Changes in Calpain Activity, Muscle Structure, and Function after Eccentric Exercise

• Published in: Medicine and science in sports and exercise 2010, Vol.42 (1), p.86-95
• Main Authors: RAASTAD, Truls, OWE, Simen Gylterud, PAULSEN, GØran, ENNS, Deborah, OVERGAARD, Kristian, CRAMERI, Regina, KIIL, Steinar, BELCASTRO, Angelo, BERGERSEN, Linda, HALLEN, Jostein
• Format: Article
• Language: English
• Subjects: Adult; Analysis of Variance; Biological and medical sciences; Biopsy; Calpain - metabolism; Exercise - physiology; Fundamental and applied biological sciences. Psychology; Humans; Immunohistochemistry; Leg - physiology; Male; Muscle Contraction - physiology; Muscle Fatigue - physiology; Muscle, Skeletal - anatomy & histology; Muscle, Skeletal - physiology; Myofibrils - physiology; Space life sciences; Torque; Vertebrates: body movement. Posture. Locomotion. Flight. Swimming. Physical exercise. Rest. Sports
• ISSN: 0195-9131; 1530-0315
• DOI: 10.1249/mss.0b013e3181ac7afa

The aim of this study was to investigate changes in muscle function, muscle structure, and calpain activity after high-force eccentric exercise. 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. 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. 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.