Preferential Type II Muscle Fiber Damage From Plyometric Exercise

Abstract

Context: 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.Design: Descriptive laboratory study. Setting: Research laboratory.Patients or Other Participants: Eight healthy, untrained individuals (age ¼ 22 6 1 years, height ¼ 179.2 6 6.4 cm, weight ¼ 78.9 6 5.9 kg).Intervention(s): Participants completed an acute bout of plyometric exercise (10 sets of 10 squat-jumps with a 1-minute rest between sets).Main Outcome Measure(s): 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 6 317.8 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.Key Words: eccentric exercise, sarcomere, Z-disk streaming, electron transmission microscopy, creatine kinase, dystrophin Key PointsPlyometric exercise mainly affected the fast-twitch muscle fibers, damaging both the sarcolemma and the sarcomere at the site of the Z-disk. Athletic trainers should avoid prescribing high-volume plyometric exercise bouts within quick succession or after other forms of high-intensity exercise that are known to stress the fast-twitch muscle fibers, so that athletes have sufficient time to regenerate damaged fibers. P lyometrics refers to exercise that exploits the stretchshortening cycle, which proceeds with the rapid stretch of a muscle (eccentric phase), followed by rapid (150-millisecond) shortening of the same muscle (concentric phase), which results in increased force and power output of the activated muscles.1 This type of training has been successfully used in different sporting contexts to improve strength, muscle power, coordination, and athletic performance by inducing greater motor-unit recruitment, enhanced r...

Satellite cell pool expansion is affected by skeletal muscle characteristics

“…One way in which human skeletal muscle differs from that of the mouse is with regard to the heterogeneity of fiber type within the same muscle. The vastus lateralis of mouse contains almost exclusively type II muscle fibers, whereas the human vastus lateralis fiber type distribution varies substantially . We have preliminary evidence that the increased SC count after a week of recovery from DHR may be correlated positively with MHC type II percentage expressed in the skeletal muscle analyzed.…”

Acute change of titin at mid-sarcomere remains despite 8 wk of plyometric training

“…During sets, participants were allowed to move around freely and do general stretching for no longer than 30 s. All participants had to complete 100 jumps, jumps where participants could not maintain their target jump height, trunk position, or 90°knee joint angle were not considered. Participants were stopped and given 1-min rest period before having to complete that set (30).…”

The Effects of Short-term Exercise Training on Peak-Torque Are Time- and Fiber-Type Dependent

“…Biochemical, histochemical, and immunocytochemical studies observed greater susceptibility to damage in type II muscle fibers, fibers comprising type IIa and IIx myosinheavy chains, and satellite cells associated with type II fibers in human (4,15,16,31,36), animal (35,50), and primary cell cultures following bouts of eccentric exercise or passive mechanical stretch exerted on myotubes (18). However, there is also evidence for a preferential disruption in ST muscle fibers (1,20,38,50).…”

“…Although it is well documented that high-force eccentric contractions produce myofibrillar disruption (8,26,28), biochemical, histochemical, and immunocytochemical studies report inconsistent findings concerning the muscle fiber-type specificity of the disruption. Several studies observed greater susceptibility to damage in type II muscle fibers, fibers comprising type IIa and IIx myosin-heavy chains, and satellite cells associated with type II fibers in human (4,15,16,31,36), animal (35,50), and other models (18) following bouts of eccentric exercise. However, there is also evidence for a preferential disruption in type I muscle fibers (1,20,38,50).…”