Continuous Peak Oxygen Uptake Monitoring in High-Intensity Interval Training Minimizes False Responder Rates Compared to Pre-to-Post Testing.

Abstract

Purpose: This study investigates the intra- and inter-individual time courses of physiological adaptation to high-intensity interval training (HIIT), comparing single and duplicate pre-to-post testing with session-by-session analysis to more accurately identify "genuine" adaptations.

Methods: Seventeen participants (nine men) engaged in repeated 4x4 min HIIT sessions (2 times/week) until a meaningful change in the primary outcome i.e. relative peak oxygen uptake (VO2peak) was observed.

Results: Mixed-effects model analysis revealed a significant improvement for VO2peak for both session-by-session (estimate: 0.18, p < 0.01, d = 0.11) analysis and duplicate pre-to-post analysis (estimate: 3.97, p < 0.01, ηp2 = 0.36). Session-by-session analysis revealed significant variability in physiological responses, with a low coefficient of variation (CV) for VO2peak (3.49% + 1.96) and estimated maximum stroke volume (SVmax) (3.07% ± 1.92) and, indicating their reliability for detecting small changes. With a CV of 22.14% ± 13.80 submaximal blood lactate ([BLa]submax) was the least reliable parameter. With session-by-session analysis VO2peak was the only parameter displaying 100% positive responders after 9.5 ± 3.8 sessions. Additionally, session-by-session analysis revealed lower proportions of participants with positive adaptations for submaximal VO2 and SVmax, but higher proportions for submaximal respiratory exchange ratio and rating of perceived exertion compared with pre-to-post analysis.

Conclusions: This study highlights the value of longitudinal assessments for understanding the variability and dynamics of training adaptations. By addressing the limitations of pre-to-post evaluations, the findings emphasize the importance of frequent monitoring to accurately capture individual responses, thereby advancing strategies for optimizing exercise interventions across diverse populations.