Fig. 5

Changes in the composition of muscle synergies during six weeks of training. The mean and SD of muscle weights, superimposed on the distribution of the muscle weights of participants (n = 10), per each of five synergies identified in the assessment session at Weeks 0, 2, 4, and 6. For each muscle, the weight distribution was displayed in descending order. The recorded 12 muscles included brachioradialis (BRD), biceps brachii (medial head; BI), triceps brachii (long and lateral heads; TRIlong and TRIlat), deltoids (anterior, middle, and posterior fibers; AD, MD, and PD), pectoralis major (clavicular fibers; PECT), trapezius (upper, middle, and lower fibers; UpTrp, MidTrp, and LowTrp), and infraspinatus (InfSp). A, Five muscle synergies, identified when forces were generated isometrically and habitually (not using practiced motor skills; “Habitual” condition), included (1) elbow flexor (E Flex; BRD, BI, and PECT), (2) elbow extensor (E Ext; TRIlong and TRIlat), (3) shoulder adductor/flexor (S Add/Flex; AD, MD, PECT, and UpTrp), (4) shoulder abductor/extensor (S Abd/Ext; MD, PD, and TRIlong), and (5) scapula retractor (Sc Ret; MidTrp, LowTrp, and InfSp). B, Five muscle synergies, identified when forces were generated isometrically using practiced motor skills (“As-Trained” condition). A newly acquired muscle synergy set emerged from Week 2 included (1) a combination of BRD and S Add/Flex (BRD-S Add/Flex), (2) BI dominant E Flex with minor PECT (BI-E Flex), (3) E Ext, (4) S Abd/Ext, and (5) Sc Ret