Exploring the Relationship Between Heart Rate Variability (HRV), Training Load, and Endurance Performance

Inclusion Criteria: Actively participating in cardiovascular training (3-5 days/week). Able to run a 5K (3.1 miles) distance at a self-selected location, three times over 8 weeks. Age 18-65 years. Subject is willing to refrain from vigorous exercise (light physical activity only) 24 hours prior to timed 5K assessment. Subject is willing to avoid alcohol consumption 24 hours prior to 5K assessment. Subject is willing to provide consent. Subject is able to continuously wear their activity tracker, including during sleep, except when submerged underwater (i.e., swimming, bathing). Subjects must have compatible wearable device (Android, Apple Health, Dexcom, Fitbit, Garmin, Health Connect, Oura, Polar, Whoop, and Withings). Exclusion Criteria: Individual has a condition the Investigator believes would interfere with his ability to provide informed consent, comply with the project/study protocol, which might confound the interpretation of the project/study results or put the person at undue risk. Those with a medical history that would interfere with the results of this study. Those that have ≥1 risk factor for cardiovascular disease according to the American College of Sports Medicine. Age: Men ≥ 45 yrs; Women ≥ 55 yrs. Family History: Heart attack, "bypass surgery", or sudden death before the age of 55 yrs for father/brother, or before 65 yrs for mother/sister. Cigarette Smoking: Current smoker, or have quit \< 6 months, or exposed to environmental smoke. Sedentary lifestyle: Not participating in moderate (sweating) physical activity at least 3 days/week for 3-months. Obesity: Body mass index ≥ 30 kg/m2 or waist girth 102 cm (40 inches) for men and 88 cm (35 inches) for women. Hypertension: Systolic Blood Pressure ≥ 140 mmHg and/or Diastolic ≥90 mmHg, or taking medication. Dyslipidemia: LDL ≥130 mg/dl, or HDL \< 40 mg/dl, or taking medication. Or triglycerides (TG) \> 200 \> mg/dl. Pre-diabetes: Impaired fasting glucose (IFG) ≥ 100 mg/dl or oral glucose tolerance test (OGTT) ≥ 140 or ≤ 199 mg/dl confirmed by two different measurements. Under the care of a physician. Sleep disorders. Using prescription medications that would impact sleep. If female, you are not pregnant, planning to get pregnant or currently breast feeding. Not able to wear activity tracker continuously. Lack of proficiency in English. Lack of proficiency or access to the internet and email address. Participation in another clinical trial within the past 30 days. Subject is employed by, or has a parent, guardian, or other immediate family member employed by a company that manufactures any products that compete with any Gatorade product. If subject is unsure if a company would be considered a competitor to Gatorade, they will be asked to please let the study investigator know the name of the other company and the nature of their relationship to that company before they sign the informed consent.