工作頻率對於肌肉骨骼系統之影響

Pace of Work and Its Effects on the Musculoskeletal System

目標：高頻率的重複動作是造成上肢工作性傷病的主要原因之一，然而許多傳統產業、物流業、餐飲業等工作，仍需要高頻率的手部重複動作來完成。因此，建立一套適當的重複動作頻率，可以減少工作傷害及提高生產力。本研究旨在以客觀的測量分析，找出個人在重複動作時最適當的頻率。方法：30 位自願受試者（男性18 人；女性12 人） 模擬舀水、倒水的上肢重覆動作。以MicroFET4dynamometer 測量在不同的頻率及工作負荷量下，重複動作後之最大意志收縮手握力值 (Maximum Volitional Contraction, MVC) 做為上肢功能指標。同時以SPSS12.0 統計軟體分析資料，採用重複量數分析、成對樣本t-test 檢定。結果：男性在實驗前之握力值顯著大於女性，兩者皆在工作量持續增加時，握力顯著遞減(p<0.01)。但是，頻率對兩性有不同的影響，在20cycles/minute 及25 cycles/minute的頻率下，女性在較快速的頻率時，握力值顯著大於在較慢頻率時的握力值(p<0.05)；男性則是在頻率增加至35 cycles/minute 才顯現出此現象。結論：相對於直覺的預期在疲勞或壓力下握力值應該減低，本研究卻發現個人在重覆動作的速率已達“臨界點”時，為了因應工作速率的負荷而促使動用心血管的儲備量，故呈現出握力值增加的現象。採用MicroFET4 dynamometer 測量握力值，確為較簡易實用的方法，能快速評估個人在重覆動作時的適當頻率。此項研究結果可應用於輔助人因工程檢核表（例如：快速上肢測量評估），以提供相關業者制定適合的工作頻率，以預防工作性肌肉骨骼傷病。

Objective: Excessive pace is a major cause of upper limb work-related musculoskeletal disorders. To maximize output while minimizing disability, it is useful to establish an acceptable pace of industrial workers at a given task. Our aim is to provide objective evidence to assist those searching of the most suitable pacing of repetitive work. Methods: 30 volunteers performed a repetitive task of scooping and pouring at different duration and pacing speeds. As an index of upper limb function, grip strength (Maximal Volitional contraction, MVC), was measured by Micro FETE4 dynamometer. The statistical data were analyzed by repeated measure design and paired t-test, using SPSS 12.0 software. Results: Duration of task caused decline in grip strength (p<0.01), as anticipated. Increasing pace, however, produced unexpected results that seemed paradoxical. In females, when pace was increased to a critical level (25 cycles/minute), the grip strength was found to show a transient increase. While males did not show this at the pace noted for females, they did show a similar effect when pace was further increased (35 cycles/minute). Conclusions: These results are counter-intuitive: one would expect grip strength to decline as one became tired or stressed. We suggest that this transient increase in grip strength is a mark of “critical threshold” pace, and approaching strain, indicating reflex activating of extra cardiovascular reserves in response to a taxing pace. Measurements of grip strength by dynamometer are simple and useful complement to ergonomic checklist, such as Rapid Upper Limb Assessment (RULA), in helping those responsible for industrial health and safety when planning optimal working pace.