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 (Ѷᴇ), and respiratory frequency (Fꭆ) 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, Fꭆ, and Ѷᴇ 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 Fꭆ (rᵣₘ = −0.40, P = 0.013) decoupling, but not Ѷᴇ decoupling (rᵣₘ = −0.25, P = 0.136). The final prediction model, containing baseline VT₁ and peak oxygen uptake, Fꭆ 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 Fꭆ 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.