Young and older adult females show increased muscle compensation compared to males while moving an external load for...

Rotator cuff tears (RCT) are common. Prior work studied effects of RCT severity, load, and task on functional performance, but no work has examined the combined effect of factors or age- and sex-based effects, which was the objective of this study. Models representing young/older adult males/females with varying RCT severity were used. Seven external loads were applied to the hand during 3 functional tasks. Multiple 2-way ANOVAs and exploratory mixed effects model were used to determine muscle force differences between RCT severity, external load, sex, age, and task. Root mean squared error (RMSE) was used to quantify hand deviation. The deltoid, pectoralis major, infraspinatus, and teres minor muscles increased force for interactions of RCT severity, external load, age, sex, and task and the following main effects: RCT severity (all p < 0.0043), external load (all p < 0.0001), female sex (all p < 0.0001), age (all p < 0.0214), and multi-planar tasks (all p < 0.0001). Larger force contributions occurred for female/older adults with increased RCT severity/external load. Greatest hand deviation occurred for massive tear severity, 66.7 N load for all model permutations (all RMSE > 0.0077 m), with greater deviation for multi-planar vs planar tasks. Study outcomes aid in development of sex, age, and RCT severity specific rehabilitation that incorporates multi-planar movement.