EFFECTS OF PROLONGED STRENUOUS ENDURANCE EXERCISE ON PLASMA MYOSIN HEAVY-CHAIN FRAGMENTS AND OTHER MUSCULAR PROTEINS - CYCLING VS RUNNING

Background. This study evaluates creatine kinase, myosin heavy chain, and cardiac troponin blood levels following three types of exercise: 1 ) short-distance uphill or downhill running; 2) alpine ultramarathon; and 3) alpine long-distance cycling. Methods. Experimental design: Com parative field study; followup up to 10 days. Setting: Department of S ports Medicine. All biochemical markers were analysed at the Departmen t of Medical Chemistry and Biochemistry. Patients or participants: Sub jects included healthy, trained males (N=53). All subjects were nonsmo kers and free from medication prior to and during the study. Each volu nteer was an experienced runner or cyclist, who had at least once succ essfully finished the Swiss Alpine Marathon of Davos or the Otztal-Rad marathon before. Interventions: Running or cycling. Measures: Plasma c oncentrations of creatine kinase, myosin heavy chain fragments and car diac troponins were measured to diagnose skeletal and cardiac muscle d amage, respectively. Results. Skeletal muscle protein release is marke dly different between uphill and downhill running, with very little ev idence for muscle damage in the uphill runners. There is considerable muscle protein leakage in the ultramarathoners (67 km distance; 30 km downhill running). In contrast, only modest amounts of skeletal muscle damage are found after alpine long-distance cycling (230 km distance) . Conclusions. This study proves that there is slow-twitch skeletal mu scle fiber damage after prolonged strenuous endurance exercise and sho rt-distance downhill running. Exhaustive endurance exercise involving downhill running and short-distance downhill running lead to more pron ounced injury than strenuous endurance exercise involving concentric a ctions. From our results there is no reason for suggesting that prolon ged intense exercise may induce myocardial injury in symptomless athle tes without cardiac deseases.