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Serum creatine kinase activity after isometric exercise in premenopausal and postmenopausal women.

The study was designed to examine the response of women of different ages to exercise-induced muscle damage. Twenty-four women were placed into 3 groups: a postmenopausal group (POST) of 6 women aged 52.8 (2.1) years [mean (SD)] who were at least 2 years without menses; a premenopausal group (PRE) of 10 women aged 43.6 (2.2) years with regular menstrual cycles of 27 (2) days; and a young (YNG) group of 8 women aged 24.6 (3.5) years with regular cycles of 31 (4) days. Serum 17 beta-estradiol measures were taken to confirm menopausal status. Three-month diaries were used to determine regular cycles. Subjects performed 40 maximal isometric knee extensions with a work:rest ratio of 10:20 seconds. Serum creatine kinase activity (CK), muscle soreness (MS), and maximal isometric strength (MVC) were assessed 24 hours prior to, immediately prior to, and 6, 24, 48, and 72 hours after exercise. Subjects experienced significant (p less than .01) increases in CK and MS, and significant decrements in MVC, with peak changes at 24 or 48 hours. Thus, isometric exercise caused slight muscle damage and muscle weakness. No significant differences among the groups were found for any measure (p greater than .05). Thus, estrogen does not seem to serve as a factor in protecting the muscle from damage due to moderate isometric exercise.