Acute Responses to SIT, BIT, and SIT-BIT

Purpose: Sprint Interval Training (SIT) and Burpee Interval Training (BIT) are time-efficient strategies that elicit distinct physiological and psychological responses. However, the acute effects of combining both approaches within a single low-volume session remain unclear. Method(s): Fourteen recreationally active adults (9 men, 5 women; 25.6 ± 5.5 yr; maximum oxygen consumption [V̇O₂max]: 45.5 ± 8.3 ml·kg⁻¹·min⁻¹) completed three randomized, within-subject sessions comparing low-volume SIT, BIT, and a combined SIT-BIT protocol. Each session consisted of 10 × 5-s all-out efforts: 35-s passive recovery (≈6 min). Heart rate (HR), peak HR (HRpeak), percentage of maximum HR (%HRmax), HR variability (HRV), HR recovery (HRR), countermovement jump (CMJ), and psychological responses (rating of perceived exertion [RPE], feeling scale (FS), self-efficacy, intention, enjoyment, preference, and hooper Index) were assessed. Repeated-measures ANOVAs with Bonferroni-adjusted post-hoc tests were conducted (α=0.05). Results: SIT elicited the highest %HRmax and time spent ≥90%HRmax compared with BIT and SIT-BIT (p<0.05), alongside higher RPE (p<0.05) and lower FS scores than BIT (p<0.05). In contrast, BIT induced the lowest %HRmax and more positive perceptual responses (p<0.05). The combined SIT-BIT protocol induced intermediate responses, eliciting higher cardiovascular strain than BIT (p<0.05) while attenuating the increase in RPE observed during SIT (p<0.05). Enjoyment did not differ between protocols (p>0.05), although SIT-BIT was the most frequently preferred condition (p<0.05). CMJ height decreased only after SIT (p<0.05). Conclusion(s): Overall, combining SIT and BIT within a very low-volume session provides a balanced physiological stimulus while improving psychological tolerability compared with SIT alone.