Individual Sarcomere Lengths in Whole Muscle Fibers and Optimal Fiber Length Computation

Abstract

Estimation of muscle fiber optimum length is typically accomplished using either laser diffraction or by counting the number of sarcomeres in a portion of the muscle fiber, measuring the distance that encompasses those sarcomeres and dividing by the number of sarcomeres to obtain an average sarcomere length. If the sarcomeres are not uniformly distributed, either of these techniques could produce errors when estimating optimum lengths. The purposes of this study were: to describe new software that automatically analyzes digital images of skeletal muscle fibers to measure individual sarcomere lengths; and to use this software to measure individual sarcomere lengths along complete muscle fibers to examine the influence of computing whole muscle fiber properties from portions of the fiber. Six complete muscle fibers were imaged using a digital camera attached to a microscope. The images were then processed to achieve the best resolution possible, individual sarcomeres along the image were detected, and each individual sarcomere length was measured. The software accuracy was compared with that of manual measurement and was found to be as accurate. In addition, the time to measure individual sarcomere lengths was greatly reduced using the software compared with manual measurement. The arrangement of individual sarcomere lengths demonstrated long-range correlations, which indicates problems in assuming only a portion of a fiber can be used to determine whole fiber properties. This study has provided evidence on the number of sarcomeres which must be analyzed to infer the properties of whole muscles.