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2001 Publications

Electromyographic analysis of quadriceps fatigue after anterior cruciate ligament reconstructionby McHugh MP, Tyler TF, Nicholas SJ, Browne MG, Gleim GW. - last modified 2012-11-27 00:00
Journal of Orthopedic and Sports Physical Therapy. 31: 25-32, 2001.


Study Design: Prospective, observational study.

Objectives: To document changes in surface EMG activity during sustained maximum quadriceps contractions in patients prior to and five weeks following anterior cruciate ligament (ACL) reconstruction.

Background: Quadriceps weakness is well documented following injury and reconstruction of the ACL. However, the effect of weakness on muscle fatigue is not well understood.

Methods and Measures: EMG signals were recorded from the vastus lateralis, vastus medialis and rectus femoris muscles during 30 s maximum isometric contractions at 30°, in 42 patients preoperatively, and five weeks postoperatively. Signal amplitude was quantified by integrating the rectified signal (iEMG) for the initial and final 5 s and comparing the involved and uninvolved sides. Median frequency (MF) was computed from 4096 point fast Fourier Transforms performed at the beginning and end of the 30 s contractions. Results: Patients had moderate preoperative quadriceps weakness (16% deficit) and gross postoperative weakness (41% deficit). Weakness was associated with deficits in both median frequency (MF) and iEMG (R=0.69-0.67). During the preoperative fatigue test torque declined similarly on the involved and uninvolved sides (significant fatigue effect). However, during the postoperative fatigue tests torque increased on the involved side and declined on the uninvolved side (significant side by fatigue interaction). For the initial 5 s, MF was lower on the involved than the uninvolved side but subsequently showed a smaller decline over 30 s preoperatively and postoperatively (significant side by fatigue interactions). IEMG was lower on the involved side preoperatively and postoperatively. During the fatigue tests iEMG increased similarly in the involved and uninvolved sides both preoperatively and postoperatively.

Conclusion: Based on these results, quadriceps endurance exercises are not indicated following ACL reconstruction. Quadriceps weakness following ACL reconstruction was associated with fatigue resistance. Lower initial MF and smaller decline in MF during sustained contraction is consistent with fast-twitch fiber atrophy and would explain fatigue resistance.