Examining upper extremity and trunk muscle activation in novice participants during a simulated tree planting task

Colwell, Emily Marguerite (2020) Examining upper extremity and trunk muscle activation in novice participants during a simulated tree planting task. Masters thesis, Memorial University of Newfoundland.

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Abstract

Manual reforestation is common in Canada and has a high rate of injury, many of which appear to go unreported, and approximately 80% of tree planting injuries are classified as “chronic”. Previous research has suggested muscle activation levels as underlying factors in the development of upper extremity and back pain. The purpose of this study was to examine surface electromyography (sEMG) in novice participants during simulated tree planting tasks to describe the muscle activation in the trunk and upper extremity during tree planting. Twenty participants (10 female, 10 male; age: 23.8 ± 4.18; body mass index [BMI]: 25.3 ± 4.16 kg/m²) completed an average of 25 ± 3 planting attempts to achieve 20 trials of acceptable quality plants (min: 21, max: 32). Six muscle groups were selected for sEMG recording: wrist extensors, wrist flexors, upper trapezius, erector spinae, rectus abdominus, and external obliques. All data from the rectus abdominus and external obliques were removed from analysis due to poor quality. Findings revealed that muscle activity in the shovel-side musculature was typically greater than in the draw-side in the earlier phases of planting, while activity in the draw-side musculature was typically greater than that in the shovel-side in the later phases of planting. Results of amplitude probability distribution function (APDF) analysis indicated that persistent low-level static exertions (10th percentile APDF of greater than 2% maximum voluntary contraction [MVC]) were observed in the shovel-side wrist flexors and extensors and erector spinae, as well as in the draw-side wrist extensors and upper trapezius. Although peak activation was not explicitly quantified, the linear envelope data showed maximum activations of approximately 25% MVC in all shovel-side musculature and in the draw-side forearm musculature. Persistent low-level muscle activation, high peak exertions, and high impact forces are ergonomic risk factors that may contribute to development of pain and musculoskeletal disorders (MSDs). Thus, the study findings support the existing theory that persistent muscle activation plays a role in the high rate of injury present in this population.

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