[Accuracy of determining sarcomere lengths in contracted muscle by laser diffraction method]

The method of laser diffraction by cross-striated muscle was used to investigate changes of sarcomere lengths during contraction. The development of muscle tension was recorded simultaneously with length measurings. The changes of the sarcomere length were determined from angular displacement between the left (+1)- and right-(-1)-first order maximums. The absolute error is less than 0.65 micrometer for the sarcomere lengths 1.8--2.8 micrometers and for the lengths 2.8--3.3 micrometers it is less than 0.1 micrometer. The resolution of length changes is under 0.003 micrometer over the whole range. It was shown that not only the positions of (+1)- and (-1))-diffraction maximums were displaced, but the position of zero order diffraction maximum might be changed. We explained this phenomenon in terms of form changes of the illuminated region of the fiber.