Author(s): NITA, Y., OGA, R., CHEN, Y.C., NISHIYAMA, H., TAMAKI, H., Institution: NATIONAL INSTITUTE OF FITNESS AND SPORTS IN KANOYA, Country: JAPAN, Abstract-ID: 994

INTRODUCTION:
Sarcomere length fluctuates with muscle stretching and shortening. There may also be variability in the lengths of individual sarcomeres because of differences in skeletal muscle regions and joint angles. Mechanical stress applied to locations with nonuniform sarcomere lengths is likely to induce muscle damage. Therefore, understanding the joint angles and regions associated with sarcomere nonuniformity is important for protection against skeletal muscle damage. We examined the nonuniformity in sarcomere lengths associated with various ankle joint angles and muscle regions in the rat tibialis anterior (TA) muscle.
METHODS:
Nine-week-old male Fischer 344 rats (n = 9) were subjected to perfusion fixation with their ankle joints at 40 degrees, 110 degrees, and 180 degrees on the left and right legs, respectively. The TA muscle was equally divided into three regions (proximal, middle, and distal), and longitudinal thin sections were stained with hematoxylin and eosin (HE). The sections were observed under an optical microscope and the lengths of 30 consecutive sarcomeres each from 10 muscle fibers per muscle were measured. The coefficient of variation (CV) was calculated to assess the nonuniformity of sarcomere length. Means and CVs of sarcomere length were compared between ankle joint angles and regions, using two-way analysis of variance followed by the Bonferroni post hoc test, with a significance level of 0.05.
RESULTS:
There were significant differences in sarcomere lengths in each region between the 40 and 110 degree ankle joint angles and between the 40 and 180 degree joint angles, but no significant differences between the 110 and 180 degree joint angles. The CV tended to be highest for the 40 degree ankle joint angle.
CONCLUSION:
In the rat TA muscle, the degree of change in sarcomere length when the ankle joint angle is changed and the skeletal muscle is stretched or shortened differs, implying that sarcomere nonuniformity is greater when the muscle is shortened. These findings may underlie the mechanisms of muscle injury and provide clues to effective methods of protection against it.