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The purpose of the current study was to determine shoulder internal rotator muscles' reflex latencies (SLR) under variable conditions in 20 healthy, specifically trained male participants. Sets of different external shoulder rotation stretches were applied via an isokinetic dynamometer. SLR latencies were determined from sEMG readings as the time from external shoulder rotation stretches application to onset of muscle activity. The amount of muscular response to the perturbation was evaluated via a peak-to-peak analysis. SLR latencies and amplitudes of the pectoral muscle and the anterior deltoid were affected by the investigated muscle and the level of pre-innervation torque. Our results indicated faster muscular stretch response than reported in previous studies which can be attributed to training induced adaptions of the shoulder muscles and capsule.