SKELETAL TROPONIN-I AS A MARKER OF EXERCISE-INDUCED MUSCLE DAMAGE

The utility of skeletal troponin I (sTnI) as a plasma marker of skelet al muscle damage after exercise was compared against creatine kinase ( CK), myoglobin (Mb), and myosin heavy chain (MHC) fragments. These mar kers were serially measured in normal physical education teacher train ees after four different exercise regimens: 20 min of level or downhil l (16% decline) running (intensity: 70% maximal O-2 uptake), high-forc e eccentric contractions (70 repetitions), or high-force isokinetic co ncentric contractions of the quadriceps group (40 repetitions). Eccent rically biased exercise (downhill running and eccentric contractions) promoted greater increases in all parameters. The highest plasma conce ntration were found after downhill running {median peaks: 309 U/l CK c oncentration ([CK])}, 466 mu g/l Mb concentration ([Mb]), 1,021 mu U/l MHC concentration ([MHC]), and 27.3 mu g/l sTnI concentration ([sTnI] ). Level running produced a moderate response (median peaks: 178 U/l [ CK], 98 mu g/l [Mb], 501 mu U/l [MHC], and 6.6 mu g/l [sTnI]), whereas the concentric contraction protocol did not elicit significant change s in any of the markers assayed. sTnI increased and peaked in parallel to CK and stayed elevated (>2.2 mu g/l) for at least 1-2 days after e xercise. In contrast to MHC, sTnI is an initial, specific marker of ex ercise-induced muscle injury, which may be partly explained by their d ifferent intracellular compartmentation with essentially no (MHC <0.1% ) or a small soluble pool(sTnI: median 3.4%).