Elevated CK-MB Levels in Marathon Runners

Abstract

To the Editor.— The report by Siegel et al on elevations of serum CK-MB isoenzyme levels in marathon runners contains several inaccuracies. The MB level is alleged to correlate with the serum myoglobin level as a sensitive biochemical marker for the extent of exertional In the reference cited for this correlation CK isoenzymes were not measured. 1 The correlation was between total CK levels and rhabdomyolysis. It is further asserted that mild abnormalities of CK-MB can be seen after recreational exercise of unselected volunteers. Again the authors in the reference cited to support this contention evaluated only total CK and did not measure isoenzymes. 2 Kaman et al, 3 using electrophoresis, could not detect elevations of CK-MB in the blood of joggers after near-maximum exercise. Dr Siegel and associates state that unlike enzymes widely distributed in human tissues, creatine kinase is found only in muscle cells. Skeletal muscle and