Measurement of sarcomere length in situ

The laser diffraction method was applied to a whole, unisolated muscle of the mouse in order to study the changes in sarcomere length caused by passive movements of joints. The accuracy of measurement of sarcomere lengths in situ by this method was +/- 5.6%. The site-to-site variation in sarcomere length within resting muscle was not affected by stretching of the muscle and the sarcomere length varied in direct proportion to the muscle length (correlation coefficient = 0.805, p less than 0.01). These results agreed with previous observations on resting muscles in vitro.