Isokinetic evaluation of shoulder internal and external rotators
concentric strength and endurance in baseball players: Variations from
pre-pubescence to adulthood
Affiliations: [a] Department of Orthopaedics and Traumatology, Taipei
Veterans General Hospital, Department of Surgery, National Yang Ming
University, Taiwan | [b] Graduate Institute of Rehabilitation Science and
Technology, National Yang Ming University, Taiwan | [c] Department of Physical Education, National Yang Ming
Univeristy, Taiwan | [d] Institute and Faculty of Physical Therapy, National
Yang Ming University, Taiwan | [e] Graduate Institute of Physical Education, National
College of Physical Education and Sports, Taoyun, Taiwan
Note: [] Address for correspondence: Dr. Shun-Hwa Wei, Graduate Institute
of Rehabilitation Science and Technology, National Yang Ming University, 115
Li-Noon St., Shih-Pai, Taipei, Taiwan. Tel.: +886 2 28267190; Fax: +886 2
28201841; E-mail: [email protected]
Abstract: 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.
