A method of surface myoelectric signal measurement and analysis is presented with the aim of evaluating muscle fatigue during cyclic dynamic contractions, such as those encountered in everyday sport activities and during training or kinesiological rehabilitation. During such activities subjective variability of certain biomechanical movement parameters exists. Surface myoelectric signals from three upper leg muscles (m. rectus femoris, m. vastus lateralis, m. vastus medialis) were monitored during lower leg extension and flexion exercise on commercially available training device. Simultaneously with electromyographic measurement, shaft angle of the training device as a kinematic parameter of movement was monitored, as well as the heart rate, used as a fatigue indicator of the complete subject’s organism. Comparing kinematic movement parameters, differences in performance of defined movement between subjects were noticed. A method of non-stationary signal time-frequency analysis, based on power spectra estimation using short-time Fourier transform, i. e. spectrogram, was used in the analysis of myoelectric signals recorded during dynamic contractions. As an indicator of muscle fatigue, a change in power spectrum median frequency calculated from the spectrogram has been used. According to the results of the analysis, this method provides an objective evaluation of particular muscle’s fatigue, among the agonists participating in the movement, as well as an indication of differences in dominant muscle fibre type in observed muscles. The results of the study, the developed measurement technique and the method of signal processing and analysis can be applied in muscle fatigue evaluation during cyclic dynamic contractions in various areas of human activities, as for instance during follow-up of sports training efficiency, ergonomic analysis and monitoring of therapeutic methods efficiency in kinesiological rehabilitation.