Muscle activity of the rotator cuff and shoulder girdle musculature during common rehabilitation exercises

This project will explore EMG activation of rotator cuff and shoulder girdle musculature, in healthy participants during rehabilitation exercises commonly prescribed for patients with massive rotator cuff tears, and early stage post rotator cuff surgery. Based on the data we observe, we will look to develop a rehabilitation protocol for patients with massive rotator cuff tears, and post shoulder replacement. The information we gather from this study will provide information for postoperative regimes for other surgeries such as rotator cuff repair and subacromial decompression. The implications from these studies will advance the clinical knowledge and practical application of exercise rehabilitation for patients with rotator cuff disease to enhance outcomes and prevent recurrence of symptoms. Electromyographic data will be collected simultaneously from seven shoulder muscles using a combination of surface and intramuscular fine-wire electrodes. Pre-gelled and self-adhering silver/silver-chloride bipolar dual surface electrodes will be used to measure the muscle activity of the following muscles on the participant’s right side: upper trapezius, anterior deltoid, middle deltoid and posterior deltoid. The surface electrodes are to be placed on the target muscles over the belly of the muscle in line with the direction of the muscle fibres with an inter-electrode distance of approximately 20 mm. Prior to application of the surface electrodes, the skin will be cleansed and shaved (if required). Intramuscular electrodes will be used for muscles that underlie more superficial muscles (supraspinatus, subscapularis), or for muscles that shift markedly with respect to the overlying soft tissue during shoulder movement (infraspinatus). A medically trained investigator (RP) will insert all intramuscular fine wire electrodes will via a sterile 30mm, 27-gauge hypodermic needle with a pair of 0.051 mm, insulated, bent end Teflon coated stainless steel wires and 200mm tail with 5mm bare-wire terminations (Chalgren Enterprises, USA). The insertion site will be prepared using aseptic technique, via a chlorohexidine solution. Depth of the insertion will be determined using ultrasound and confirmed by visualisation of the EMG signal during maximal voluntary isometric contraction (MVIC). Surface EMG electrode placement will be attained initially through surface palpation and isometric contraction, and confirmed through visualisation of the EMG signal during MVIC (MYON m320 Telemyo system sampling at 2000Hz) via manual muscle testing. Two trials of 5-second MVICs will be performed, and will represent 100% EMG activity to be used as a standardised, within-subject reference for the data collected during the rehabilitation exercises. Verbal encouragement will be given during all trials. Electrodes will remain in place until the completion of the testing session. Passive, active and resisted movements will be performed to determine participant comfort and quality of EMG data. Muscle activation magnitude will be captured with VICON NEXUS software and post-processing will be filtered/normalised in MATLAB software (The Mathworks, Natick, MS, USA). An additional surface electrode will be placed over the clavicle to serve as a reference electrode for all surface muscles and a large ground electrode was used as a reference electrode for all intramuscular electrodes. The testing protocols will be conducted in the presence of one or more of the investigators, who are qualified Accredited Exercise Physiologists, to ensure correct body positioning and exercise technique, without excess movements during data collection. The session will last approximately 2 hours, and will require participants to undertake 11 shoulder rehabilitation exercises representing typical active ROM (AROM), active-assisted ROM (AAROM) and resistance exercises employed in clinical practice for rotator cuff disease. AAROM exercises will include: 1) shoulder elevation using a rope and pulley and 2) shoulder elevation using a broomstick, 3) wall slide exercise for elevation, 4) forward bow exercise, 5) external rotation using a broomstick both standing upright and seated, 6) the shoulder "pendulum" ROM exercise and 7) “Rock the Baby” gravity-eliminated pendulum exercise. Active exercises will include: 8) standing external humeral rotation, 9) side-lying external humeral rotation, 10) shoulder abduction, and 11) shoulder flexion. Each participant will perform 10 repetitions of each exercise at a standardised tempo matching the beat of a metronome set to 60 beats per min (2 s per concentric and 2 s per eccentric contraction). The order of exercises and loadings will be block randomised for each participant, and each set of exercise will be initiated every 2 min. Immediately after each set of exercise, the Borg CR10 scale, which has anchor points of 0 = “no exertion”, through to 10 = “extreme exertion”, will be used to rate perceived loading of the respective muscle groups during the exercise and will be carefully explained to each individual prior to testing.