Concentric and eccentric muscle fatigue of the shoulder rotators.

Previous research has demonstrated fatigue resistance for eccentric compared with concentric muscle contractions in the lower extremity. The purpose of this study was to determine if eccentric fatigue resistance was also evident in the internal and external rotators of the shoulder. Ten subjects performed three sets of 32 maximum isokinetic contractions in shoulder internal and external rotation at 120°/s.One arm performed eccentric contractions and the contralateral arm performed concentric contractions. Subjects were also tested for isometric strength prior to and immediately following the isokinetic contractions. Percent change in isokinetic torque (first five repetitions versus last five for each set) and isometric torque was compared between the arms performing eccentric and concentric contractions. Fatigue with isokinetic contractions was not different between eccentric and concentric internal rotation (25% vs. 26%, p=0.76) and external rotation (24% vs. 32%, p = 0.11). Similarly, fatigue with isometric contractions was not different between eccentric and concentric internal rotation (11% vs. 5%. p=0.33) and external rotation (15% vs. 7%, p=0.07). These results indicate that unlike previously described fatigue resistance for eccentric muscle contractions in the quadriceps, dorsiflexors and plantarflexors, fatigue was not different between eccentric and concentric muscle contractions of the internal and external rotators of the shoulder.