This is a double blind observational analysis of changes in heart rate variability using PD2i analyser in competitive athletes during strenuous exercise and competition.

Inclusion Criteria:

• Age >18 years, as determined by birth date given on participation form.
• Actively involved in competitive athletics
• Able to give informed consent

Exclusion Criteria:

• Any known prior autonomic dysfunction
• History of seizures or taking anti-seizure medication
• Known learning disability or attention deficit disorder
• Chronic heart conditions such as arrhythmias or valvular disease
• History of diabetes mellitus
• Taking any prescription stimulants such as Ritalin, Focalin, etc.
• Use of any performance-enhancing drugs
• Any deviation from normal found on the pre-participation physical exam such as the presence of a murmur or hypertension.

College athletes on competitive teams.