Creatine kinase release and clearance using MM variants following repeated bouts of eccentric exercise

Purpose: This study investigated the release and clearance of plasma CK- MM (muscle) isoforms following two bouts of eccentric exercise to determine whether enhanced enzyme clearance could in part explain the blunted creatine kinase (CK) response to a second bout of exercise. Methods: Nonweight trained college-aged male subjects performed both bouts of 50 forced lengthening contractions of the forearm flexor muscles separated by 6 d either with the same arm (CON; N = 4) or with one arm followed by the contralateral arm (EXP; N = 4). Range of motion, arm circumference, maximal isometric strength, perceived muscle soreness, total CK (TCK), and MM variants were assessed. Each MM isoform was measured as a percentage of TCK activity and in absolute activity (IU·L^-1) following isoelectric separation and densitometry. The MM1:MM3 ratio, calculated from absolute concentrations, was used to indicate periods of release and clearance. Results: Non-CK criterion measures indicated that similar damage occurred in both arms for EXP (P > 0.05), whereas CON exhibited a blunted response on bout 2 (P < 0.01). Postbout 1, TCK peaked at 96 h for CON (3530 ± 927 IU·L^-1) and EXP (6683 ± 433 IU·L^-1) (P < 0.01). Postbout 2, CON TCK showed no additional increase; however, a second rise in EXP TCK reached its highest point by clay 5 (3602 ± 1190 IU · L^-1). Expectedly, %MM1 and the MM1:MM3 ratio were increased after bout I in both groups (P < 0.01). New CK release was observed postbout 2 in both groups as indicated by an increase in %MM1 (P < 0.01), despite no increase in TCK after bout 2 for CON and a smaller CK response for EXP. Conclusion: Accelerated clearance of CK seems to be one factor contributing to the blunted response of this enzyme following a repeated bout of exercise.