The analysis uses dimensionality reduction techniques to identify regularities in spatial, temporal or spatio-temporal patterns of multiple muscle activation. Muscle synergy analysis is increasingly used in domains such as neurosciences, robotics, rehabilitation or sport sciences to analyze and better understand motor coordination. These inter-individual differences should be investigated in the occurrence of shoulder musculoskeletal disorders. The other subjects co-contracted all shoulder muscles as a unit in both conditions. In 3/4 of subjects, lowering movements involved greater activation of a “multiple antagonists” synergy. Lifting and lowering a load were associated with similar synergy structure. Synergy #2 was more activated during lowering and explained the greater activity observed in anterior deltoid, serratus anterior and pectoralis.Conclusion Synergies’ structure was similar between lifting and lowering (Pearson’s r ≈ 0.9 for synergy #1 and 0.7–08 for synergy #2). Synergy #1 mainly activated prime movers’ muscles, while synergy #2 co-activated several antagonist muscles. Two synergies were identified in ~ 75% of subjects, and one synergy in the others. The number of synergies was the same in both tasks. 15.9 cm/s) but with similar hand paths and segment kinematics. The movements were performed faster during lifting (18.2 vs. Kinematics, EMG levels and muscle synergies, extracted using non-negative matrix factorization, were analyzed.ResultsWe found greater muscle activity level during lowering in four muscles (+ 1–2% MVC in anterior deltoid, biceps brachii, serratus anterior and pectoralis major). We tested the hypothesis that lowering a load involves different shoulder muscle coordination strategies compared to lifting a load.MethodsEMG activity of 13 muscles was recorded in 30 healthy volunteers who lifted and lowered a 6, 12 or 18 kg box between three shelves. PurposeLowering a load could be associated with abnormal shoulder and scapular motion.
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