• Hiroki Miyamoto, Kota Watanabe, Atsushi Teramoto, Naoya Iida, Tatsuya Taniguchi, Kento Hirota, Keisuke Negishi, and Mineko Fujimiya.
• Graduate School of Health Sciences, Sapporo Medical University, Sapporo, Japan.. Electronic address: pt_miyamotohiroki@yahoo.co.jp.
• Clin Biomech (Bristol, Avon). 2020 Dec 1; 80: 105160.

BackgroundThe shoulder is a uniquely complex large joint. Effective and safe physical therapy efforts towards rehabilitating injured and repaired shoulders requires a thorough understanding of shoulder mechanics from both generalized and very specific perspectives. Numerous biomechanical studies have been published on the shoulder. None of the studies, to our knowledge, considered the strain of the deep layers of the supraspinatus tendon for scapular plane elevation.MethodsTen unilateral fresh-frozen human cadaveric specimens were used for the study. Scapular plane angles ranging from -10 to 30 degrees were evaluated for tensile loads, ranging from 0 to 120 Newtons, exerted on the supraspinatus tendon. Strain measurements that specifically targeted the deep layer of the supraspinatus tendon during tensile loading were recorded.FindingsStrains recorded in the supraspinatus deep layer while increasing tendon force of the supraspinatus were significant for isometric gleno-humeral elevation of 30° and 20°. The response of strain to tendon force was less pronounced for 10° or less of gleno-humeral elevation.InterpretationWhen performing isometric shoulder exercise regimens, rotator cuff forces and both surface and deep tendon strain, relative to scapular positioning, are relevant and should be considered.Copyright © 2020 Elsevier Ltd. All rights reserved.

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