Vol. 7, Issue 2, Part C (2025)

Background: High-intensity interval training (HIIT) is widely promoted as a time-efficient method to enhance cardiorespiratory fitness, yet collegiate athletes operate within congested in-season calendars where conditioning time and recovery capacity are limited. Evidence specific to collegiate populations and practical HIIT prescription remains comparatively sparse.

Objective: To determine the effects of an 8-week HIIT mesocycle on cardiovascular endurance in collegiate athletes, using VO₂max as the primary outcome and Yo-Yo Intermittent Recovery Test Level-1 (Yo-Yo IR1) as a secondary sport-specific endurance marker.

Methods: In a randomized controlled pre-post design, 48 university athletes (18-24 years) were stratified by sport and sex and allocated to HIIT plus usual training or usual training alone. The HIIT group completed three supervised sessions weekly for 8 weeks using a long-interval 4×4-min protocol at 90-95% HR_max with 3-min active recoveries. VO₂max was assessed via graded treadmill testing with breath-by-breath gas analysis, and intermittent endurance via Yo-Yo IR1. Training intensity and internal load were monitored by heart rate and session RPE. Mixed ANOVA evaluated group×time effects, with effect sizes reported.

Results: Forty-four athletes completed the intervention (HIIT n=22, control n=22). Baseline characteristics were comparable between groups. A significant group×time interaction was observed for VO₂max, with the HIIT group improving by 8.1% (56.3±4.1 to 60.9±4.5 mL·kg⁻¹·min⁻¹; p<0.001; d=1.10) compared with trivial change in controls (1.1%; p=0.19). Yo-Yo IR1 performance increased by 17.3% in HIIT (p<0.001; d=0.88) versus 4.2% in controls (p=0.07). Responder rates favored HIIT for both VO₂max and Yo-Yo criteria, and no serious adverse events occurred.

Conclusion: A short, periodized 8-week HIIT mesocycle added to routine collegiate training produces large, practically meaningful improvements in cardiovascular endurance and intermittent field performance, supporting HIIT as a highly efficient conditioning strategy for collegiate athletes during in-season periods.