Shoulder load during wheelchair-related activities of daily life

Manual wheelchair users experience significant upper extremity strain, leading to a high prevalence of shoulder pain. Identifying modifiable risk factors for shoulder complaints is crucial for developing effective interventions. Consequently, it's important to quantify shoulder load (magnitude, frequency and duration) experienced by manual wheelchair users throughout the day. This study aims to quantify the magnitude of shoulder load during various daily activities, including wheelchair propulsion at different speeds and inclines, ascending and descending ramps, weight relief lift, material handling and desk work. Ten able-bodied participants performed these activities while their upper extremity kinematics and exerted forces were measured. The analysis focused on glenohumeral contact force and rotator cuff muscle forces using the Delft Shoulder and Elbow Model. Highest mean glenohumeral contact forces were found during weight relief lift (1363 ± 1204 N), followed by descending a ramp (997 ± 1043 N) and fast propulsion (802 ± 742 N). The supraspinatus muscle generated the greatest force during weight relief lift (327 ± 490 N) and fast propulsion (184 ± 205 N). These findings provide a first reference for estimating joint load in daily activities. By combining these data with the individual activity frequency and duration, personalized shoulder load exposure can be assessed, informing the development of targeted interventions to reduce shoulder pain in manual wheelchair users.