Electrodes for electromyography were attached to 11 shoulder muscles: supraspinatus, infraspinatus, subscapularis, pectoralis

major, teres major, latissimus dorsi, rhomboid major, lower trapezius, upper trapezius, serratus anterior, and deltoid. Initially, a maximum voluntary contraction was elicited from each muscle group for later comparison. Participants then isometrically Nutlin-3 in vitro adducted their shoulder at three angles (30°, 60°, and 90° of shoulder abduction) at four loads (25%, 50%, 75%, and 100% of maximum load). Adults were eligible to participate in the study if they had no history of shoulder pain in the previous two years and had never sought treatment for BLU9931 chemical structure shoulder pain. Prior to commencement of data collection, a physical examination of the test shoulder was performed. Participants were excluded if they did not demonstrate normal range of movement and normal scapulohumeral rhythm, or if they

had any pain on isometric rotation strength tests. To establish maximum voluntary contraction in each of the 11 shoulder muscles, four Shoulder Normalisation Tests were performed. These tests have previously shown to have a high likelihood (95% chance) of generating maximum electromyographic activity in the shoulder muscles tested (Boettcher et al 2008). Each Shoulder Normalisation Test was performed three times with at least 30 seconds rest between

each repetition. The order of the tests was randomised to avoid systematic effects of fatigue. Each participant stood in an upright posture with the scapula retracted. The shoulder to be tested was positioned in the scapular plane (30° in front of the coronal plane of the body) at the shoulder abduction angle to be tested. Isometric adduction testing was performed in random order at 30°, 60°, and 90° abduction. The opposite hand rested on the opposite hip to prevent compensatory trunk movements during the adduction tests. The participant held a handle attached to a force transducera and then exerted an adduction force displayed those to the participant on an oscilloscopeb (Figure 1). Target forces, corresponding to 25%, 50%, 75%, and 100% of the participant’s maximum isometric adduction force at each of the three abduction angles (determined prior to the insertion of electrodes), were displayed on an oscilloscope. Participants were instructed to adduct the arm isometrically to match the target and were required to build up to the target force during the first second, hold it for three seconds, then release slowly over the final second. In total, 12 conditions were tested in random order, ie, contractions at 25%, 50%, 75%, and 100% of the maximum load were each performed at 30°, 60°, and 90° abduction. Two repetitions of each condition were performed.