Research Institute MOVE, VU University Amsterdam, The Netherlands.
Med Sci Sports Exerc. 2012 Jul;44(7):1366-74. doi: 10.1249/MSS.0b013e318249d701.
Above a given exercise intensity, rapid muscle fatigue will occur. We explored the possibility of assessing torque threshold for peripheral fatigue during single-legged repetitive isometric knee extensor exercise. We hypothesized this fatigue threshold to be related to the general aerobic fitness level and the so-called "critical torque" (CT) established with a recently validated 5-min all-out test.
Seventeen healthy men (VO(2max) = 44.7-69.6 mL·kg(-1)·min(-1)) performed six submaximal (20%-55% maximal voluntary contraction [MVC]) 5-min bouts of 60 repetitive contractions (3-s on, 2-s off). Torque was changed between bouts in steps of 5% MVC to estimate the highest intensity (fatigue threshold) at which average changes in rsEMG, EMG median power frequency, and tissue deoxygenation (near-infrared spectroscopy) of the three superficial knee extensor muscles were still <5%, signifying steady-state exercise with minimal peripheral fatigue. On another occasion, one bout was performed in an all-out manner with end-test torque representing CT.
Fatigue threshold (40.0% ± 8.1% MVC) was related (r(2) = 0.57, P < 0.05) to CT (53.1% ± 10.0% MVC), but it was consistently lower (P < 0.05) and only fatigue threshold was significantly related to VO(2max) (r(2) = 0.68), and the first (r(2) = 0.45) and second (r(2) = 0.63) ventilatory threshold obtained during cycle ergometry.
Performing submaximal bouts of knee extensor contractions, while monitoring EMG and deoxygenation, seems a feasible manner to estimate an aerobic capacity-related exercise intensity of peripheral fatigue onset. This test may be used to evaluate changes in endurance capacity of single muscle groups, without the necessity for all-out testing, which could be problematic with frail subjects.
在给定的运动强度之上，会迅速出现肌肉疲劳。我们探讨了在单腿重复等长膝伸肌运动中评估外周疲劳时的扭矩阈值的可能性。我们假设这种疲劳阈值与一般有氧健身水平和最近验证的 5 分钟全力测试中建立的所谓“临界扭矩”（CT）有关。
17 名健康男性（VO₂max=44.7-69.6 mL·kg⁻¹·min⁻¹）进行了 6 次亚最大（20%-55%最大随意收缩[MVC]）5 分钟 60 次重复收缩的运动，每组 3 秒收缩，2 秒休息。在各运动之间以 5%MVC 的步长改变扭矩，以估计平均肌电图（rsEMG）、肌电图中位功率频率和三个浅层膝伸肌组织去氧（近红外光谱）的变化仍<5%的最高强度（疲劳阈值），这表示运动处于稳态，外周疲劳最小。在另一次测试中，一次运动以全力进行，末端测试扭矩代表 CT。
疲劳阈值（40.0%±8.1%MVC）与 CT（53.1%±10.0%MVC）相关（r²=0.57，P<0.05），但始终较低（P<0.05），只有疲劳阈值与 VO₂max 显著相关（r²=0.68），以及在循环测功机上获得的第一（r²=0.45）和第二（r²=0.63）通气阈值。
在监测肌电图和去氧的情况下，进行亚最大的膝伸肌收缩运动似乎是一种可行的方法，可以估计与有氧能力相关的外周疲劳起始运动强度。这种测试可用于评估单一肌肉群耐力能力的变化，而无需进行全力测试，这对于虚弱的受试者来说可能是个问题。
Zotero 插件