Isometric Force Lab Report

Experiment 1 showed the isometric force generated by the ADM muscle of the test subject was able to be measured accurately and quantified into EMG activity as shown in results from Table 1. The established threshold of 2.2mA was used for subsequent increases in stimulation from the threshold to show that more motor units of both Type I and Type II were simultaneously being recruited. The size of the twitch force at 20% above the threshold, 2.6mA, was not a drastic jump as was 40%, 3.2mA, which showed considerably higher twitch force (Figure 4). This jump is primarily due to more motor neurons being activated as the stimulus intensity to the ulnar is increasing. Normally the nervous system recruits small-slow motor units first then large-fast …show more content…
Thus one would observe summation of the action potentials as the stimulus is increased due to an increase in the frequency of the firing of action potentials across multiple motor units. This is exactly what was observed in the compound action potential recordings in Figure 2, which showed that the CAP amplitude increased proportionately as the stimulus intensity increased after 20% above threshold. It is known that the force of which the muscle contracts will increase as larger motor neurons are recruited along with smaller weaker ones (Wakeling, 2005).
The resultant CAP observed in experiment 2 was due to the multiple stimuli being inserted in a span of time close enough that they were able to be summed together and recorded as such. It is also known that the resultant summated CAP twitch would be larger in amplitude than the individual muscle twitches by themselves (Celichowski, et al 2010). This behavior of the muscle fibers mimics an unfused tetanus where due to the rate of stimulation the fibers are unable to completely relax before the subsequent stimulus, or may have a partial relaxation period in between