School of Sport, Exercise and Health Sciences, Loughborough University , Loughborough , United Kingdom.
J Appl Physiol (1985). 2018 Sep 1;125(3):737-745. doi: 10.1152/japplphysiol.01126.2017. Epub 2018 Jun 7.
The asymptote [critical power (CP)] and curvature constant ( W') of the hyperbolic power-duration relationship can predict performance within the severe-intensity exercise domain. However, the extent to which these parameters relate to skeletal muscle morphology is less clear, particularly in endurance-trained individuals, who, relative to their lesser-trained counterparts, possess skeletal muscles that can support high levels of oxygen transport and oxidative capacity, i.e., elevated type I fiber proportion and cross-sectional area (CSA) and capillarity. Fourteen endurance-trained men performed a maximal incremental test to determine peak oxygen uptake (V̇o; 63.2 ± 4.1 ml·min·kg, mean ± SD) and maximal aerobic power (406 ± 63 W) and three to five constant-load tests to task failure for the determination of CP (303 ± 52 W) and W' (17.0 ± 3.0 kJ). Skeletal muscle biopsies were obtained from the vastus lateralis and analyzed for percent proportion of fiber types, CSA, and indexes of capillarity. CP was positively correlated with the percent proportion ( r = 0.79; P = 0.001) and CSA ( r = 0.73; P = 0.003) of type I fibers, capillary-to-fiber ratio ( r = 0.88; P < 0.001), and capillary contacts around type I fibers ( r = 0.94; P < 0.001) and type II fibers ( r = 0.68; P = 0.008). W' was not correlated with any morphological variables. These data reveal a strong positive association between CP and skeletal muscle capillarity. Our findings support the assertion that CP is an important parameter of aerobic function and offer novel insights into the physiological bases of CP. NEW & NOTEWORTHY This investigation demonstrated very strong positive correlations between critical power and skeletal muscle capillarity, particularly around type I fibers, and type I fiber composition. These correlations were demonstrated in endurance-trained individuals expected to possess well-adapted skeletal muscles, such as high levels of oxygen transport structures and high oxidative capacities, supporting the view that critical power is an important parameter of aerobic function. In contrast, the curvature constant W' was not associated with fiber type composition or capillarity.
渐近线[临界功率（CP）]和曲率常数（W'）的双曲幂律关系可以预测剧烈强度运动域内的性能。然而，这些参数与骨骼肌形态的关系尚不清楚，尤其是在耐力训练的个体中，与他们相比，耐力训练的个体拥有能够支持高水平氧气输送和氧化能力的骨骼肌，即高比例的 I 型纤维和横截面积（CSA）和毛细血管。14 名耐力训练的男性进行了最大递增测试，以确定峰值摄氧量（V̇o；63.2±4.1ml·min·kg，平均值±SD）和最大有氧功率（406±63W），并进行了三到五次恒负荷测试，以确定 CP（303±52W）和 W'（17.0±3.0kJ）的衰竭。从股外侧肌获得骨骼肌活检，并分析纤维类型、CSA 和毛细血管指数的百分比。CP 与 I 型纤维的百分比（ r=0.79；P=0.001）和 CSA（ r=0.73；P=0.003）、毛细血管与纤维比（ r=0.88；P<0.001）、I 型纤维周围的毛细血管接触（ r=0.94；P<0.001）和 II 型纤维（ r=0.68；P=0.008）呈正相关。W'与任何形态变量都没有相关性。这些数据显示 CP 与骨骼肌毛细血管之间存在很强的正相关。我们的研究结果支持 CP 是有氧功能的重要参数的观点，并为 CP 的生理基础提供了新的见解。新的和值得注意的是这项研究表明，临界功率与骨骼肌毛细血管之间存在很强的正相关，特别是在 I 型纤维周围和 I 型纤维组成方面。这些相关性在预期具有良好适应的骨骼肌的耐力训练个体中得到了证明，例如高水平的氧气输送结构和高氧化能力，这支持了临界功率是有氧功能的重要参数的观点。相比之下，曲率常数 W'与纤维类型组成或毛细血管无关。
