Changes in calpain activity, muscle structure, and function after eccentric exercise.
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.
Raastad
Truls
T
Norwegian School of Sport Sciences, Oslo, Norway. truls.raastad@nih.no
Owe
Simen Gylterud
SG
Paulsen
Gøran
G
Enns
Deborah
D
Overgaard
Kristian
K
Crameri
Regina
R
Kiil
Steinar
S
Belcastro
Angelo
A
Bergersen
Linda
L
Hallén
Jostein
J
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
D002154:Calpain