Objective  In the process of tree pruning, pole chain saw as an efficient and convenient tool effectively reduces the risk of climbing trees for forest workers. In this work, the ergonomic evaluation of typical electric pole saws in the market was carried out, and an improvement scheme with movable handle was proposed for its defects. The effectiveness of the modified scheme was proved by comparative experiments, which provided an improvement idea for the same type of tools.

  Method  The movable handle can be used to adjust the fatigue load of the tool on the arm and the whole body by changing the distance between the holding point and the center of gravity. Seventeen males were selected to perform the experiment, during which their heart ratio, surface electromyography signals of biceps brachii and palmar longus, grip distance and subjective assessment were measured during the operation of the original electric pole saw, and to select improvements based on these data.The improvement effect was evaluated by comparing the improved experimental data with that of the control group.

  Result  Before the improvement,the increase ratio of heart rate of the subjects was greater than 18%, indicating that the whole body fatigue load was too large. Besides, the normalized surface electromyographic signals of biceps brachii and palmar longus were higher than 20% and 30%, respectively, which revealed excessive local fatigue. By paired sample t test method, the increasing ratio of heart rate, the normalized surface electromyographic signals of biceps brachii and palmar longus, subjective assessment, and grip distance were significantly different before and after the improvement (P < 0.05).

  Conclusion  The overall evaluation results show that the modified electric pole chain which allows the operator to adjust the grip distance between the hands freely by the movable handle can effectively reduce the fatigue load of the arm and the whole body, and finally improve the operation comfort. Moreover, the additional cost of the modification is controlled below 100 CNY, which increases the feasibility of universal promotion.