Inclusion Criteria

- INCLUSION CRITERIA:

To be included, participants must meet the following:

- Healthy, 18 years of age or older;

- Speak and understand the English language.

EXCLUSION CRITERIA:

Participants with any one of the following will be excluded:

- Inability to provide informed consent for the study;

- Are unwilling or unable to cooperate with the study procedures or travel to NIH for
the procedures;

- Have a confirmed medical condition causing clinically significant fatigue symptom
(e.g. congestive heart failure, cancer actively receiving therapy, sleep disorders);

- Currently taking medications that cause fatigue (e.g. diuretics, beta blockers,
narcotics);

- Working late evening and night shifts within the past month;

- Have severe psychiatric conditions (e.g. major depressive disorder, bipolar disorder,
anxiety disorder, schizophrenia, drug and/or addiction abuse or dependence);

- Report consuming more than 300mg of caffeine containing beverages (approximately 4
cups of coffee or 8 cups of soda or tea) or food (approximately 1 lb of chocolate)
within 24 hours;

- Reports consuming more than 2 servings of alcohol containing beverages every day and
with detectable blood alcohol content (BAC) using breath analyzer (greater than 1
mg/dL of BAC);

- Pregnant or lactating women.

- Unable to refrain from smoking at least 4 hours prior to exercise testing sessions

- Any medical condition that limits exercise performance (e.g. any condition with a
ventilatory limitation during maximal exercise)

- Any medical condition that affects participants' safety with exercise (e.g.: severe
heart disease, uncontrolled diabetes)