The purpose of this study was to assess the effects of a 5-week shoulder-specific strength training program that emphasized the external rotators, on the total work capacity and peak torque generation of the internal and external rotator muscles, with the assumption that a low eccentric external / concentric internal total work ratio (<1.0) is correlated to an increased risk for shoulder injuries in activities involving overhead motions. This studied employed a 2 group (6 subjects each) pre-test / post-test design. Subjects were collegiate women tennis players during preseason. An experimental group participated in a 5 week, 4 times a week, strength training program. Effects of the strength training program were evaluated by comparing pre- and post-assessment data of 20 maximal eccentric external / concentric internal contractions on a Kin-Com isokinetic dynamometer. Paired t tests (Significance level = 0.05) were used to compare mean differences between pre- and post-test data for the experimental and the control group and independent t tests (Significance level = 0.05) were used to compare mean differences of changes by the experimental versus the control group of the following: Range of motion, concentric internal and eccentric external total work as well as eccentric external / concentric internal total work ratio, and the difference between the last five to the first five eccentric external / concentric internal total work ratios as an indicator for muscular fatigue. All p-values reported in this study were one-tailed values. Muscle imbalance (n = 3), relative muscle weakness (n = 9) and impaired mobility (n = 8) were observed at pre-assessment. The shoulder strength training program increased concentric internal total work (p = .077), as well as eccentric external total (p = .017) work and mean peak force performed by the experimental group (p < .05). This resulted in an increase in the eccentric external / concentric internal total work ratio (p = .077), without any significant changes by the control group. No differential fatigue of the external versus the internal rotator muscles was discernable. Neither internal nor external range of motion was significantly altered at post-assessment for either of the 2 groups. This study indicated that muscular adaptations to the game of tennis do occur at this level of play and should be opposed through a properly structured shoulder resistance program .