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Jennifer N. Norman1, Kelly E. Joniak1, Ryan M. Miller1, Aaron D. Heishman1,2, Eduardo D.S. Freitas1, Samuel R. Buchanan1, Michael G. Bemben1 FACSM.1Department of Health and Exercise Science, University of Oklahoma, Norman, Oklahoma. 2Basketball Strength and Performance, University of Oklahoma, Norman, Oklahoma.

Premenopausal and postmenopausal women typically display differences in muscle mass and muscle function. However, previous research comparing the effects of menopausal status on muscle function are often influenced by different age groups, which may highlight the impact of aging rather than menopausal status on muscle function. PURPOSE: The purpose of this study was to examine whether age-matched pre-and postmenopausal women display differences in maximal voluntary isometric force (MVIC) and isotonic knee extensor (KE) muscular strength at three relative loads (20, 40, and 60% MVIC). Isotonic parameters (e.g. power[P]and velocity[V]) were selected since previous research has indicated these parameters reflect functional status and are influenced by the presence of sex hormones. METHODS: Twenty-four women (premenopausal [n=12]: 48.2 ± 4.6years164.2 ± 6.4cm, 68.4 ± 10.8kg;postmenopausal [n=12]:49.9 ±2.7years, 164.2 ± 6.0cm, 62.3 ± 11.9kg) completed three separate visits requiring an MVIC followed by isotonic testing of the KE. Isotonic testing was performed with three loads representing 20, 40, and 60% KE MVIC, with participants completing three repetitions at each load. Each repetition was separated by 30 seconds, and 60 seconds rest was provided between each testing load. Participants completed body composition testing via dual-energy x-ray absorptiometry prior to the first day of testing and statistical significance was set at p<0.05. RESULTS: No differences were observed for anthropometric measures (p≥0.156), lean body mass (p≥0.151), or KE MVIC (p=0.136). Premenopausal women displayed significantly greater peak P and peak V at 20% MVIC (p=0.038 and p= 0.013, respectively) and 40% MVIC (p=0.042 and p=0.046). Additionally, time to peak V and time to peak P were significantly faster for the premenopausal women at 20% MVIC (p=0.042 and p=0.001, respectively) and 40% MVIC (p=0.034 and p=0.006, respectively). CONCLUSIONS: Since no age differences in MVIC or lean body mass were observed, these observations suggest a potential effect for sex hormones on muscle function. Further, these results could be used to structure training programs that may help postmenopausal women maintain speed and power, thereby reducing the effects of the menopausal transition.

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