Torque And Emg Evaluation Of The Antagonist Knee Muscles, During a Fatiguing Maximal, Submaximal Isokinetic Protocol And Recovery In Males

Introduction
Many studies in the past have analyzed agonist and antagonist EMG activity of the knee muscles during maximal
isometric and isokinetic fatigue efforts. During maximal isokinetic fatigue efforts it was observed that the antagonist
activity remain stable while during submaximal and maximal isometric fatigue it increases or remain stable respectively
[1,2]. This antagonist activity during fatigue was attributed to various factors, one of them it was speculated that is
fatigue of the antagonist muscle (1,2,3). However this speculation was not studied experimentally. Therefore, the
purpose of this study was to examine the fatigability of antagonist muscles during a maximal and submaximal isokinetic
fatigue test of knee extensors.

Methods
Fourteen healthy males (age: 24,3±2,5y), performed 25 maximal and 60 submaximal isokinetic concentric efforts of the
knee extensors at 60°s -1, for maximal and submaximal protocol respectively, in two different sessions. During both
protocols, maximal extensions-flexions were performed to be used as report values for the evaluation of antagonist
activity. The torque was recorded using the isokinetic dynamometer Cybex Norm. The EMG activity of vastus medialis
(VM), vastus lateralis (VL) and biceps femoris (BF) was recorded using Biopac MP100 through surface electrodes.
Before and after the fatigue test, maximal extensions and flexions were performed in order any alteration of torque and
EMG activity to be evaluated. The torque and average EMG (aEMG) was calculated for each repetition for both
protocols. The torque of BF as agonist, was calculated every ten repetitions for both of protocols. During 15minutes
recovery period a maximal extension and flexion effort was performed every 3min. One-way AnOVa with repeated
measurements was used for each protocol. The level of significance was set at p<0.05.

Results
The torque of agonists demonstrated a significant decline of 45,7% and 46,6% for maximal and submaximal protocol,
respectively. The torque and the activity of BF acting as agonist remained unaltered (p>0.05) in both
protocols. On contrary, extensors aEMG was increased and then decreased in maximal protocol while in
submaximal protocol continuously increased (p<0.05). At the end of the recovery period, the torque and
activity of BF muscles remained unaltered. On the contrary torque and EMG activity of extensors gradually
increased reaching the 90% of the prefatigue value.

Discussion / Conclusions
A maximal and submaximal isokinetic protocol it seems that does not affect torque production of the antagonist
muscles. Thus, it can be assumed that the antagonist activity is regulated mainly by neuronal factors.

References
[1] Kellis E. & Kellis S. (2001). J Electromyogr Kinesiol,11, 307-318
[2] Kellis E. (1999). J Electromyogr Kinesiol, 9, 191-199
[3] Mullany et al (2002). J Electromyogr Kinesiol,12, 375-384

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