Question

Which contractile result of rate-coding (i.e., frequency of activation) will produce the most force?

Select one:

a. twitch

b. summation

c. tetanus

d. all of the above produce the same amount of force

Answer 1

c. tetanus

Explanation; FACTORS THAT INFLUENCE THE FORCE OF MUSCLE CONTRACTION:

Multiple-motor unit summation or recruitment:All of the motor units in a muscle usually don't fire at the same time. One way to increase the amount of force generated is to increase the number of motor units that are firing at a given time. We can say that more motor units are being recruited. The greater the load we are trying to move the more motor units that are activated. However, even when generating the maximum force possible, we are only able to use about 1/3 of our total motor units at one time. Normally they will fire asynchronously in an effort to generate maximum force and prevent the muscles from becoming fatigued. As fibers begin to fatigue they are replaced by others in order to maintain the force. There are times, however, when under extreme circumstances we are able to recruit even more motor units.

Wave summation: a muscle twitch can last up to 100 ms and that an action potential lasts only 1-2 ms. Also, with the muscle twitch, there is not refractory period so it can be re-stimulated at any time. If you were to stimulate a single motor unit with progressively higher frequencies of action potentials you would observe a gradual increase in the force generated by that muscle. This phenomenon is called wave summation. Eventually the frequency of action potentials would be so high that there would be no time for the muscle to relax between the successive stimuli and it would remain totally contracted, a condition called tetanus. Essentially, with the high frequency of action potentials there isn't time to remove calcium from the cytosol. Maximal force, then, is generated with maximum recruitment and an action potential frequency sufficient to result in tetanus.