Yuri Feito

High-intensity interval training (HIIT) is an effective alternative to moderate intensity continuous training for improvements in body composition and aerobic capacity; however, there is little work comparing different modalities of HIIT. The purpose of this study was to compare the effects of plyometric- (PLYO) and cycle-oriented (CYC) HIIT on body composition, aerobic capacity, and skeletal muscle size, quality, and function in recreationally trained females. Young (21.7 ± 3.1 yrs), recreationally active females were quasi-randomized (1:1 ratio) to 8 weeks of twice weekly PLYO ( n = 15) or CYC ( n = 15) HIIT. Body composition (four-compartment model), VO 2peak , countermovement jump performance, muscle size, and echo intensity (muscle quality), as well as strength and power of the knee extensors and plantar flexors were measured before and after training. Both groups showed a similar decrease in body fat percentage ( p < 0.001; [Formula: see text]= 0.409) and echo intensity ( p < 0.001; [Formula: see text] = 0.558), and an increase in fat-free mass ( p < 0.001; [Formula: see text]= 0.367) and VO 2peak ( p = 0.001; [Formula: see text] = 0.318). Muscle size was unaffected ( p > 0.05), whereas peak torque was reduced similarly in both groups ( p = 0.017; [Formula: see text] = 0.188) and rapid torque capacity was diminished only for the knee extensors after CYC ( p = 0.022; d = −0.67). These results suggest that PLYO and CYC HIIT are similarly effective for improving body composition, aerobic capacity, and muscle quality, whereas muscle function may express moderate decrements in recreationally active females. ClinicalTrials.gov (NCT05821504)