Preferential type II muscle fiber damage from plyometric exercise.
BACKGROUND
Plyometric training has been successfully used in different sporting contexts. Studies that investigated the effect of plyometric training on muscle morphology are limited, and results are controversial with regard to which muscle fiber type is mainly affected.


OBJECTIVE
To analyze the skeletal muscle structural and ultrastructural change induced by an acute bout of plyometric exercise to determine which type of muscle fibers is predominantly damaged.


METHODS
Descriptive laboratory study.


METHODS
Research laboratory.


METHODS
Eight healthy, untrained individuals (age = 22 ± 1 years, height = 179.2 ± 6.4 cm, weight = 78.9 ± 5.9 kg).


METHODS
Participants completed an acute bout of plyometric exercise (10 sets of 10 squat-jumps with a 1-minute rest between sets).


METHODS
Blood samples were collected 9 days and immediately before and 6 hours and 1, 2, and 3 days after the acute intervention. Muscle samples were collected 9 days before and 3 days after the exercise intervention. Blood samples were analyzed for creatine kinase activity. Muscle biopsies were analyzed for damage using fluorescent and electron transmission microscopy.


RESULTS
Creatine kinase activity peaked 1 day after the exercise bout (529.0 ± 317.8 U/L). Immunofluorescence revealed sarcolemmal damage in 155 of 1616 fibers analyzed. Mainly fast-twitch fibers were damaged. Within subgroups, 7.6% of type I fibers, 10.3% of type IIa fibers, and 14.3% of type IIx fibers were damaged as assessed by losses in dystrophin staining. Similar damage was prevalent in IIx and IIa fibers. Electron microscopy revealed clearly distinguishable moderate and severe sarcomere damage, with damage quantifiably predominant in type II muscle fibers of both the glycolytic and oxidative subtypes (86% and 84%, respectively, versus only 27% of slow-twitch fibers).


CONCLUSIONS
We provide direct evidence that a single bout of plyometric exercise affected mainly type II muscle fibers.
Department of Physiological Sciences, Stellenbosch University, South Africa. filippo.macaluso@unipa.it
Filippo
F
Macaluso
Ashwin W
AW
Isaacs
Kathryn H
KH
Myburgh
D003402:Creatine Kinase / Q000097:blood; D015444:Exercise / Q000502:physiology; D006801:Humans; D009119:Muscle Contraction; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology*; D018482:Muscle, Skeletal / Q000293:injuries* / Q000502:physiology*; D059385:Plyometric Exercise; D012026:Reflex, Stretch; D055815:Young Adult
D003402:Creatine Kinase