title: Stretch speed-dependent myofiber damage and functional deficits in rat skeletal muscle induced by lengthening contraction.
abstract: Exercise involving lengthening contraction (LC) often results in delayed myofiber 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°). 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 μm(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.
authors.affiliation: Physical and Occupational Therapy Program, Nagoya University Graduate School of Medicine, Nagoya, Japan Department of Rehabilitation, Nagoya University Hospital, Nagoya, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Mori
authors.affiliation: Physical and Occupational Therapy Program, Nagoya University Graduate School of Medicine, Nagoya, Japan.
authors.forename: Nobuhide
authors.initials: N
authors.lastname: Agata
authors.affiliation: Physical and Occupational Therapy Program, Nagoya University Graduate School of Medicine, Nagoya, Japan.
authors.forename: Yuta
authors.initials: Y
authors.lastname: Itoh
authors.affiliation: Aichi Medical College for Physical and Occupational Therapy, Kiyosu, Japan.
authors.forename: Masumi
authors.initials: M
authors.lastname: Miyazu-Inoue
authors.affiliation: Mechanobiology Laboratory, Nagoya University Graduate School of Medicine, Nagoya, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Sokabe
authors.affiliation: Department of Neuroscience II, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Taguchi
authors.affiliation: Physical and Occupational Therapy Program, Nagoya University Graduate School of Medicine, Nagoya, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Kawakami
keywords: Evans blue dye; lengthening contraction; stretch speed