The Effect of Prior Muscle Activation on the Compound Muscle Action Potential (CMAP)

The purpose of this investigator-initiated study is to determine the effect of prior muscle activation on the response obtained by nerve conduction studies (the compound muscle action potential \[CMAP\]) looking at the amplitude, area, and duration of the CMAP and evaluating the length of time the CMAP is larger than at baseline. On the opposite side, the corresponding CMAP will be tested periodically, but there will be no muscle activation on that side.

Null Hypothesis: While controlling all possible technical and other known physiological variables, prior activation of a muscle has no effect on the amplitude and area of the compound muscle action potential (CMAP); and the CMAP does not change over time in the relaxed muscle (on the opposite side).

The investigators suspect that there is an effect of prior activation of the muscle on the subsequent CMAP recorded from that muscle.

Nerve conduction studies (NCS) will be performed with supramaximal nerve stimulation, surface stimulation, surface recording, and with best possible technique controlling as many variables as possible including the location of the recording electrodes and with a warm muscle and nerve (measuring temperature at the skin) in each of 3 "arms" of the study:

* ulnar nerve stimulation at the wrist recording from the hypothenar eminence,
* median nerve stimulation at the wrist recording from the thenar eminence, and
* peroneal nerve stimulation at the ankle recording from the extensor digitorum brevis muscle.

NCS will be performed in a rested muscle (rested for 15 minutes or longer) and then multiple times for up to 40 minutes after maximum isometric contraction (activation) of the tested muscle for a defined length of time. The defined lengths of muscle activation include:

* "a brief twitch" (activation for a fraction of a second),
* 2 seconds,
* 5 seconds,
* 10 seconds, and
* 20 seconds (two epochs of 10 seconds of activation with 1-2 seconds of rest between the two epochs).

The CMAP will be recorded multiple times from the muscle which was activated (pre-activation; as well as post-activation at multiple times after muscle activation: immediately, 5 sec, 10 sec, 15 sec, 20 sec, 30 sec, 60 sec, 90 sec, 2 minutes, and every minute up to as long as 40 minutes). Similar recordings will be made after each of the 5 durations of muscle activation ("a brief twitch," 2 seconds, 5 seconds, 10 seconds, and 20 seconds) of each of the three muscles (hypothenar, thenar, and EDB). CMAP amplitude (baseline to negative peak), area (under the negative curve), and duration (of the negative CMAP) will each be measured at each timepoint; and skin temperature in the region of the "active" recording electrode will be measured. Each data type will be compared over time in a series, identified as muscle from which recorded, duration of muscle activation performed prior to the recording, and time after the end of muscle activation.

On a few occasions during the testing of the CMAP on the side on which the muscle is activated, there will be recording of the CMAP from the corresponding muscle on the opposite side, but that second side will be relaxed the entire time of testing (for 4-5 hours).

If the CMAP changes more than a small amount on either side, F waves may be tested while the muscle is at rest.

Each subject will participate in each of the 3 "arms." Testing for the five series of recordings from each muscle is anticipated to take 4-5 hours, i.e., after screening, 12-15 hours total for testing the 3 muscles in each subject.

Eligibility Criteria:
Inclusion Criteria:

* Normal, healthy volunteers
* Age 18-49

Exclusion Criteria:

* Localized or generalized neuromuscular disorder
* History of neuropathy
* History of diabetes
* History of prior injuries or surgeries of the back, neck, or limbs to be tested which in the opinion of the investigator might have the potential to influence the compound muscle action potential
* Medications other than eyedrops or non-steroidal anti-inflammatory agents (as needed) or contraceptive agents or non-steroidal topical agents
* Abnormalities by screening nerve conduction studies
* Anomalous innervation of the tested extensor digitorum brevis via screening nerve conduction studies
* Use of caffeine or nicotine within 8 hours of testing