Department of Industrial Engineering, College of Engineering and Agro-Industrial Technology, University of the Philippines Los Baños, Laguna, Philippines.
J Agromedicine. 2024 Jul;29(3):415-425. doi: 10.1080/1059924X.2024.2338844. Epub 2024 Apr 9.
Continuous exposure to hand-arm vibration integrated with poor posture and forceful movements are known causes of musculoskeletal disorders (MSD). In most related studies, force and vibration levels in experimental research is controlled. This study aims to determine how actual hand tractor field operation can affect the upper limb of users. It intends to characterize upper limb muscle activation applied during actual hand tractor usage. Lastly, it determines the immediate impacts on hand strength and perceived upper limb discomfort after the operation.
We recruited 15 farm operators with a mean working experience of 20.1 ± 12.2 years. They were asked to operate a hand tractor on paddy fields for at most 8 minutes. Handle vibration was measured using a tri-axial accelerometer. The total unweighted vibration acceleration was computed and used to represent the handle vibration magnitude. Muscle activation was measured using surface electromyography (sEMG). Six sEMG sensors were attached to the dominant and non-dominant side of the extensor carpi radialis (ECR), bicep, and deltoid. Pre- and post-task hand strength and subjective discomfort rating were also taken.
The total unweighted handle vibration acceleration is 17.45 ± 7.53 m/s. This exceeds the allowable safe value. Meanwhile, the percentage of maximum voluntary contraction (% MVC) of the muscles ranged from 6% to 14% with the ECR having a significantly higher activation ( < .05) than the bicep and deltoid. The post-task grip strength of the dominant hand was lower than its pre-task value ( < .01) while that of the non-dominant side did not vary significantly. There is a modest trend of higher hand discomfort of the non-dominant side on post-task than pre-task rating ( < .10). Although, overall, the perceived discomfort ranged from none to mild discomfort.
In conclusion, the study showed an indication that the effects of vibration on humans are evident even at mild muscle exertion, with the exertion predominantly concentrated on the distal arm area clearly affecting grip strength and hand discomfort. In such cases, future recommendations can revolve around the improvement of the hand tractor handle grip to impose grip comfort and ease.
已知手臂和手部持续受到振动且姿势不佳、用力过度是导致肌肉骨骼疾病（MSD）的原因。在大多数相关研究中，实验研究中的力和振动水平是可控的。本研究旨在确定实际手扶拖拉机作业如何影响使用者的上肢。它旨在描述实际使用手扶拖拉机时所施加的上肢肌肉激活情况。最后，确定操作后对手部力量和上肢不适感的即时影响。
我们招募了 15 名平均工作经验为 20.1±12.2 年的农场操作员。要求他们在稻田里操作手扶拖拉机最多 8 分钟。使用三轴加速度计测量手柄振动。计算总非加权振动加速度并用于表示手柄振动幅度。使用表面肌电图（sEMG）测量肌肉激活。在优势侧和非优势侧的伸腕肌（ECR）、二头肌和三角肌上分别贴上 6 个 sEMG 传感器。还进行了任务前后手部力量和主观不适评分。
总非加权手柄振动加速度为 17.45±7.53m/s，超过允许的安全值。同时，肌肉的最大自主收缩百分比（% MVC）范围为 6%至 14%，其中 ECR 的激活明显高于二头肌和三角肌（ < .05）。优势手的任务后握力低于任务前（ < .01），而非优势手的握力没有显著变化。任务后非优势手的手部不适评分较任务前有升高的趋势（ < .10）。尽管总体上的不适感从无到轻度不适不等。
综上所述，研究表明，即使在轻度肌肉用力的情况下，振动对人体的影响也是明显的，主要集中在手臂远端区域的用力明显影响握力和手部不适。在这种情况下，未来的建议可以围绕改善手扶拖拉机手柄的握持舒适度来展开。
