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. 2023 Sep 1;20:112. doi: 10.1186/s12984-023-01236-2

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© This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2023

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

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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