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To investigate the effects of concentric or eccentric abduction strength training on supraspinatus fiber bundle architecture and strength.

A pre–post single-subject design.

Thirteen participants were randomized to concentric (n = 6) or eccentric (n = 7) training groups. Participants completed an eight week shoulder abduction training program in the scapular plane using an isokinetic dynamometer. Resistance training, requiring maximal effort on contraction, consisted of 4 sets of 8 reps at 60°/s in weeks 1–4, and 6 sets of 6 reps at 60°/s in weeks 5–8 with a frequency of 3×/week. Primary outcome measures included fiber bundle length, pennation angle, and muscle thickness of supraspinatus and these were quantified using ultrasound. Secondary outcome measures included isometric, eccentric and concentric abduction strength and these were evaluated using the isokinetic dynamometer …