Long-Term Physiological Adaptations Induced by Short-Interval High-Intensity Exercises: An RCT Comparing Active and...

Background: High-intensity interval training (HIIT) is one of the most debated methods involving several parameters that could be modulated, but the long-term adaptations it induces are still unclear. This investigation aimed to evaluate the efficacy of running and whole-body exercises with high-intensity (>80% heart rate) short intervals (30 s) in body composition and physical performance and compare the effects between groups with active (AR) or passive recovery (PR), both in males and females. Methods: Eighteen trained young adults (55.56% ♀) were randomly allocated to the PR (n = 9, 23.09 ± 2.56 years, 163.69 ± 9.88 cm, 68.96 ± 14.62 kg) or AR (n = 9, 22.05 ± 1.54 years, 170.61 ± 11.5 cm, 68.78 ± 12.45 kg) group. Both groups performed eight weeks of HIIT, with an equal progression, training, and volume load (TL: F = 1.55, p = 0.214; VL: F = 0.81, p = 0.505). Body fat (BF), fat-free mass (FFM), upper and lower limb fat (UFI, LFI) and muscle areas (UMA, LMA), handgrip strength (HGS), power (countermovement jump, CMJ), agility (5-0-5), and maximal oxygen consumption (V˙O_2p) were tested before and after treatments. Results: The proposed HIIT reduced BF by 9.57% and increased FFM by 2.09%. Females reported better adaptations in LMA (8.34 times higher than males), while both sexes' upper limb mass distribution was better affected by PR (♀: UFI g = 1.851, 95% CI: 0.51, 3.14; ♂: UFI g = 2.456, 95% CI: 0.336, 4.487). Concerning conditioning, the protocol increased V˙O_2p by 6.47%. Females showed better adaptations in CMJ (RR = 1.8), while males showed better adaptations in agility (RR = 3.76). The interaction effects were significant for PR females (right = +6.28%; left = +9.28%) and for AR males (right = +19.21%; left = +19.04%) in HGS. Conclusions: Short-interval HIIT with different exercise recovery types may be a practical solution in training where several physiological improvements are needed. Coaches and trainers can take advantage of the versatile nature of HIIT, relying on desired movement patterns and long-term responses in both male and female individuals.