Each pair of electrodes was aligned parallel to the line of underlying muscle fibres. Electromyographic data were sampled at 1000 Hz. The signals were amplified and digitisedc. A bandpass filter (20–450 Hz) was used. The root mean square was

calculated from the raw data using a moving window of 50 msec and was converted MK0683 to ASCII files for analysis. For normalisation, 5 sec of reference contraction data were recorded while the participant performed three trials of maximal voluntary isometric contraction in the manual muscle testing position for each muscle (Kendall et al 1993). To ensure maximal effort, verbal encouragement was given. To minimise compensation during data collection, subjects were encouraged to maintain the testing position (Boettcher et al 2008). The middle 3 sec of the 5-sec contraction were used for data analysis. The initial 1 sec was excluded to ensure maximal amplitude had been reached, and the final 1 sec was discarded to avoid possible fatigue from sustained maximal muscle contraction (Soderberg and Knutson, 2000, Dankaerts et al 2004, Tucker et al 2010). A 3-min rest period was provided between trials. The mean root mean square of the three trials was calculated for each muscle. The electromyographic signals collected during each angle of shoulder flexion were expressed as a percentage

of the calculated root mean the square of maximal voluntary isometric contraction. The secondary measure in the study was displacement of the acromion in the KPT-330 order frontal and sagittal planes. A reflective marker 14 mm in diameter was placed on the skin at the midpoint of the acromion to measure its displacement in the frontal and sagittal planes during shoulder flexion (Figure 4). The reflective markerd was not used for visual feedback, but was used

for measuring the displacement of acromion. Two video cameras were placed 1.5 m from the shoulder joint; one was located behind the subject to capture the superior and inferior displacement of the marker in the frontal plane, and the other was placed to the side of the subject to capture the anterior and posterior displacement of the marker in the sagittal plane. Two 30-cm-long wooden rods attached to the side and back of a wooden chair were used as reference points to calibrate the motion analysis systeme in the frontal and sagittal planes (Figure 5). Video files captured during the shoulder flexion test were used to calculate the displacement of the marker. The distance of the acromion movement was measured from the starting position to the end of the predetermined shoulder flexion position in cm by the video motion analysis system software (Figure 5). For each combination of flexion angle and feedback condition, the average of the three trials was calculated for the data analysis.