title: Electromyographic assessment of muscle fatigue in massive rotator cuff tear.
abstract: Shoulder muscle fatigue has not been assessed in massive rotator cuff tear (MRCT). This study used EMG to measure fatigability of 13 shoulder muscles in 14 healthy controls and 11 patients with MRCT. A hand grip protocol was applied to minimise artifacts due to pain experience during measurement. The fatigue index (median frequency slope) was significantly non-zero (negative) for anterior, middle, and posterior parts of deltoid, supraspinatus and subscapularis muscles in the controls, and for anterior, middle, and posterior parts of deltoid, and pectoralis major in patients (p ≤ 0.001). Fatigue was significantly greater in patients compared to the controls for anterior and middle parts of deltoid and pectoralis major (p ≤ 0.001). A submaximal grip task provided a feasible way to assess shoulder muscle fatigue in MRCT patients, however with some limitations. The results suggest increased activation of deltoid is required to compensate for lost supraspinatus abduction torque. Increased pectoralis major fatigue in patients (adduction torque) likely reflected strategy to stabilise the humeral head against superior subluxing force of the deltoid. Considering physiotherapy as a primary or adjunct intervention for the management of MRCT, the findings of this study generate a base for future clinical studies aiming at the development of evidence-based protocols.
authors.affiliation: Musculoskeletal Science Research Group, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
authors.forename: D H
authors.initials: DH
authors.lastname: Hawkes
authors.affiliation: School of Health Sciences (Sport and Exercise Science), Liverpool Hope University, Liverpool, UK. Electronic address: alizado@hope.ac.uk.
authors.forename: O
authors.initials: O
authors.lastname: Alizadehkhaiyat
authors.affiliation: Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, UK.
authors.forename: G J
authors.initials: GJ
authors.lastname: Kemp
authors.affiliation: Department of Medical Physics and Clinical Engineering, Royal Liverpool University Hospital, Liverpool, UK; Department of Physics, University of Liverpool, Liverpool, UK.
authors.forename: A C
authors.initials: AC
authors.lastname: Fisher
authors.affiliation: Musculoskeletal Science Research Group, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
authors.forename: M M
authors.initials: MM
authors.lastname: Roebuck
authors.affiliation: Musculoskeletal Science Research Group, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
authors.forename: S P
authors.initials: SP
authors.lastname: Frostick
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D004576:Electromyography; D018737:Hand Strength; D006801:Humans; D008875:Middle Aged; D018763:Muscle Fatigue; D000070636:Rotator Cuff Injuries
keywords: EMG; Electromyography; Massive rotator cuff tear; Muscle fatigue; Painful shoulder; Shoulder