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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

Stretch speed‐dependent loss of muscle function. (A) Evoked torque of dorsiflexion induced by isometric contraction of the ankle extensor muscles measured 2 days after lengthening contraction (LC). (A) Torque decreases as a function of increased angular velocity from 50 to 400 deg/sec. Data are shown as mean ± SEM. Number of animals tested is shown in parenthesis in each bar. Bars with different symbols indicate significant differences. Number of samples pre‐LC (n = 41). (B) Correlation between the number of Evans blue dye (EBD)‐positive myofibers and the isometric dorsiflexion torque generated during LC. Note the significant negative correlation between the two parameters (Spearman r = −0.85, P < 0.0001).
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fig05: Stretch speed‐dependent loss of muscle function. (A) Evoked torque of dorsiflexion induced by isometric contraction of the ankle extensor muscles measured 2 days after lengthening contraction (LC). (A) Torque decreases as a function of increased angular velocity from 50 to 400 deg/sec. Data are shown as mean ± SEM. Number of animals tested is shown in parenthesis in each bar. Bars with different symbols indicate significant differences. Number of samples pre‐LC (n = 41). (B) Correlation between the number of Evans blue dye (EBD)‐positive myofibers and the isometric dorsiflexion torque generated during LC. Note the significant negative correlation between the two parameters (Spearman r = −0.85, P < 0.0001).

Mentions: Concomitant with fiber damage, we also observed functional deficits following LC. The isometric torque (generated by electrically induced dorsiflexion of ankle extensors) measured 2 days after LC was significantly lower compared with the pre‐LC baseline (26.0 ± 0.4 mNm, n = 41, Fig. 5A) and decreased progressively with LC speed (50 deg/sec: 22.7 ± 0.5 mNm, n = 7, 13% decrease from baseline; 100 deg/sec: 15.7 ± 1.4 mNm, n = 8, 40% decrease; 200 deg/sec: 9.9 ± 0.5 mNm, n = 19; 62% decrease; 400 deg/sec: 8.4 ± 1.1 mNm, n = 7; 68% decrease). The loss in torque was not different between the 200 deg/sec and 400 deg/sec treatment groups. There was a significant negative correlation between the number of EBD‐positive myofibers in the entire CSA of TA and the isometric dorsiflexion torque measured 2 days after LC (Spearman r = −0.85, P < 0.0001, Fig. 5B), strongly suggesting that functional loss is a direct result of fiber damage.


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)

Stretch speed‐dependent loss of muscle function. (A) Evoked torque of dorsiflexion induced by isometric contraction of the ankle extensor muscles measured 2 days after lengthening contraction (LC). (A) Torque decreases as a function of increased angular velocity from 50 to 400 deg/sec. Data are shown as mean ± SEM. Number of animals tested is shown in parenthesis in each bar. Bars with different symbols indicate significant differences. Number of samples pre‐LC (n = 41). (B) Correlation between the number of Evans blue dye (EBD)‐positive myofibers and the isometric dorsiflexion torque generated during LC. Note the significant negative correlation between the two parameters (Spearman r = −0.85, P < 0.0001).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4255819&req=5

fig05: Stretch speed‐dependent loss of muscle function. (A) Evoked torque of dorsiflexion induced by isometric contraction of the ankle extensor muscles measured 2 days after lengthening contraction (LC). (A) Torque decreases as a function of increased angular velocity from 50 to 400 deg/sec. Data are shown as mean ± SEM. Number of animals tested is shown in parenthesis in each bar. Bars with different symbols indicate significant differences. Number of samples pre‐LC (n = 41). (B) Correlation between the number of Evans blue dye (EBD)‐positive myofibers and the isometric dorsiflexion torque generated during LC. Note the significant negative correlation between the two parameters (Spearman r = −0.85, P < 0.0001).
Mentions: Concomitant with fiber damage, we also observed functional deficits following LC. The isometric torque (generated by electrically induced dorsiflexion of ankle extensors) measured 2 days after LC was significantly lower compared with the pre‐LC baseline (26.0 ± 0.4 mNm, n = 41, Fig. 5A) and decreased progressively with LC speed (50 deg/sec: 22.7 ± 0.5 mNm, n = 7, 13% decrease from baseline; 100 deg/sec: 15.7 ± 1.4 mNm, n = 8, 40% decrease; 200 deg/sec: 9.9 ± 0.5 mNm, n = 19; 62% decrease; 400 deg/sec: 8.4 ± 1.1 mNm, n = 7; 68% decrease). The loss in torque was not different between the 200 deg/sec and 400 deg/sec treatment groups. There was a significant negative correlation between the number of EBD‐positive myofibers in the entire CSA of TA and the isometric dorsiflexion torque measured 2 days after LC (Spearman r = −0.85, P < 0.0001, Fig. 5B), strongly suggesting that functional loss is a direct result of fiber damage.

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