Center for Sensory-Motor Interaction, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
J Electromyogr Kinesiol. 2012 Jun;22(3):342-7. doi: 10.1016/j.jelekin.2012.01.014. Epub 2012 Feb 24.
Muscle fatigue is associated with reduced power output and work capacity of the skeletal muscle. Fatigue-induced impairments in muscle function are believed to be a potential cause of increased injury rates during the latter stages of athletic competition and often occur during unexpected perturbations. However the effect of fatigue on functionally relevant, full body destabilizing perturbations has not been investigated. This study examines the effect of muscle fatigue on the activation of the quadriceps and hamstrings to fast, full body perturbations evoked by a moveable platform. Surface electromyographic (EMG) signals were recorded from the knee extensor (vastus medialis, rectus femoris, and vastus lateralis) and flexor muscles (biceps femoris and semitendinosus) of the right leg in nine healthy men during full body perturbations performed at baseline and immediately following high intensity exercise performed on a bicycle ergometer. In each condition, participants stood on a moveable platform during which 16 randomized postural perturbations (eight repetitions of two perturbation types: 8 cm forward slides, 8 cm backward slides) with varying inter-perturbation time intervals were performed over a period of 2-3 min. Maximal voluntary knee extension force was measured before and after the high intensity exercise protocol to confirm the presence of fatigue. Immediately after exercise, the maximal force decreased by 63% and 66% for knee extensors and flexors, respectively (P<0.0001). During the post-exercise postural perturbations, the EMG average rectified value (ARV) was significantly lower than the baseline condition for both the knee extensors (average across all muscles; baseline: 19.7±25.4μV, post exercise: 16.2±19.4 μV) and flexors (baseline: 24.3±20.9 μV, post exercise: 13.8±11.0 μV) (both P<0.05). Moreover the EMG onset was significantly delayed for both the knee extensors (baseline: 132.7±32.9 ms, post exercise: 170.8±22.9 ms) and flexors (baseline: 139.1±38.8 ms, post exercise: 179.3±50.9 ms) (both P<0.05). A significant correlation (R(2)=0.53; P<0.05) was identified between the percent reduction of knee extension MVC and the percent change in onset time of the knee extensors post exercise. This study shows that muscle fatigue induces a reduction and delay in the activation of both the quadriceps and hamstring muscles in response to rapid destabilizing perturbations potentially reducing the stability around the knee.
肌肉疲劳会导致骨骼肌的功率输出和工作能力降低。人们认为，疲劳导致的肌肉功能障碍是运动竞赛后期受伤率增加的一个潜在原因，而且这种情况经常在意外的扰动中发生。然而，疲劳对功能相关的、全身性的不稳定扰动的影响尚未得到研究。本研究探讨了肌肉疲劳对快速全身扰动时股四头肌和腘绳肌激活的影响，这些扰动是由可移动平台引起的。在 9 名健康男性的右侧腿上，记录了膝伸肌（股直肌、股外侧肌和股中间肌）和屈肌（股二头肌和半腱肌）的表面肌电图（EMG）信号，这些信号是在基线和高强度自行车测力计运动后立即进行全身扰动时获得的。在每种情况下，参与者都站在一个可移动的平台上，在此期间，平台执行了 16 个随机的姿势扰动（8 次向前滑动，8 次向后滑动），每个扰动之间的时间间隔不同，持续 2-3 分钟。在高强度运动方案前后测量最大自愿膝关节伸展力，以确认疲劳的存在。运动后，膝关节伸肌和屈肌的最大力分别下降了 63%和 66%（P<0.0001）。在运动后的姿势扰动中，与基线相比，EMG 平均整流值（ARV）在所有肌肉中均显著降低（平均值；基线：19.7±25.4μV，运动后：16.2±19.4 μV）和屈肌（基线：24.3±20.9 μV，运动后：13.8±11.0 μV）（均 P<0.05）。此外，膝关节伸肌（基线：132.7±32.9 ms，运动后：170.8±22.9 ms）和屈肌（基线：139.1±38.8 ms，运动后：179.3±50.9 ms）的 EMG 起始时间均显著延迟（均 P<0.05）。在膝关节伸肌（R（2）=0.53；P<0.05）和膝关节伸肌（R（2）=0.53；P<0.05）之间，最大膝关节伸展 MVC 的降低百分比与运动后膝关节伸肌起始时间的变化百分比之间存在显著相关性。本研究表明，肌肉疲劳会导致股四头肌和腘绳肌的激活减少和延迟，从而对快速的不稳定扰动做出反应，可能会降低膝关节周围的稳定性。
