Electromyography Signal Analysis of Knee Flexor and Extensor Muscles in Potential Knee Musculoskeletal Disorders during Roofing

Awkward and extreme kneeling postures required during shingle installation on sloped rooftops generates large muscular tension on lower extremities of residential roofers. This study assessed the effects of kneeling posture and roof slope on the peak activations of knee flexor (biceps femoris and semitendinosus) and extensor (rectus femoris, vastus lateralis, and vastus medialis) muscles that are potential risk indicators of knee musculoskeletal disorders (MSD) in shingle installation. Using surface electromyography (EMG), the authors collected maximum normalized EMG signals from the above-mentioned muscles of seven subjects who mimicked a shingle installation task with kneeling on a slope-configurable wooden platform. The results suggested a significant association of the roof slope, kneeling posture, and their interaction with the peak muscle activation. Except for the vastus medialis muscle of the right knee, significant increase in the peak normalized EMG was observed for all flexor and extensor muscles during shingle installation on the sloped roof surface. Significant interaction between the slope and posture was observed for the flexor muscles of the right knee and vastus medialis muscle of the left knee. Therefore, the large muscle activations during kneeling in shingle installation on highpitched rooftops should be given particular attention as it might lead to development of the knee MSD among residential roofers.