title: Changes in calpain activity, muscle structure, and function after eccentric exercise.
abstract: OBJECTIVE
  The aim of this study was to investigate changes in muscle function, muscle structure, and calpain activity after high-force eccentric exercise.
  
  
  METHODS
  Eleven healthy males performed 300 maximal voluntary eccentric actions with knee extensors in one leg. Maximal force-generating capacity was measured before exercise and regularly during the next 7 d. Biopsies from musculus vastus lateralis were taken in both control and exercised legs 0.5, 4, 8, 24, 96, and 168 h after exercise for evaluation of myofibrillar structure, extracellular matrix proteins, and calpain activity.
  
  
  RESULTS
  In the exercised leg, peak torque was reduced by 47 +/- 5% during exercise and was still 22 +/- 5% lower than baseline 4 d after the exercise. Calpain activity was three times higher in the exercised leg compared with the control leg 30 min after exercise. Myofibrillar disruptions were observed in 36 +/- 6% of all fibers in exercised muscle and in 2 +/- 1% of fibers in control muscle. The individual reductions in peak torque correlated with the proportion of fibers with myofibrillar disruptions (r = 0.89). The increase in calpain activity was not correlated to the proportion of fibers with myofibrillar disruptions. Nevertheless, the characteristics of the myofibrillar disruptions mimicked calpain-mediated degradation of myofibrils. Tenascin-C and the N-terminal propeptide of procollagen type III showed increased staining intensity on cross-sections 4-7 d after the exercise.
  
  
  CONCLUSIONS
  Myofibrillar disruptions seem to be a main cause for the long-lasting reduction in force-generating capacity after high-force eccentric exercise. The increase in calpain activity, but the lack of a relationship between calpain activity and the amount of muscle damage, suggests multiple roles of calpain in the damage and repair process.
authors.affiliation: Norwegian School of Sport Sciences, Oslo, Norway. truls.raastad@nih.no
authors.forename: Truls
authors.initials: T
authors.lastname: Raastad
authors.forename: Simen Gylterud
authors.initials: SG
authors.lastname: Owe
authors.forename: Gøran
authors.initials: G
authors.lastname: Paulsen
authors.forename: Deborah
authors.initials: D
authors.lastname: Enns
authors.forename: Kristian
authors.initials: K
authors.lastname: Overgaard
authors.forename: Regina
authors.initials: R
authors.lastname: Crameri
authors.forename: Steinar
authors.initials: S
authors.lastname: Kiil
authors.forename: Angelo
authors.initials: A
authors.lastname: Belcastro
authors.forename: Linda
authors.initials: L
authors.lastname: Bergersen
authors.forename: Jostein
authors.initials: J
authors.lastname: Hallén
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001706:Biopsy; D002154:Calpain / Q000378:metabolism*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007150:Immunohistochemistry; D007866:Leg / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000502:physiology*; D009210:Myofibrils / Q000502:physiology; D019415:Torque
chemical_list: D002154:Calpain