Nervous System Function in Normal Volunteers During Cycling Training
Nervous System Function in Normal Volunteers During Cycling Training
This study will identify changes that occur in the nervous system of healthy normal
 volunteers while they are learning a cycling task.

 Healthy subjects 18 years of age and older who can cycle for 16 minutes may be eligible for
 this study. Candidates will be screened with a brief medical history and physical
 examination.

 Participants will be assigned to one of three groups:

 -  Complex training: Cycling for 16 minutes at a constant speed of 60 rpm with frequent
 changes in pedal resistance.

 -  Simple training: Cycling for 16 minutes at a constant speed of 60 rpm with no changes in
 pedal resistance.

 -  No training: Remaining seated on the bike for 16 minutes performing no exercise.

 Participants will cycle for 16 minutes for the training task, plus 4 minutes before and after
 the training. Reflexes will be measured with nerve conduction studies and somatosensory
 evoked potential (SSEP) recordings before and after training. Nerve conduction studies
 measure the speed with which nerves conduct electrical impulses and the strength of the
 connection between the nerve and the muscle. For these studies, a probe is placed on the skin
 over the calf muscles and the knee to deliver a small electrical stimulus, and wires are
 taped to the skin to record the impulses. SSEP recordings, which measure of the excitability
 of the brain to sensory stimuli, are collected from electrodes placed on the scalp.

 After the training period, multiple train stimulation (MTS) is applied for 10 minutes. For
 MTS, weak electrical currents are delivered for 10 seconds every 10 seconds. These stimuli
 produce a buzzing sensation without pain, discomfort, or muscle twitching. The MTS is
 followed by another 4 minutes of cycling.

 Participants also undergo transcranial magnetic stimulation (TMS). For this procedure, an
 insulated wire coil is held over the scalp. A brief electrical current is passed through the
 coil, creating a magnetic pulse that travels through the scalp and skull and causes small
 electrical currents in the brain cortex (outer part of the brain). The stimulation may cause
 twitching in the muscles of the face, arm, or leg. The electrical activity of the muscles is
 recorded with a computer or other recording device, using electrodes attached to the skin
 with tape.
In a previous study, we have shown that locomotor training with frequent changes in pedal
 resistances (complex training) elicits significant improvement in locomotor performance
 compared to training consisting of constant pedal resistance (simple training). Behavior
 gains associated with complex training correlate with down-regulation in the excitability of
 the alpha-motoneurone pools controlling muscles involved in the training task, as measured by
 changes in the soleus H-reflex, raising the hypothesis of a cause-effect link between
 performance improvements and modulation of spinal cord function. The purpose of this protocol
 is to determine if down-regulation in the excitability of the alpha-motoneuron pool is
 required for the improvement in locomotor performance. To address this issue, we hypothesize
 that up-regulation of alpha-motoneuron excitability will cancel improvements in locomotor
 performance elicited by complex training more than in subjects undergoing a period of simple
 training. The results of this study would provide novel information on the spinal substrates
 underlying learning of a locomotor task in intact humans and could be relevant to the design
 of rehabilitative strategies in patients with locomotor disorders.
-  INCLUSION CRITERIA:

 Normal volunteers (ages 18 and above) who are willing to participate and who are considered
 able to cycle for16 minutes based on neurological and physical exams.

 EXCLUSION CRITERIA:

 1. Subjects with history of heart condition, unresponsive arterial hypertension,
 diabetes, chronic back pain, sciatica, peripheral neuropathy, rheumatoid arthritis,
 active joint deformity of arthritic origin, alcohol or drug abuse, psychiatric
 disorder requiring hospitalization or prolonged treatment, head injury with loss of
 consciousness, epilepsy.

 2. Subjects with cardiac pace-makers, intracardiac lines, or implanted medication pumps.

 3. Subjects with history of hyperthyroidism or individuals receiving drugs acting
 primarily on the central nervous system or disorders of the blood coagulation system.

 4. Subjects with eye, blood vessel, cochlear, or eye implants.

 5. Subjects with increased intracranial pressure as evaluated by clinical means.

 6. Subjects with metal in the cranium except in the mouth.

 7. Subjects with metal fragments from occupational exposure or surgical clips in or near
 the brain.

 8. Women in the last trimester of pregnancy.