. Biophysical science. Biophysics. 142 Muscles /8 : 3 If one stimulates an excised muscle by means of an electrical shock (or a mechanical impulse, or heat, cold, and so on), a twitch occurs. If the stimuli are spaced a long time apart, the muscle relaxes to its original ⬠r "J/-A Is, § 5 5% Length of Twitch Varies with Particular Muscle, Temperature, and pti I _L_L_LJ_i_+ 1 25 |xsec f/\ r\ /v^!. Time (a) Time (b) AL/L Tetany Fatigue sec ' * â Time (c) Figure 3. Curves of contraction, (a) Occasional stimulation shows twitches. Arrows indicate stimuli, (b) Frequent stimulation leads to s
. Biophysical science. Biophysics. 142 Muscles /8 : 3 If one stimulates an excised muscle by means of an electrical shock (or a mechanical impulse, or heat, cold, and so on), a twitch occurs. If the stimuli are spaced a long time apart, the muscle relaxes to its original ⬠r "J/-A Is, § 5 5% Length of Twitch Varies with Particular Muscle, Temperature, and pti I _L_L_LJ_i_+ 1 25 |xsec f/\ r\ /v^!. Time (a) Time (b) AL/L Tetany Fatigue sec ' * â Time (c) Figure 3. Curves of contraction, (a) Occasional stimulation shows twitches. Arrows indicate stimuli, (b) Frequent stimulation leads to summation, (c) Prolonged tetany leads to fatigue. Note the difference in the time scale as compared to (a) and (b). After S. Cooper and J. C. Eccles, J. Physiol. 69:377 (1930). length between twitches, and a contraction curve is obtained of the shape shown in Figure 3a, for isotonic contractions. If the stimulus is repeated before relaxation occurs, summation is observed as shown in Figure 3b. With still more rapidly repeated stimulation, a smooth contraction curve results such as shown in Figure 3c. The steady con- traction is called tetany. All muscles will eventually fatigue and fail to contract, even though stimulated. This type of fatigue probably never occurs in the healthy intact animal, as the nervous system undergoes fatigue before the muscles do. Curves illustrating the strength of isometric and isotonic contractions are shown in Figures 4a and 4b, in terms of effect of length on tension developed in isometric contraction and of load on shortening produced during isotonic contraction. Only in isotonic contraction is work done. It is easy to show that the maximum work is done at half the maximum load for muscles for which the straight line relationship of Figure 4a is valid. The straight line can be described by. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of
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