RAPID ADAPTATION TO ECCENTRIC EXERCISE-INDUCED MUSCLE DAMAGE

This study examined eccentric exercise-induced muscle damage and rapid adaptation. Twenty-two male subjects performed 70 eccentric actions w ith the knee extensors. Group A (n = 11) and group B (n = 11) repeated the same exercise 4 and 13 days after the initial bout, respectively. Criterion measures included muscle soreness, muscle force generation (vertical jump height on a Kistler platform), and plasma levels of cre atine kinase (CK), slow-twitch skeletal (cardiac beta-type) myosin hea vy chains (MHC), and cardiac troponin I. Subjects were tested preexerc ise and up to day 4 following each bout. The initial exercise resulted in an increase in CK and MHC, a decrement in muscle force, and delaye d onset muscle soreness in all participants. CK and MHC release correl ated closely (rho = 0.73, p = 0.0001), both did not correlate with the decrement in muscle force generation after exercise. Because cardiac troponin I could not be detected in all samples, which excluded a prot ein release from the heart (cardiac beta-type MHC), this finding provi des evidence for a injury of slow-twitch skeletal muscle fibers in res ponse to eccentric contractions. Repetition of the initial eccentric e xercise bout after 13 days (group B) did not cause muscle soreness, a decrement in muscle reaction force with vertical jump or significant c hanges in plasma MHC and CK concentrations, whereas in case of repetit ion after 4 days (group A) only the significant increases in CK and MH C were abolished. The decrement in reaction force with vertical jump d id not differ significantly from that after the initial exercise sessi on, but perceived muscle soreness was less pronounced. Performance of one bout of eccentric exercise produced a greater resistance of the ex ercised muscle to a subsequent bout of eccentric exercise.