Durability of the moderate-to-heavy intensity transition can be predicted using readily available markers of physiological decoupling

Abstract

Purpose: To assess relationships between heart rate (HR), ventilation (̇V˙E), and respiratory frequency (FR) decoupling and durability of the first ventilatory threshold (VT1), and the strength of practical models to predict power output at VT1 during prolonged exercise. Methods: Durability of VT1 was assessed via measurements of power output at VT1 before and after ~ 2.5-h of initially moderate-intensity cycling in 51 trained cyclists, as part of four studies published elsewhere. In 12 of those participants, power output at VT1 was assessed every hour until task failure. For every assessment of power output at VT1, HR, FR, and V˙̇E was measured at fixed power outputs, and thus decoupling of these variables with power output was determined. Bivariate repeated-measures correlations (rrm) between decoupling and durability of VT1 were assessed. Multivariable models were created to predict power output at VT1 during prolonged exercise using generalised estimating equations. Results: Negative correlations were observed between exercise-induced change in power output at VT1 and HR (rrm = −0.76, P < 0.001) and FR (rrm = −0.40, P = 0.013) decoupling, but not V˙̇E decoupling (rrm = −0.25, P = 0.136). The final prediction model, containing baseline VT1 and peak oxygen uptake, FR decoupling, and an interaction between HR decoupling and exercise duration, effectively predicted real-time VT1 (mean absolute error, ~ 7.2 W; R2, 0.95). Conclusion: HR and/or FR decoupling during controlled training sessions may be a practically useful durability assessment. Our prediction models may be an effective means of improving within-session intensity regulation and training load monitoring.