On contraction of the muscles, marked changes in X-ray reflections are observed, suggesting that conformational changes of contractile molecules and the movement of myosin heads during muscle contraction. Time slice requires tension peak after the onset of stimulation and the height of tension peak depends on the number of twitch cycle. The muscles were stimulated by five successive stimuli at an interval of 80 ms started while the tension was still being exerted by the muscles. The intensity of I11, I10, 143a and 215a reflection measured with 5ms time resolution and is recorded in isometric tension. The peak height of I11 and 143a intensity is changed after the onset of a stimulation Ii, and the length of twitch is shortened by successive twitches in the case of stimulation Ti. On the other hand, the peak height of In and 215a intensity starts to decrease at the 1st twitch and remains constant at low peak height without appreciable recovery during the contraction term. In the case of successive twitch stimulation, the myosin heads of muscle are once moved from their resting position and never returned to their initial position.