Time course of leukocyte accumulation in human muscle after eccentric exercise.
OBJECTIVE
To investigate the time 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 x s(-1)). Before and at regular intervals for 7 d after exercise, force-generating capacity was measured with maximal concentric knee extensions (60 degrees x 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 h 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 on 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 in the 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 part 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 d 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).


CONCLUSIONS
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.
Paulsen
Gøran
G
Norwegian School of Sport Sciences, Oslo, Norway. goran.paulsen@nih.no
Crameri
Regina
R
Benestad
Haakon Breien
HB
Fjeld
Jan Gunnar
JG
Mørkrid
Lars
L
Hallén
Jostein
J
Raastad
Truls
T
D000328:Adult; D000704:Analysis of Variance; D001706:Biopsy; D003402:Creatine Kinase / Q000097:blood; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007150:Immunohistochemistry; D007249:Inflammation / Q000503:physiopathology; D007962:Leukocytes / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000166:cytology* / Q000000981:diagnostic imaging / Q000502:physiology; D011877:Radionuclide Imaging; D020127:Recovery of Function; D018709:Statistics, Nonparametric; D013997:Time Factors
D003402:Creatine Kinase