Muscle And Synthesis Essay

Background of physiological context
Previously, Capaday and Stein (1986) had conducted a study which aimed at investigating the amplitude modulation of the soleus H-reflex during the step cycle of human locomotion. The walking and stance phases of locomotion were investigated. This study showed that the H-reflex during walking was modulated greater than in the stance phase. The outcome of this study concluded that there were other central neural mechanisms which modulated the amplitude of the H-reflex and it was not just the consequence of α-motor neuron excitation levels. In the current paper, Capaday and Stein investigated the modulation of the H-reflex and whether it is similar in running as it is in walking in the same subject. This investigation expected the modulation of the H-reflex to be different in the two separate locomotion types. It was said running would elicit a greater H-reflex amplitude due to the increase in impact force between the ankle and the ground. This greater H-reflex amplitude would have been required to further stiffen the ankle joint before impact. It was noted that if differences between H-reflex and e.m.g were observed between the two locomotion types this study would provide further evidence that modulation of the

H-reflex occurred due to central neural mechanisms and not just of α-motor neuron excitation levels.
Experimental approach, including techniques used and data analysis
The experimental procedure used in this study was the one conducted in the Capaday and Stein (1986) along with modifications.
The procedure involved eight human subjects who had H-reflexes of the soleus muscle recorded whilst walking at four kilometres an hour and running at eight kilometres an hour on a treadmill.

Silver electrodes were used to record the e.m.g of the soleus muscle and tibialis anterior, and stimulate the tibial nerve below the popliteal fossa. The use of the electrodes to stimulate the tibial whilst walking and running was found to be problematic, this is because the nerves distance from the electrode was continually changing, therefore altering the stimulus strength. This was eradicated by repetition at different intensities and use of the M-wave, allowing comparison of similar stimulus intensities through the locomotion

task.
The use of switch which was placed under the foot of the subject allowed the recording the e.m.g. activity of the soleus and tibialis anterior muscle during the locomotion task. The reflex response involved the switch under the foot which was connected to the computer, once the foot was flat (step mark) a stimulus mark was created and the e.m.g of the soleus was recorded. The time of inactivity between the stimulus and step mark indicated the phase of the locomotor task the stimulus occurred. The average soleus signal was obtained allowing the average H-reflex response to be gathered.
Principal findings
The paper found multiple new findings including that the H-reflex of the soleus is also modulated during running. It was found that late into the stance phase the H-reflex reached its peak amplitude, this is due to many factors, as the reflex is required to lift the body off the ground and reduce the body swaying by increasing the muscle tension. Also what was found was that during the swing phase of movement the H-reflex was absent.
Another finding which needs to be highlighted is the peak of soleus e.m.g on average is 2.4 times higher than walking, although the maximum amplitude of the H-reflex was never larger during walking. The H-reflex was significantly lower in running than it was in walking.
It was stated that there were other central neural mechanisms which modulated the amplitude of the H-reflex and it was not just the consequence of α-motor neuron excitation levels, this is due to the average difference in H-reflex maximum amplitude.