VARIABILITY IN SERUM CREATINE-KINASE RESPONSE AFTER ECCENTRIC EXERCISE OF THE ELBOW FLEXORS

There is a large inter-subject variability in serum creatine kinase (C K) response after eccentric exercise. This study examined and compared the variability of CK activity, other serum protein increases (aspart ate aminotransferase, alanine aminotransferase, lactate dehydrogenase, aldolase, myoglobin), changes in muscle damage indicators (maximal is ometric force: MIF, relaxed and flexed elbow joint angle: RANG and FAN G, circumference: CIR, and muscle soreness level: SOR), and changes in magnetic resonance (MR) images. Ten male subjects (21.7 +/- 1.6 yrs) performed 24 maximal eccentric actions of the elbow flexors, and measu rements except MR images were taken immediately before and after, and for 10 days after exercise. MR images were taken 7 days after exercise . A large variability in peak CK response (236 - 25,244 IU . l(-1)) wa s found among subjects. Spearman rank-order correlation coefficients ( r) revealed significant correlations of peak CK with peak serum protei n levels (r = 0.79-0.95), peak changes in MIF (r = 0.73-0.79), RANG (r = 0.69), and CIR (r = 0.91). The higher the peak CK levels, the more profound the abnormality in the MR images and the larger the changes i n MR signal intensity (r = 0.90 - 0.94). It is concluded that the larg e variability in CK response after exercise seems to be related to the variability in exercise-induced muscle damage.