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Activation pattern of the upper extremity muscles during dynamic push and pull tasks

Manual pushing and pulling is a common occupational task that has been associated with the development of various work-related musculoskeletal disorders, but research regarding the biomechanics of sub-maximal pushing and pulling exertions has been limited. This study was conducted to evaluate the activation pattern of upper extremity and shoulder muscles during sub-maximum dynamic pushing and pulling exertions with varying horizontal and vertical loads. Twenty young healthy female participants performed repetitive pushing exertions and pulling exertions against horizontal resistance (1 kg, 2 kg, or 3 kg) while supporting vertical hand load (0.6 kg, or 1.3 kg). Myoelectric signal of the seven upper extremity and shoulder muscles were collected during the exertions to assess the activation level of the muscles. Results found that the anterior deltoid muscle was the main mover of the sub-maximal pushing and the elbow flexors were the main muscles of the sub-maximal pulling exertions. The analysis on the effect sizes of two loads showed that the activation of the muscles near the shoulder joint were more sensitive to the horizontal load, while the forearm muscles and the elbow flexors were more sensitive to the vertical load. Study findings showed how muscles of the upper extremity and the shoulder would respond differently to the changes of the vertical and horizontal hand loads during sub-maximal pushing and pulling exertions. Results could be used to understand the mechanism of injury of low-to-moderate exertion pushing and pulling tasks such as hand sawing and floor vacuuming.