Rectus femoris M. fatigability and recovery from prolonged maximal isometric voluntary contracti̇ons

Background: An increase in amplitude measurements of electromyographic (EMG) signals and a decrease in the average frequency of the EMG power spectrum are used to evaluate neuromuscular fatigue. In this study, we investigated the fatigue and recovery processes in the rectus femoris (RF) muscle during prolonged submaximal voluntary isometric contractions using EMG signals. Method: In this study, 12 male and 12 female participants performed voluntary isometric contractions with their knee extensors on an isokinetic dynamometer. Firstly, the maximal voluntary contraction (MVC) levels of the participants were determined during maximal isometric knee extension test. Then, 4- minute isometric contractions were repeated 3 times at 15% of the MVC. A 10-minute recovery interval was given between the repetitions. Visual feedback was provided on a separate screen to enable participants to sustain their isometric contractions. The EMG data for the RF muscle was collected using a pair of electrodes attached to the skin and wirelessly transferred to a computer during all the measurements. EMG and torque data were recorded simultaneously. The mean and median frequencies of the 4-minute (× 3 repetitions) unprocessed EMG data were calculated for 2- second windows and the averages of each repetition were calculated. Results and Conclusion: We found that there were indicators of fatigue in the RF muscle after 4 minute submaximal voluntary contractions, but the rest intervals given between the sets were sufficient for recovery. As a result, this study shows that a 10-minute rest period is sufficient for RF muscle to recover during 4-minute voluntary isometric contractions. Keywords: Physical fatigue, Voluntary contraction, Nervous system, Muscle function.