Isokinetic evaluation of shoulder internal and external rotators concentric strength and endurance in baseball players: Variations from pre-pubescence to adulthood

This study compared the strength and endurance of shoulder internal rotators (IR) and external rotators (ER) among baseball pitchers of four age levels. Eighty baseball pitchers aged 10-23 years participated this study. Strength was assessed by the average peak torque of the middle 3 out of 5 repetitions. Endurance was assessed by thirty concentric internal and external contractions. Percentage of strength loss, initial and final torque ratio were used to assess endurance ability. The results showed that IR strength was greater than the ERs for all groups. The ER/IR ratio ranged 0.71-0.77. In endurance assessment, the players were found to have 70% strength loss in the IRs. Adolescent and pre-pubescent players had larger p < 0.05) strength loss in the ERs. Compared with adult pitchers, adolescent and pre-pubescent baseball pitchers had relatively weaker shoulder ERs especially after high repetition muscle contraction. In order to prevent shoulder injury in adolescent and pre-adolescent baseball throwers, muscle endurance in ER should be emphasized.