期刊
PHYSIOLOGICAL REPORTS
卷 2, 期 11, 页码 -出版社
WILEY
DOI: 10.14814/phy2.12213
关键词
Evans blue dye; lengthening contraction; stretch speed
类别
资金
- Japan Society for the Promotion of Sciences [24300191, 25282160, 23700640, 24659106]
- Grants-in-Aid for Scientific Research [25282160, 24659106, 23700640, 26350638] Funding Source: KAKEN
Exercise involving lengthening contraction (LC) often results in delayed myo-fiber damage and functional deficits over the ensuing days. The present study examined whether the stretch speed of LC is a determinant of damage severity. Under isoflurane anesthesia, LC was repeatedly induced in rat ankle extensor muscles at different stretch speeds (angular velocities of 50, 100, 200, and 400 deg/sec) over a fixed stretch range of motion (90 degrees). The number of muscle fibers labeled with Evans blue dye, a marker of muscle fiber damage associated with increased membrane permeability, increased with the angular velocity of LC (by 20% of all myofibers at 400 deg/sec). Muscle fibers with cross-sectional areas in the range of 3600-4800 mu m(2), corresponding to type IIb fiber size, exhibited the most severe damage as revealed by the largest decrease in the number of fibers 3 days after LC at 200 deg/sec, suggesting that muscle damage occurred preferentially in type IIb myofibers. 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.
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