Sarcomere Disruptions of Slow Fiber Resulting From Mountain Ultramarathon.

OBJECTIVE: To investigate changes after a mountain ultramarathon (MUM) in the serum concentration of fast (FM) and slow (SM) myosin isoforms, which are fiber-type-specific sarcomere proteins. The changes were compared against creatine kinase (CK), a widely used fiber-sarcolemma-damage biomarker, and cardiac troponin I (cTnI), a widely used cardiac biomarker. METHODS: Observational comparison of response in a single group of 8 endurance-trained amateur athletes. Time-related changes in serum levels of CK, cTnI, SM, and FM from competitors were analyzed before, 1 h after the MUM, and 24 and 48 h after the start of the MUM by 1-way ANOVA for repeated measures or Friedman and Wilcoxon tests. Pearson correlation coefficient was employed to examine associations between variables. RESULTS: While SM was significantly (P = .009) increased in serum 24 h after the beginning of the MUM, FM and cTnI did not change significantly. Serum CK activity peak was observed 1 h after the MUM (P = .002). Moreover, serum peaks of CK and SM were highly correlated (r = .884, P = .004). CONCLUSIONS: Since there is evidence of muscle damage after prolonged mountain running, the increase in SM serum concentration after a MUM could be indirect evidence of slow- (type I) fiber-specific sarcomere disruptions.

Muscle enzyme and fiber type-specific sarcomere protein increases in serum after inertial concentric-eccentric exercise.

Muscle damage induced by inertial exercise performed on a flywheel device was assessed through the serum evolution of muscle enzymes, interleukin 6, and fiber type-specific sarcomere proteins such as fast myosin (FM) and slow myosin (SM). We hypothesized that a model of muscle damage could be constructed by measuring the evolution of serum concentration of muscle proteins following inertial exercise, according to their molecular weight and the fiber compartment in which they are located. Moreover, by measuring FM and SM, the type of fibers that are affected could be assessed. Serum profiles were registered before and 24, 48, and 144 h after exercise in 10 healthy and recreationally active young men. Creatine kinase (CK) and CK-myocardial band isoenzyme increased in serum early (24 h) and returned to baseline values after 48 h. FM increased in serum late (48 h) and remained elevated 144 h post-exercise. The increase in serum muscle enzymes suggests increased membrane permeability of both fast and slow fibers, and the increase in FM reveals sarcomere disruption as well as increased membrane permeability of fast fibers. Consequently, FM could be adopted as a fiber type-specific biomarker of muscle damage.