Local muscular fatigue is an important aspect of ergonomic studies. Spectral analysis of electromyographic (EMG) signals may be applied to provide a quantitative measure of the extent of muscular fatigue. The present study was aimed at methodological development of practical and reliable field studies for the shoulder region, EMG signals were recorded during short test contractions performed at regular intervals during work and at rest. Signal analysis was performed using the zero-crossing method. The results show that the zero-crossing method gives results which are as relevant as the MPF-method. The test contraction concept in conjunction with the zero-crossing technique is called Frequency Analysis of Test Contractions (FTC). An evaluation experiment on ten subjects at rest yielded the intrinsic standard deviation of the method and also revealed lateral covariation of the trapezius and infraspinatus muscles.