Abstract: Objective:To validate accuracy and rationality of the wavelet transform analysis of surface myoelectric signal(sMES) when muscle fatigue was monitored in the repetitive manual lifting and lowering tasks.Methods:BTE PrimusRS system and surface electromyography instrument were synchronized,40 male undergraduate students repeated twice the test of repetitive lifting and lowering capacity.The lifting frequency was 12lifts/min,wooden box(35cm×25cm×25cm) was 13kg,squat and semi-squat were undertaken by turns,and the interval was 30 minutes.sMES and the immediate discomfort self-ratings after this test were recorded.Before and after this test,subjects were instructed to pull upwards the handle at maximum effort for 6s,each set contained 3 times,and the interval was 15s.Results:The fatigue concentrated in a few parts of the body under the semi-squat,especially in the lower back,and the degree of fatigue became more apparent.The parameters detected by BTE PrimusRS system showed that squat was better than semi-squat.The instantaneous median frequency(IMDF) significantly decreased in the right paravertebral back muscles at T10,pairs of paravertebral back muscles at L3,rectus femoris and vastus lateralis under the squat.The results were similar with the right trapezius,pairs of paravertebral back muscles at L3 and medial gastrocnemius muscle under the semi-squat.Conclusion:The wavelet transform analysis technique of sMES could monitor the muscle fatigue accurately and reasonably in the repetitive manual lifting and lowering tasks.