Effects of Short-Term Hand Tractor Operation on Upper Limb Responses of Users

ABSTRACT

Objectives

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.

Methods

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.

Results

The total unweighted handle vibration acceleration is 17.45 ± 7.53 m/s². 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 (p < .05) than the bicep and deltoid. The post-task grip strength of the dominant hand was lower than its pre-task value (p < .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 (p < .10). Although, overall, the perceived discomfort ranged from none to mild discomfort.

Conclusion

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.

KEYWORDS:

• Hand tractor operation
• upper limb muscle activity
• hand grip strength
• occupation vibration

Acknowledgments

The researchers would like to express their gratitude to the farm operators of Gerona, Tarlac, Philippines that participated in the study and the staff members of RiceBIS Project for coordinating the schedules and farm plots that were used in the study.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

This work is supported by the Enhanced Creative Work and Research Grant (ECWRG) Program of the Office of the Vice President for Academic Affairs (OVPAA), University of the Philippines.