Department of Physical Performance, Norwegian School of Sport Sciences, Oslo, Norway.
Department of Physics, University of Oslo, Oslo, Norway.
J Appl Physiol (1985). 2022 Jun 1;132(6):1480-1488. doi: 10.1152/japplphysiol.00570.2021. Epub 2022 Apr 28.
This study presents and evaluates a new mathematical model of V̇o on-kinetics, with the following properties: ) a progressively slower primary phase following the size-principle of motor unit recruitment, explaining the delayed V̇o steady state seen in the heavy exercise intensity domain, and ) a severe-domain slow component modeled as a time-dependent decrease in efficiency. Breath-by-breath V̇o measurements from eight subjects performing step cycling transitions, in the moderate, heavy, and severe exercise domains, were fitted to the conventional three-phase model and the new model. Model performance was evaluated with a residual analysis and by comparing Bayesian (BIC) and corrected Akaike (AICc) information criteria. The residual analysis showed no systematic deviations, except perhaps for the initial part of the primary phase. BIC favored the new model, being 9.3 (SD 7.1) lower than the conventional model whereas AICc was similar between models. Compared with the conventional three-phase model, the proposed model distinguishes between the kinetic adaptations in the heavy and severe domains by predicting a delayed steady-state V̇o in the heavy and no steady-state V̇o in the severe domain. This allows to determine when stable oxygen costs of exercise are attainable and it also represents a first step in defining time-dependent oxygen costs when stable energy conversion efficiency is not attainable. We propose and assess a new minimalistic integrated model for the V̇o on-kinetics, inspired by the currently available best evidence of the underlying mechanisms. We show that the model provides a similar fit as the conventionally used three-phase model, even though a stricter data fitting method is used for the proposed model. The proposed model clarifies misconceptions related to the V̇o slow component's behavior, by clearly predicting that steady-state V̇o is attainable in the moderate and heavy exercise intensity domains. Furthermore, the model opens new possibilities for assessing oxygen cost during severe intensity exercise without the fallible assumption of time-constant energy-conversion efficiency.
本研究提出并评估了一种新的 V̇o 动力学数学模型，具有以下特性：) 遵循运动单位募集的大小原则的渐进较慢的初始相，解释了在高强度运动域中观察到的延迟 V̇o 稳定状态，和) 作为效率随时间降低的严重域慢成分建模。对八名受试者在中度、高强度和严重运动域中进行台阶式循环过渡时的逐口气 V̇o 测量值，使用常规三相模型和新模型进行拟合。通过残差分析和比较贝叶斯 (BIC) 和校正的赤池信息量准则 (AICc) 来评估模型性能。残差分析显示没有系统偏差，除了初始相的初始部分。BIC 倾向于新模型，比常规模型低 9.3(SD7.1)，而 AICc 在模型之间相似。与常规三相模型相比，所提出的模型通过预测在高强度域中延迟的 V̇o 稳定状态而在严重域中没有稳定的 V̇o 来区分高强度和严重域中的动力学适应。这允许确定何时可以达到稳定的运动氧耗成本，并且当无法达到稳定的能量转换效率时，它还代表了定义随时间变化的氧耗成本的第一步。我们提出并评估了一种新的最小化整合模型，用于 V̇o 动力学，该模型受到当前可用的潜在机制最佳证据的启发。我们表明，该模型提供了与常规使用的三相模型相似的拟合度，尽管为所提出的模型使用了更严格的数据拟合方法。所提出的模型通过清楚地预测在中度和高强度运动强度域中可以达到 V̇o 稳定状态，澄清了与 V̇o 慢成分行为相关的误解。此外，该模型为在严重强度运动期间评估氧耗成本提供了新的可能性，而无需依赖时间常数能量转换效率的不可靠假设。
