The effects of posture, duration, and force on pinching frequency

Abstract A laboratory experiment was conducted utilizing the psychophysical approach to establish the maximum acceptable frequency (MAF) for a pinching task. The type of pinch used was the lateral pinch. The psychophysically adjusted pinching frequency was determined by the method of adjustment for each of 18 combinations of wrist posture, force, and duration. Twelve healthy males served as subjects. The results indicated that the MAF was significantly reduced as the angle of wrist flexion, pinching force, and task duration increased. This decrease was exponential, not linear. These results were supported by the EMG analysis and the ratings of perceived exertion and body discomfort. The upper limit for mean intensity in this study was 12.7%. If the criteria for acceptability can be defined in terms of the absence of EMG signs of fatigue and low subjective ratings, then the tasks involving 2 3 maximum wrist flexion, 50% MVC, and/or 7 second task duration were not acceptable. These results are similar to those found in other studies involving different types of hand/wrist work. Relevance to industry The results of this study will be useful in determining acceptable or alternative job designs for many hand/wrist tasks which involve pinching.