Muscle fatigue assessment has been the basis of numerous studies, specifically, in neuromuscular rehabilitation and the applications of FESsystems. Various EMGbased techniques, in time and frequency domains, have been investigatedover years for the detection and evaluationof this phenomenon. The main objective of this study has beento evaluate the efficiency of applying a number of techniques which have been mostly applied to detect fatigue in isometric contractions,for the assessment ofthis phenomenon in repetitive isotonic experiments.Twogroups of tasks were devised to produce both types of contractions in two muscle groups, Biceps and Deltoid. Simultaneously, the relevant sEMG signalswere recorded anda number of time-domainindices(RMS, ARV, and ZC), together with two frequencybased features:mean and median frequency, were extracted from the recorded samples.The resulted diagramsfor all the contractionsrevealed an overall increase in the values of time domain features,and a decline in ZC and the quantities of frequencycomponents;however, the frequency-based indices represented smoother trends and, therefore, showed to be better representatives of the fatiguing phenomenon. It was also observed that, generally, the diagrams belonging to isotonic exercises stood at lower levels in comparison to the isometric ones,which mainly stem from the resting periods existing in the isotonic tasks.In the final step,theapproach utilized by Seibt and Schneider,toward representinga quantitative portrayal of muscle fatigue,was applied to the recorded signals and the deficitsinherently existing in similar approacheswerereviewed from various aspects.