Desbrosses Kévin, Babault Nicolas, Scaglioni Gil, Meyer Jean-Peerre, Pousson Michael
INSERM/ERIT-M Motricity-Plasticity, Faculty of Sport Science, University of Burgundy, Dijon, France.
Med Sci Sports Exerc. 2006 May;38(5):937-44. doi: 10.1249/01.mss.0000218136.58899.46.
To investigate i) whether neural activation dependence on muscle length is preserved with neuromuscular fatigue and ii) whether fatigue induced by a maximal isometric exercise is muscle length dependent.
Twelve male subjects performed two fatiguing quadriceps muscle exercises: FS is the fatigue carried out at short muscle length (S) (S = 40 degrees of knee flexion) and FL is the fatigue at long muscle length (L) (L = 100 degrees). Before and after each fatiguing exercise (i.e., three maximal isometric contractions maintained until 80, 60, and 40% of the initial maximal torque, respectively), activation level (AL, assessed by means of twitch interpolation technique), EMG activity (RMS), and peak doublet torque (Pd) were measured at the two lengths (S and L).
First, AL was greater (P < 0.05) at L compared with S before and after both exercises. Second, despite a similar decrease in maximal voluntary torque (approximately 21% of the initial value) after the two exercises, AL and RMS were significantly reduced after FS (P < 0.05) but remained unchanged after FL, whereas the Pd decrease was more pronounced after FL than FS (P < 0.05). Nevertheless, after a given fatiguing exercise (i.e., FS or FL), AL, RMS, and Pd changes were similar at both postexercise test lengths (S and L).
These results clearly demonstrate that i) the neural activation dependence on quadriceps muscle length is maintained with fatigue, and ii) neuromuscular fatigue after maximal isometric contractions is dependent on the muscle length at which the exercise is performed: short length preferentially induces neural activation impairment, whereas long length leads to higher contractile failure.
研究i）神经激活对肌肉长度的依赖性在神经肌肉疲劳时是否保持，以及ii）最大等长运动诱导的疲劳是否依赖于肌肉长度。
12名男性受试者进行了两种使股四头肌疲劳的运动：FS是在短肌肉长度（S）（S = 膝关节屈曲40度）下进行的疲劳运动，FL是在长肌肉长度（L）（L = 100度）下进行的疲劳运动。在每次疲劳运动前后（即分别保持三次最大等长收缩直至初始最大扭矩的80%、60%和40%），在两个长度（S和L）下测量激活水平（AL，通过抽搐插值技术评估）、肌电图活动（RMS）和双峰扭矩峰值（Pd）。
首先，在两种运动前后，L处的AL均高于S处（P < 0.05）。其次，尽管两种运动后最大自主扭矩有相似程度的下降（约为初始值的21%），但FS后AL和RMS显著降低（P < 0.05），而FL后保持不变，并且FL后Pd的下降比FS更明显（P < 0.05）。然而，在进行给定的疲劳运动（即FS或FL）后，运动后测试的两个长度（S和L）处的AL、RMS和Pd变化相似。
这些结果清楚地表明，i）神经激活对股四头肌长度的依赖性在疲劳时得以维持，并且ii）最大等长收缩后的神经肌肉疲劳取决于运动时的肌肉长度：短长度优先诱导神经激活受损，而长长度导致更高的收缩性衰竭。
