This study aimed to assess the utility of peak counting in dynamic muscle contractions. Surface electromyog-raphy (sEMG) data were collected from three quadriceps femoris muscles of twelve healthy individuals during 50 repeated isokinetic knee extensions. The level of muscle fatigue was quantified by applying peak counting, mean frequency (MNF), and median frequency (MDF) to sEMG signals, and a fatigue index value was extracted for each parameter. The Bland-Altman plots were used to show the agreement between the methods based on the fatigue index values. The relationship between MNF, MDF and number of peaks (NoP) was described by using linear regression models. The results showed that the peak counting method measures the fatigue level of the muscles equivalent to MNF and MDF in terms of fatigue index values. The peak counting method has a stronger rela-tionship with MNF than MDF, considering the R-squared values of the linear regression models. In conclusion, peak counting was found to be a valid method, and the NoP was evaluated as a reliable parameter in the quantitative analysis of muscle fatigue during dynamic contractions.