Does Hormonal Phase Affect Acute High-Intensity Interval Training Exercise? An Evaluation of Performance and Fatigue

Moore, SR, Joniak, KE, Ladan, AN, Britton, ME, Cantu, EI, Hirsch, KR, Hackney, AC, and Smith-Ryan, AE. Does hormonal phase affect acute high-intensity interval training exercise? An evaluation of performance and fatigue. J Strength Cond Res 40(9): e901-e908, 2026-Fatigue is a critical factor in high-intensity interval training (HIIT) performance, which may vary across female hormonal phases and with changes in work-rest ratio. This study evaluated exercise performance (average power [AP], peak power [PP]) and fatigue (power drop [PD; peak power-minimum power/time]) between 2 work-matched HIIT protocols during the low- (LHP) and high-hormone phases (HHP). In total, 35 women (age: 24.3 ± 6.1 years) completed 4 HIIT trials in randomized orders of hormonal phase and HIIT protocol: HIIT 1:1 : 10 rounds of 1 minute on/1 minute off; HIIT 2:1 : 20 rounds of 20 s on/10 s off. High-intensity interval training 2:1 resulted in significantly higher AP (HIIT 1:1 -HIIT 2:1 Δ-36.6 ± 2.3 W; p < 0.001) and PP (Δ-34.1 ± 4.0 W; p < 0.001) than HIIT 1:1 , with no significant difference between phase differences. When analyzed by protocol, HIIT 2:1 demonstrated greater PD in the LHP than in the HHP (Δ11.4 ± 4.7 W; p = 0.020), with no significant difference between phases for HIIT 1:1 . When collapsed across protocols, PD was significantly greater in the LHP than in the HHP (LHP-HHP Δ11.2 ± 4.9 W·s -1 ; p = 0.031). High-intensity interval training power performance (AP, PP) was influenced by the work-rest ratio, but not hormonal phase, with significantly higher power output in HIIT 2:1 . Greater PD during the LHP suggests physical fatigue may vary across hormonal phases, but the lack of HIIT 1:1 PD differences between phases may indicate augmented recovery with the equal work-rest ratio, particularly during the LHP. Although power performance was minimally different between phases, altering work-rest ratio may be a consideration for maintaining power outcomes and managing fatigue across female hormonal cycles, particularly in the LHP.