Department of Kinesiology and Health Education, University of Texas at Austin, TX, USA.
J Electromyogr Kinesiol. 2011 Feb;21(1):25-32. doi: 10.1016/j.jelekin.2010.09.002. Epub 2010 Oct 12.
Local muscle fatigue may be related to potassium efflux from the muscle cell and/or lactate accumulation within the muscle. Local fatigue causes a decrease in median frequency (MPF) of the electromyogram's power spectrum during isometric contractions but its relationship to changes in potassium and lactate during dynamic exercise is equivocal. Thus, this investigation evaluated relationships between changes in the MPF from the vastus lateralis and blood levels of lactate and potassium during an incremental cycling test and recovery. Trained cyclists (n=8) completed a discontinuous, graded cycle test to exhaustion under normal and glycogen-reduced conditions. The glycogen reduced condition promoted an environment of lower lactate production while permitting a consistent potassium response. Blood samples and maximal isometric EMG data were collected at the end of each stage and during recovery. Maximal lactate levels were ∼ 60% lower in the glycogen reduced condition; potassium was similar between trials. MPF did not change significantly at volitional fatigue. Further, MPF was not significantly related to lactate (p>0.27) or potassium (p>0.16) in either condition. Though both lactate and potassium have been implicated as factors relating to local muscle fatigue, neither is significantly related to changes in MPF during or after progressive exercise on a cycle ergometer.
局部肌肉疲劳可能与钾从肌肉细胞中流出和/或肌肉内乳酸积累有关。在等长收缩期间，局部疲劳会导致肌电图功率谱的中值频率 (MPF) 降低，但它与动态运动期间钾和乳酸的变化关系尚不清楚。因此，本研究评估了递增循环测试和恢复期间股外侧肌 MPF 变化与血液中乳酸和钾水平之间的关系。经过训练的自行车运动员（n=8）在正常和糖原减少条件下完成了不连续的分级循环测试直至力竭。糖原减少的条件促进了低乳酸产生的环境，同时允许钾的一致反应。在每个阶段结束时和恢复期间收集血样和最大等长肌电图数据。最大乳酸水平在糖原减少的条件下降低了约 60%；钾在两次试验之间相似。在自愿疲劳时，MPF 没有明显变化。此外，在两种情况下，MPF 与乳酸（p>0.27）或钾（p>0.16）均无显著相关性。尽管乳酸和钾都被认为是与局部肌肉疲劳相关的因素，但在递增运动自行车上进行的渐进性运动期间或之后，它们都与 MPF 的变化没有显著关系。
