Diurnal variation, response to eccentric exercise, and association of inflammatory mediators with muscle damage variables.
This investigation determined whether inflammatory mediators 1) have diurnal variations, 2) respond to high-force eccentric exercise, and 3) associate with markers of muscle damage after high-force eccentric exercise. College-aged men and women (n = 51) completed exercise (3 x 15 maximal eccentric elbow flexor actions using 1 arm) and control conditions in random order. Blood was collected preexercise and 4, 8, 12, 24, 48, and 96 h postexercise. Additional measures included maximal isometric force and midbiceps arm circumference (to detect swelling). Serum and plasma were analyzed for soluble tumor necrosis factor receptor-1 (sTNFR1), IL-6, C-reactive protein, cortisol, and creatine kinase (CK) activity. Relative to the 7:00 AM point in the control condition, diurnal decreases were measured at 12:00 PM and 4:00 PM for IL-6 and at 12:00 PM, 4:00 PM, and 8:00 PM for sTNFR1 and cortisol. sTNFR1, IL-6, CK, swelling, and soreness were higher in the exercise compared with the control condition. The largest of the inflammatory mediator responses was measured for IL-6 8 h postexercise in the exercise (3.00 +/- 3.59 pg/ml) relative to the control condition (1.15 +/- 0.99 pg/ml). The IL-6 response (time-matched exercise--control concentration) at 8 h associated (r > 0.282) with muscle soreness at 24 and 96 h, and the cortisol response at 8 h associated (r > 0.285) with swelling at 8, 24, and 96 h. Thus soreness and swelling, but not CK and strength loss, had a low association with the inflammatory response following eccentric exercise.