Measurement of transverse stiffness during contraction in frog skeletal muscle using scanning laser acoustic microscope.

The change in the transverse propagation velocity was measured by the scanning laser acoustic microscope (SLAM) during contraction in living frog skeletal muscles. The images of the interferogram were processed by image-analyzer and the propagation velocity was calculated from the shift of the interference lines at rest and during contraction. In all the measurements, the velocities during contraction were clearly slower than at rest and this fact indicates that the transverse stiffness decreased during contraction. After stimulation, the beginning of the decrease in the propagation velocity preceded that of the increase in force by 30-40 ms, suggesting that the decrease in the transverse stiffness reflects the molecular mechanism of force development in muscular contraction.