Time Course of Leukocyte Accumulation in Human Muscle after Eccentric Exercise

PAULSEN. G., R. CRAMERI, H. B. BENESTAD, J. G. HELD. L. MORKRID, J. HALLEN, and T. RAASTAD. Time course of Leukocyte Accumulation in Human Muscle after Eccentric Exercise. Med. Sci. Sports Exerc., Vol. 42, No. 1, pp. 75-85, 2010. Put-pose: To investigate the little course of leukocyte accumulation in eccentric exercised human muscles and its relation to recovery of muscle function and soreness. Methods: Eleven young males performed 300 unilateral. maximal voluntary, eccentric actions with the musculus quadriceps femoris (30 degrees.s(-1)). Before and at regular intervals for 7 d after exercise, force-generating capacity was measured with maximal concentric knee extensions (60 degrees.s(-1)). Accumulation of radiolabeled (autologous) leukocytes was measured with scintigraphy. Biopsies from musculus vastus lateralis were obtained 0.5, 4, 8, 24, 96, and 168 It after exercise from both the exercised leg and the control leg. Muscle cross-sections were stained with antibodies against leukocytes (CD16 and CD68). Muscle soreness was rated oil a visual analog scale. Results: Immediately after exercise, the Subjects' ability to generate force was reduced by 47 +/- 5%. Muscle function recovered slowly and was not fully restored after 1 wk. Radiolabeled leukocytes accumulated ill file Muscles during the first hour (3-24 h) after exercise, and leukocytes were at the same time observed histologically. primarily in the endomysium and perimysium. A pail of the accumulated radiolabeled leukocytes appeared to be located within local blood vessels. The highest numbers of CD16(+) and CD68(+) cells were found 4 and 7 (1 after exercise. There was a positive correlation between accumulation of radiolabeled leukocytes and muscle weakness measured 1-3 d after exercise (r = 0.8. P < 0.05) and, surprisingly. a negative correlation between radiolabeled leukocyte accumulation and Muscle soreness (r = -0.96, P < 0.01). Conclusion: Exercise-induced Muscle damage initiated a rapid local inflammatory response that gradually increased over the next days, Halted recovery Of muscle function Was associated with local accumulation of leukocytes, whereas muscle soreness could not be explained by the presence of leukocytes.