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Stretch speed-dependent myofiber damage and functional deficits in rat skeletal muscle induced by lengthening contraction.

Mori T, Agata N, Itoh Y, Miyazu-Inoue M, Sokabe M, Taguchi T, Kawakami K - Physiol Rep (2014)

Bottom Line: Isometric torque of dorsiflexion measured 2 days after LC decreased progressively with LC angular velocity (by 68% reduction at 400 deg/sec).The angular velocity of muscle stretch during LC is thus a critical determinant of the degree of damage, and LC appears to damage type IIb fibers preferentially, resulting in a disproportionate reduction in isometric torque.This LC response is an important consideration for the design of physical conditioning and rehabilitation regimens.

View Article: PubMed Central - PubMed

Affiliation: Physical and Occupational Therapy Program, Nagoya University Graduate School of Medicine, Nagoya, Japan Department of Rehabilitation, Nagoya University Hospital, Nagoya, Japan.

No MeSH data available.


Related in: MedlinePlus

Lengthening contraction preferentially damages type IIb fibers. (A, B) Immunofluorescent images of cross‐sectional areas (CSAs) of tibialis anterior (TA) from naïve rats (A) and the lengthening contraction (LC) group 3 days after LC at an angular velocity of 200 deg/sec. (B) Red: Muscle cell membrane labeled with dystrophin antibody. Blue: 4′,6‐diamidino‐2‐phenylindole (DAPI)‐stained nuclei in muscle cells. Note necrotic fibers without dystrophin immunoreactivity (arrow) and nuclear accumulation (arrow head). Scale bar = 100 μm. (C) The proportion of dystrophin‐immunoreactive myofibers against cross‐sectional area (CSA) of myofibers (Bin width: 400 μm2). Open bar: Naïve control (n = 6), Filled bar: LC (n = 6). Note significant differences between the 2 groups in cells with CSAs in the ranges of 1200–1600 μm2, 3600–4000 μm2, 4000–4400 μm2, and 4400–4800 μm2 (P < 0.05–0.0001, two‐way repeated measures ANOVA followed by Sidak's test). (D–F) Immunofluorescent images of different myofiber types in TA sections from a naive animal. Red: Muscle cell membrane labeled with dystrophin antibody. Green: Myosin heavy chain‐positive myofibers: type I (D), IIa (E) and IIb (F). Scale bar = 100 μm. (G) Mean CSAs of myofibers from naive animal. Type IIb fibers (n = 6) are significantly larger than type I (n = 6) and IIa (n = 6) fibers (*P < 0.05, one‐way ANOVA followed by Tukey's post hoc test).
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fig04: Lengthening contraction preferentially damages type IIb fibers. (A, B) Immunofluorescent images of cross‐sectional areas (CSAs) of tibialis anterior (TA) from naïve rats (A) and the lengthening contraction (LC) group 3 days after LC at an angular velocity of 200 deg/sec. (B) Red: Muscle cell membrane labeled with dystrophin antibody. Blue: 4′,6‐diamidino‐2‐phenylindole (DAPI)‐stained nuclei in muscle cells. Note necrotic fibers without dystrophin immunoreactivity (arrow) and nuclear accumulation (arrow head). Scale bar = 100 μm. (C) The proportion of dystrophin‐immunoreactive myofibers against cross‐sectional area (CSA) of myofibers (Bin width: 400 μm2). Open bar: Naïve control (n = 6), Filled bar: LC (n = 6). Note significant differences between the 2 groups in cells with CSAs in the ranges of 1200–1600 μm2, 3600–4000 μm2, 4000–4400 μm2, and 4400–4800 μm2 (P < 0.05–0.0001, two‐way repeated measures ANOVA followed by Sidak's test). (D–F) Immunofluorescent images of different myofiber types in TA sections from a naive animal. Red: Muscle cell membrane labeled with dystrophin antibody. Green: Myosin heavy chain‐positive myofibers: type I (D), IIa (E) and IIb (F). Scale bar = 100 μm. (G) Mean CSAs of myofibers from naive animal. Type IIb fibers (n = 6) are significantly larger than type I (n = 6) and IIa (n = 6) fibers (*P < 0.05, one‐way ANOVA followed by Tukey's post hoc test).

Mentions: The EBD labeling was observed predominantly in larger‐diameter myofibers, suggesting that these larger fibers are preferentially damaged by LC. We labeled cells with an antibody against dystrophin, a cell membrane protein, to measure the CSA distribution of myofibers in naïve rats and rats subjected to LC at 200 deg/sec (Fig. 4A and B). The size distribution was markedly altered by LC, particularly for fibers with CSA >3200 μm2. Two‐way repeated measures ANOVA revealed a significant size group (LC speed) interaction (F[15, 150] = 9.08, P < 0.0001), consistent with differential sensitivity of specific fiber classes to LC. Although the effect of the group was not significant (F[1, 10] = 0.14, P > 0.05), there were significant differences between the control (n = 6) and the combined LC group (n = 6) for fibers with CSAs within the ranges 1200–1600 μm2, 3600–4000 μm2, 4000–4400 μm2, and 4400–4800 μm2 (P < 0.05–0.0001, Sidak's test, Fig. 4C). To gain a rough estimate of the myofiber size range preferentially damaged, we examined the relationship between the size (CSA) and myofiber types in naive animals. CSA ranges of type I fibers (1212.5 ± 141.3 μm2, n = 6, a sample photo in Fig. 4D) and IIa fibers (1327.5 ± 146.5 μm2, n = 6, a sample in Fig. 4E) were less than a half that of the type IIb fibers (3238.1 ± 231.6 μm2, n = 6, a sample in Fig. 4F; P < 0.05, one‐way ANOVA followed by Tukey's post hoc test, Fig. 4G). Given that the largest decrease occurred in fibers >3200 μm2 in CSA, LC appears to preferentially damage type IIb fibers.


Stretch speed-dependent myofiber damage and functional deficits in rat skeletal muscle induced by lengthening contraction.

Mori T, Agata N, Itoh Y, Miyazu-Inoue M, Sokabe M, Taguchi T, Kawakami K - Physiol Rep (2014)

Lengthening contraction preferentially damages type IIb fibers. (A, B) Immunofluorescent images of cross‐sectional areas (CSAs) of tibialis anterior (TA) from naïve rats (A) and the lengthening contraction (LC) group 3 days after LC at an angular velocity of 200 deg/sec. (B) Red: Muscle cell membrane labeled with dystrophin antibody. Blue: 4′,6‐diamidino‐2‐phenylindole (DAPI)‐stained nuclei in muscle cells. Note necrotic fibers without dystrophin immunoreactivity (arrow) and nuclear accumulation (arrow head). Scale bar = 100 μm. (C) The proportion of dystrophin‐immunoreactive myofibers against cross‐sectional area (CSA) of myofibers (Bin width: 400 μm2). Open bar: Naïve control (n = 6), Filled bar: LC (n = 6). Note significant differences between the 2 groups in cells with CSAs in the ranges of 1200–1600 μm2, 3600–4000 μm2, 4000–4400 μm2, and 4400–4800 μm2 (P < 0.05–0.0001, two‐way repeated measures ANOVA followed by Sidak's test). (D–F) Immunofluorescent images of different myofiber types in TA sections from a naive animal. Red: Muscle cell membrane labeled with dystrophin antibody. Green: Myosin heavy chain‐positive myofibers: type I (D), IIa (E) and IIb (F). Scale bar = 100 μm. (G) Mean CSAs of myofibers from naive animal. Type IIb fibers (n = 6) are significantly larger than type I (n = 6) and IIa (n = 6) fibers (*P < 0.05, one‐way ANOVA followed by Tukey's post hoc test).
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fig04: Lengthening contraction preferentially damages type IIb fibers. (A, B) Immunofluorescent images of cross‐sectional areas (CSAs) of tibialis anterior (TA) from naïve rats (A) and the lengthening contraction (LC) group 3 days after LC at an angular velocity of 200 deg/sec. (B) Red: Muscle cell membrane labeled with dystrophin antibody. Blue: 4′,6‐diamidino‐2‐phenylindole (DAPI)‐stained nuclei in muscle cells. Note necrotic fibers without dystrophin immunoreactivity (arrow) and nuclear accumulation (arrow head). Scale bar = 100 μm. (C) The proportion of dystrophin‐immunoreactive myofibers against cross‐sectional area (CSA) of myofibers (Bin width: 400 μm2). Open bar: Naïve control (n = 6), Filled bar: LC (n = 6). Note significant differences between the 2 groups in cells with CSAs in the ranges of 1200–1600 μm2, 3600–4000 μm2, 4000–4400 μm2, and 4400–4800 μm2 (P < 0.05–0.0001, two‐way repeated measures ANOVA followed by Sidak's test). (D–F) Immunofluorescent images of different myofiber types in TA sections from a naive animal. Red: Muscle cell membrane labeled with dystrophin antibody. Green: Myosin heavy chain‐positive myofibers: type I (D), IIa (E) and IIb (F). Scale bar = 100 μm. (G) Mean CSAs of myofibers from naive animal. Type IIb fibers (n = 6) are significantly larger than type I (n = 6) and IIa (n = 6) fibers (*P < 0.05, one‐way ANOVA followed by Tukey's post hoc test).
Mentions: The EBD labeling was observed predominantly in larger‐diameter myofibers, suggesting that these larger fibers are preferentially damaged by LC. We labeled cells with an antibody against dystrophin, a cell membrane protein, to measure the CSA distribution of myofibers in naïve rats and rats subjected to LC at 200 deg/sec (Fig. 4A and B). The size distribution was markedly altered by LC, particularly for fibers with CSA >3200 μm2. Two‐way repeated measures ANOVA revealed a significant size group (LC speed) interaction (F[15, 150] = 9.08, P < 0.0001), consistent with differential sensitivity of specific fiber classes to LC. Although the effect of the group was not significant (F[1, 10] = 0.14, P > 0.05), there were significant differences between the control (n = 6) and the combined LC group (n = 6) for fibers with CSAs within the ranges 1200–1600 μm2, 3600–4000 μm2, 4000–4400 μm2, and 4400–4800 μm2 (P < 0.05–0.0001, Sidak's test, Fig. 4C). To gain a rough estimate of the myofiber size range preferentially damaged, we examined the relationship between the size (CSA) and myofiber types in naive animals. CSA ranges of type I fibers (1212.5 ± 141.3 μm2, n = 6, a sample photo in Fig. 4D) and IIa fibers (1327.5 ± 146.5 μm2, n = 6, a sample in Fig. 4E) were less than a half that of the type IIb fibers (3238.1 ± 231.6 μm2, n = 6, a sample in Fig. 4F; P < 0.05, one‐way ANOVA followed by Tukey's post hoc test, Fig. 4G). Given that the largest decrease occurred in fibers >3200 μm2 in CSA, LC appears to preferentially damage type IIb fibers.

Bottom Line: Isometric torque of dorsiflexion measured 2 days after LC decreased progressively with LC angular velocity (by 68% reduction at 400 deg/sec).The angular velocity of muscle stretch during LC is thus a critical determinant of the degree of damage, and LC appears to damage type IIb fibers preferentially, resulting in a disproportionate reduction in isometric torque.This LC response is an important consideration for the design of physical conditioning and rehabilitation regimens.

View Article: PubMed Central - PubMed

Affiliation: Physical and Occupational Therapy Program, Nagoya University Graduate School of Medicine, Nagoya, Japan Department of Rehabilitation, Nagoya University Hospital, Nagoya, Japan.

No MeSH data available.


Related in: MedlinePlus