Dannecker EA, O’Connor PD, Atchison JW, Robinson ME; University of Florida and Shands Hospital, Gainesville, FL. OCONNPD@shands.ufl.edu.

PURPOSE: As part of a larger investigation, this preliminary study examined sex differences in several parameters of exercise induced muscle damage. The theorized mechanisms for sex differences are numerous, but the protective effect of estrogen on inflammation and damage has recently received attention (Clarkson and Hubal, 2001; Tiidus, 2003). SUBJECTS: The sample included 12 upper-body untrained university students (58% women). METHODS: Dominant arm girth (4 locations), elbow range of motion (ROM; resting angle and flexion angle), and arm pain were the muscle damage parameters collected immediately before and two days after participants completed a 5 RM eccentric strength test and 3 sets of 12 eccentric-biased repetitions. ANALYSES: Sex differences in total work, distance, and percentage of peak torque during the eccentric-biased repetitions were examined using independent samples t-tests. In addition, the association between these exercise variables and the change in muscle damage parameters was checked by means of Pearson correlations. Finally, 2 (sex) x 2 (time) mixed model analyses of variance were performed with girth, ROM, and pain as dependent variables. Measures of the meaningfulness of the mean differences (i.e., effect size) were also calculated. RESULTS: As expected men performed more total work during the eccentric-biased repetitions than women, t (11) = 7.81, p < .001, d = 49.22. No significant sex differences were detected for distance and percentage of 5 RM, but the effect size for the mean difference in distance was large (d = 1.11). Significant increases in pain and girth and decreases in ROM were detected, but no pattern of association between the exercise variables and the change in muscle damage parameters was noted. Interestingly, effect sizes indicated a different pattern of inflammation for females than males (η²s = .06 - .12), but these effect sizes were affected by the use of total work as a covariate. CONCLUSION: The lack of association between exercise variables and muscle damage parameters that was observed in this investigation has been reported by other investigators. Continued research to determine the exercise variable (e.g., muscle length, stiffness, tension, etc.) most predictive of primary muscle damage parameters is needed. Evidence of different patterns of inflammation between the sexes across time may support reports of the beneficial effects of sex hormones on inflammation. Additional investigations of this issue with larger sample sizes is warranted. FUNDING SOURCE: Grant 5F32 (AR08623-01) to Dr. Erin A Dannecker from the National Institute of Arthritis and Musculoskeletal and Skin Diseases and Grant 1RO1 (DE 13208-01A2) to Dr. Michael E. Robinson from the National Institute of Dental and Craniofacial Research.

Copyright 2004 by the American Physical Therapy Association

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