title: Time course of leukocyte accumulation in human muscle after eccentric exercise.
abstract: 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.
authors.affiliation: Norwegian School of Sport Sciences, Oslo, Norway. goran.paulsen@nih.no
authors.forename: Gøran
authors.initials: G
authors.lastname: Paulsen
authors.forename: Regina
authors.initials: R
authors.lastname: Crameri
authors.forename: Haakon Breien
authors.initials: HB
authors.lastname: Benestad
authors.forename: Jan Gunnar
authors.initials: JG
authors.lastname: Fjeld
authors.forename: Lars
authors.initials: L
authors.lastname: Mørkrid
authors.forename: Jostein
authors.initials: J
authors.lastname: Hallén
authors.forename: Truls
authors.initials: T
authors.lastname: Raastad
mesh_terms: 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
chemical_list: D003402:Creatine Kinase