We have investigated the electromyographic manifestations of fatigue on the Biceps Brachii in prolonged isometric and dynamic contractions by using two spectral analyses (Fourier transform (FT) and continuous wavelet transform (CWT)) as references and a novel approach cyclostationarity analysis. The isometric fatigue test shows no deviations from what is found in the literature (increase in energy (En) and decrease in mean frequency (MF)), while the dynamic fatigue test shows a slight increase in En and no change in MF for both spectral estimation techniques. In addition, the cyclostationarity increases with the fatigue and it could provide a new index of the fatigue during cyclostationary dynamic movements.