offering valuable insights for designing personalized training regimens. STUDY 2: All-out and maximal anaerobic power (Pmax) intensity are typically utilized in sprint interval training programs. However, limited research explores submaximal power sprints on cardiovascular and anaerobic power adaptations. This study aimed to investigate the chronic effects of training at 50% and 75% of Pmax, as well as all- out efforts, through 4-second Sprint Interval Training (SIT) over 8 weeks. The study involved 24 healthy, recreationally active participants (12 females, 12 males) who were randomly assigned to one of three training groups: ~50% Pmax, ~75% Pmax, or all-out (85% Pmax). Participants underwent an 8-week training program consisting of thirty bouts of 4- second SIT lasting 10 minutes, with sessions conducted three times per week. Peak oxygen consumption (VO2peak) and Pmax were measured before and after the training program. Significant improvements in VO2peak were observed in the ~75% Pmax group 2.79 ± 0.1 L/min to 3.13 ± 0.2 L/min (p < 0.05) and in the all-out group 2.93 ± 0.3 L/min to 3.30 ± 0.3 L/min (p < 0.001). Maximal anaerobic power also significantly increased, with the ~75% Pmax group from 876 ± 97 watts to 970 ± 100 watts (p < 0.05) and the all-out group from 1020 ± 139 watts to 1233 ± 149 watts (p < 0.001). However, the ~50% Pmax group did not significantly increase VO2peak or Pmax. In conclusion, this study demonstrates that 4-s short SIT at higher intensities (~75% of Pmax and all-out efforts), compared to 50% Pmax, leads to significant improvements in both VO2peak and maximal anaerobic power, while the 75% group experienced a reduced perceived rate of exertion compared to all-out group (p<0.05).
SIT, HIIT, Interval training, Cardiovascular health
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