Twitch potentiation after voluntary contraction and neuromuscular electrical stimulation at various frequencies in human quadriceps femoris

Introduction: In this study we aimed to compare the extent of twitch potentiation (TP) after voluntary contraction and percutaneous electrical stimulation of muscles (neuromuscular electrical stimulation: NMES) with various stimulation frequencies at equivalent target levels. Methods: Isometric knee extensions of 10 s were performed at a 40% maximal voluntary contraction level by voluntary or NMES conditioning contractions at 20, 40, and 80 HZ of the quadriceps femoris muscle. Twitch responses were elicited by stimulating the femoral nerve transcutaneously at supramaximal intensity. Results: NMES at 80 HZ induced significantly less TP (128.7 +/- 17.1%) than voluntary contraction (156.2 +/- 23.1%), whereas no statistical difference was found in TP among voluntary and 20- and 40-HZ NMES conditioning contractions (170.8 +/- 21.1% and 162.7 +/- 16.9% for 20- and 40-HZ NMES, respectively). Conclusion: Stimulation frequency of NMES determines whether NMES can induce TP comparable to that after voluntary contraction. Muscle Nerve 45: 110115, 2012