title: Postactivation potentiation, fiber type, and twitch contraction time in human knee extensor muscles.
abstract: In small mammals, muscles with shorter twitch contraction times and a predominance of fast-twitch, type II fibers exhibit greater posttetanic twitch force potentiation than muscles with longer twitch contraction times and a predominance of slow-twitch, type I fibers. In humans, the correlation between potentiation and fiber-type distribution has not been found consistently. In the present study, postactivation potentiation (PAP) was induced in the knee extensors of 20 young men by a 10-s maximum voluntary isometric contraction (MVC). Maximal twitch contractions of the knee extensors were evoked before and after the MVC. A negative correlation (r = -0. 73, P < 0.001) was found between PAP and pre-MVC twitch time to peak torque (TPT). The four men with the highest (HPAP, 104 +/- 11%) and lowest (LPAP, 43 +/- 7%) PAP values (P < 0.0001) underwent needle biopsies of vastus lateralis. HPAP had a greater percentage of type II fibers (72 +/- 9 vs. 39 +/- 7%, P < 0.001) and shorter pre-MVC twitch TPT (61 +/- 12 vs. 86 +/- 7 ms, P < 0.05) than LPAP. These data indicate that, similar to the muscles of small mammals, human muscles with shorter twitch contraction times and a higher percentage of type II fibers exhibit greater PAP.
authors.affiliation: Department of Kinesiology and Medicine, McMaster University, Hamilton, Ontario, Canada.
authors.forename: T
authors.initials: T
authors.lastname: Hamada
authors.forename: D G
authors.initials: DG
authors.lastname: Sale
authors.forename: J D
authors.initials: JD
authors.lastname: MacDougall
authors.forename: M A
authors.initials: MA
authors.lastname: Tarnopolsky
mesh_terms: D000328:Adult; D004576:Electromyography; D006801:Humans; D007717:Knee / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000145:classification* / Q000502:physiology; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D013997:Time Factors