Strength Decrease, Perceived Physical Exertion and Endurance Time for Backpacking Tasks.

Kai Way Li,Ching Chung Chen,Jenn Chun Chu

doi:10.3390/ijerph16071296

Abstract

Manual material handling (MMH) tasks create a burden for workers which could result in musculoskeletal injuries. Assessments of the decrease of muscular strength and the maximum endurance time (MET) for MMH tasks are essential in studying the ergonomic risk of MMH tasks. A backpacking experiment was conducted for measuring the MET for MMH tasks. Human participants carried a load on their back and walked on a treadmill under various load, walking speed, and ramp angle conditions until they coud no longer do so. It was found that the participants were able to walk for approximately 15 min to two hours before they needed to have a pause. Their back and leg strengths declined moderately due to performing the tasks. These tasks resulted in an increase in heart rate and elevated perceived physical exertion. The rating of perceived exertion (RPE)/heart rate ratio in our backpacking tasks was 31% higher than that in the literature, implying the calibration of the RPE may be required for such tasks. A MET model incorporating the fMVC_back, body weight, walking speed, and ramp angle was established. This model may be used to determine the work/rest allowance for backpacking tasks under conditions similar to this study.

Highlights

Body pain and discomfort due to undesirable conditions such as overexertion and unnatural postures are common at work
Our results indicated that the heart rate of the participants increased 9.1% to 62.7% depending on the weight carried, walking speed, and ramp angle
Even though the results indicated that walking with load carriage resulted in increased heart rate and elevated rating of perceived exertion (RPE) ratings, the Pearson’s correlation coefficient between our RPE and HRa was only 0.3

Summary

Introduction

Body pain and discomfort due to undesirable conditions such as overexertion and unnatural postures are common at work. Based on labor insurance claim data, reported injuries in the neck, shoulder, and upper extremity of workers in Taiwan increased 5.2 times in a twelve-year period (2001–2013), while lower back injuries increased 1.7 times [1]. These musculoskeletal disorders have resulted in a huge burden to both workers and the society. Manual material handling (MMH) tasks are major contributors of musculoskeletal injuries in workplaces [3,4,5]. Determining the physical capability for workers is essential to the design of MMH tasks such as lifting, pushing, pulling, and carrying [6,7]. Muscular strength decreases after the muscles have contracted for a period of time, resulting in the onset of muscular fatigue

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Methods

Results

Discussion

Conclusion