Impact of High-Intensity Interval Training (HIIT) on Cardiovascular Endurance in Collegiate Athletes

Abstract

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