A detailed comparison of oxygen uptake kinetics at a range of exercise intensities

Abstract Aim: The aim of this study was to comprehensively examine oxygen uptake (V̇O2) kinetics during cycling through mathematical modeling of the breath-by-breath gas exchange responses across eight conditions of unloaded cycling to moderate to high-intensity exercise. Methods: Following determination of GET and V̇O2peak, eight participants (age: 24±8y; height: 1.78±0.09m; mass: 76.5±10.1kg; V̇O2peak: 3.89±0.72 L.min-1) completed a series of square-wave rest-to-exercise transitions at; -20%∆ (GET minus 20% of the difference in V̇O2 between that at GET and VO2peak), -10%∆, GET, 10%∆, 20%∆, 30%∆, 40%∆, and 50%∆. The V̇O2 kinetic response was modelled using mono- and bi-exponential non-linear regression techniques. The difference in the standard error of the estimates (SEE) for the mono- and bi-exponential models, and the slope of V̇O2 vs time (for the final minute of exercise) were analysed using paired and one-sample t-tests, respectively. Results: The bi-exponential model SEE was lower than the mono-exponential model across all exercise intensities (p<0.05), indicating a better model fit. Steady-state V̇O2 was achieved across all exercise intensities (all V̇O2 vs. time slopes; p>0.05). The modelled slow component time constants, typical of literature reported values, indicated that the V̇O2 kinetic response would not be completed during the duration of the exercise. Conclusion: It was shown that the addition of the more complex bi-exponential model resulted in a better model fit across all intensities (notably including sub-GET intensities). The slow component phase was incomplete in all cases, even when the investigation of slopes indicated that a steady state had been achieved.

研究目的：本研究旨在通过对8种无负荷骑行至中高强度运动时的逐次呼吸气体交换反应进行数学建模，全面探究骑行过程中的摄氧量（V̇O2）动力学特性。
方法：在测定气体交换阈（Gas Exchange Threshold, GET）与峰值摄氧量（V̇O2peak）后，8名受试者（年龄：24±8岁；身高：1.78±0.09m；体重：76.5±10.1kg；峰值摄氧量：3.89±0.72 L·min⁻¹）完成了一系列方波型静息-运动转换测试，运动强度分别为：-20%Δ（即气体交换阈减去摄氧量峰值与气体交换阈摄氧量差值的20%）、-10%Δ、GET、10%Δ、20%Δ、30%Δ、40%Δ及50%Δ。本研究采用单指数与双指数非线性回归技术对摄氧量动力学反应进行建模。分别采用配对t检验与单样本t检验，对比单指数与双指数模型的估计标准误（Standard Error of the Estimates, SEE）差异，并分析运动最后1分钟的摄氧量-时间斜率。
结果：所有运动强度下，双指数模型的估计标准误均低于单指数模型（p<0.05），表明双指数模型的拟合效果更优。所有运动强度下均达到稳态摄氧量（所有摄氧量-时间斜率均无统计学意义，p>0.05）。建模得到的慢成分时间常数与文献报道的典型值一致，提示摄氧量动力学反应在本次运动持续时间内尚未完成。
结论：研究表明，相较于单指数模型，引入更为复杂的双指数模型可在所有运动强度（包括气体交换阈以下的强度）下获得更优的拟合效果。尽管斜率分析提示已达到稳态，但所有工况下的慢成分阶段均未完成。