Why Does Muscle Strain Occur Regionally? An Examination from The View of Heterogeneous Elongation of Sarcomere
【Supercategory：7. DESCENTE SPORTS SCIENCE Subcategory：7.43 Vol.43】
ABSTRACT
It is generally considered that sarcomere length becomes nonuniform after eccentric contraction. This phenomenon might be related to muscle strain which occurs regionally along muscle fibers. However, the existence of this sarcomere length dispersion has not been clarified experimentally. Therefore, we directly measured sarcomere length after an eccentric contraction. Single skinned fiber（psoas, N=4） was obtained from a New Zealand white rabbit. This isolated single fiber was set under an inverted microscope to directly measure the sarcomere length. In the eccentric condition, fibers were activated isometrically, and then, actively stretched by 25% of the initial fiber 2 s, followed by a 15 s isometric contraction. In the isometric condition, fibers were passively stretched by 25% of the initial fiber length in 2 s,and then, activated isometrically. The isometric force obtained after the active stretch was compared to that obtained in the purely isometric contraction. At the same time, sarcomere length was measured. As result, the isometric force was significantly larger in the eccentric condition （0.44 ± 0.23 mN） than in the isometric condition （0.38± 0.20 mN） （p = 0.039）. The average sarcomere length and the standard deviation were 2.8 ± 0.3 μm for the eccentric condition and 2.8 ± 0.4 μm for the isometric condition, respectively. An F-test revealed that the variation of sarcomere length was not statistically different between these conditions. Unlike our hypothesis, the variation of the sarcomere length in the eccentric condition was not different compared to that in the isometric condition. This result indicates that the theory of sarcomere length nonuniformity should be reconsidered, and other factors, which might be titin, should contribute to the stable sarcomere length even after the eccentric contraction. Based on this finding, muscle strain would not be explained by sarcomere length nonuniformity.
DECENTE SPORTS SCIENCE Vol.43/The DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE
It is generally considered that sarcomere length becomes nonuniform after eccentric contraction. This phenomenon might be related to muscle strain which occurs regionally along muscle fibers. However, the existence of this sarcomere length dispersion has not been clarified experimentally. Therefore, we directly measured sarcomere length after an eccentric contraction. Single skinned fiber（psoas, N=4） was obtained from a New Zealand white rabbit. This isolated single fiber was set under an inverted microscope to directly measure the sarcomere length. In the eccentric condition, fibers were activated isometrically, and then, actively stretched by 25% of the initial fiber 2 s, followed by a 15 s isometric contraction. In the isometric condition, fibers were passively stretched by 25% of the initial fiber length in 2 s,and then, activated isometrically. The isometric force obtained after the active stretch was compared to that obtained in the purely isometric contraction. At the same time, sarcomere length was measured. As result, the isometric force was significantly larger in the eccentric condition （0.44 ± 0.23 mN） than in the isometric condition （0.38± 0.20 mN） （p = 0.039）. The average sarcomere length and the standard deviation were 2.8 ± 0.3 μm for the eccentric condition and 2.8 ± 0.4 μm for the isometric condition, respectively. An F-test revealed that the variation of sarcomere length was not statistically different between these conditions. Unlike our hypothesis, the variation of the sarcomere length in the eccentric condition was not different compared to that in the isometric condition. This result indicates that the theory of sarcomere length nonuniformity should be reconsidered, and other factors, which might be titin, should contribute to the stable sarcomere length even after the eccentric contraction. Based on this finding, muscle strain would not be explained by sarcomere length nonuniformity.
DECENTE SPORTS SCIENCE Vol.43/The DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE
| Researcher | Atsuki Fukutani |
|---|---|
| University or institution | Ritsumeikan University |
Keywords
skeletal muscle, skinned fiber, sarcomere, eccentric contraction, heterogeneity