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A Scientific Approach to
Optimal Performance

Optimize Performance 24 hours a day. There’s a fine line between pushing your limits and overtraining or injury. The key is appropriately balancing your Strain with your body’s Recovery. WHOOP Recovery gives you daily insights into how well your body is responding to Strain.

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Measure Strain

to ensure the load from an entire day of activity aligns with what your body can respond to.
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Measure Recovery

to optimize the activities and workouts to prepare your body for more Strain.
Day Strain
Graph of Whoop athlete data
Graph of Whoop athlete data
Graph of Whoop athlete data

Under Training

Missed opportunity to train when your body is ready to excel.

Optimal Training

The perfect balance of pushing your body to improve without burning out.

Over Training

With too much load, extra training can be more detrimental than helpful.

Highlights from the Research

  • Prevention of over training is crucial, and is possible by a systematic tracking and assessment of how the athlete is adapting to designed stress (Halson, 2014).
  • High intensity and volume without sufficient rest may lead to overtraining (Kinucan & Kravitz, 2007).
  • Daily measurements of RHR and HRV alongside exercise intensity are the foundations of a scientific approach to optimal training (Buchheit, 2014).
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Halson, S. L. (2014). Monitoring Training Load to Understand Fatigue in Athletes. Sports Med Sports Medicine, 44(S2), 139-147. doi:10.1007/s40279-014-0253-z. read research

Kinucan, P., & Kravitz, L. (2007). Overtraining. ACSM‘s Health & Fitness Journal, 11(4), 8-12. doi:10.1249/

Buchheit M (2014) Monitoring Training Status with HR Measures: Do All Roads Lead to Rome? read research


WHOOP is the first company to automatically measure your heart rate variability and resting heart rate at the optimal times each night. These measurements help to form your Recovery.

Interpreting WHOOP Recovery

WHOOP boiled down complex research into an easy-to-implement approach to understanding your body’s readiness to perform.



Green Zone

Your body is likely primed to adapt to a larger training load.



Yellow Zone

Your body can respond to training but is not peaking.



Red Zone

Consider prioritizing Recovery activities and be cautious of overtraining.

3 Main Metrics Inform Your Recovery

The measurements taken each night are considered against each individual’s rolling baseline and recent trends to create a personalized Recovery each morning.

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Resting Heart Rate (RHR)

The number of times your heart beats per minute while at rest.

WHOOP measures your RHR while your body is at complete rest during your deepest sleep each night.

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The amount of time your body spends in light, REM, and slow wave sleep.

WHOOP automatically calculates the specific sleep your body needs vs. the sleep achieved each night, providing a daily Sleep Performance.

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Heart Rate Variability (HRV)

Heart rate variability is the measure of the naturally occurring irregularity of your heartbeat. Leading exercise physiologists agree that HRV is one of the most useful tools for tracking training and setting the optimal loads that lead to improved performance (Dong, 2016).

WHOOP measures HRV during slow wave sleep and uses the metric RMSSD (Root Mean Square of Successive Differences).

HRV graph HRV graph

Highlights from the Research on HRV

  • Numerous studies have shown that RHR and HRV are powerful predictors of athletic performance (Vasterinen et al., 2011, Kiviniemi et al., 2007 and 2009, Plews et al., 2013, Uusitalo et al., 1998).
  • High HRV is usually positively correlated with athletic performance and training adaptability (Dong, 2016).
  • Modifying training intensity based on HRV fluctuations has been shown to result in better control (Kiviniemi et al, 2009).
  • WHOOP: Basketball shooting accuracy is correlated with WHOOP Recovery on game day mornings. read research
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Vesterinen V, Häkkinen K, Hynynen E, Mikkola J, Hokka L, and Nummela A (2011) Heart Rate Variability in Prediction of Individual Adaptation to Endurance Training in Recreational Endurance Runners. Scand J Med. Sports. 23:171-180. read research

Kiviniemi AM, Hautala A, Kinnumen H, Nissila J, Virtanen P, Karjalainen J, Tulppo MP (2009) Daily Exercise Prescription Based on Heart Rate Variability Among Men and Women. Med Sci Sports Exerc 41:497. read research

Plews DJ, Laursen PB, Stanley J, Kilding AE, Buchheit M (2013) Training Adaptation and Heart Rate Variability in Elite Endurance Athletes: Opening the Door to Effective Monitoring. Sports Med. 43:773-781. read research

Dong, J. (2016). The role of heart rate variability in sports physiology (Review). Experimental and Therapeutic Medicine Exp Ther Med. doi:10.3892/etm.2016.3104. read research


WHOOP Strain is an objective and consistent measure of cardiovascular strain. Simply put, it is a summary measurement of the exertion placed on your cardiovascular system in a given day.

Strain categorization key

Day Strain

Practice and workouts are just one piece of the full picture when it comes to Strain. Since WHOOP is always on, every heartbeat counts. All your heart rate data from the moment you wake up to the moment you go to bed results in your overall Day Strain.

Developing a Strain Scale

WHOOP’s Strain scale takes its roots from the Borg Scale of Perceived Exertion. WHOOP conducted over 1,500 of hours of workouts with hundreds of athletes, correlating rates of perceived exertion with cardiovascular load. Today, WHOOP is able to supplement an athlete’s rate of perceived exertion with an objective calculation for the Strain put on their body.

In order to develop a single Strain scale that is equally applicable for a day in the office or an ultra marathon, WHOOP’s Strain scale becomes progressively more difficult to achieve higher Strain.

Strain categorization key

How to Use WHOOP Strain

The Day Strain is a tool for understanding how your body is responding to all the demands of daily life.

Performing the same training load and acquiring a lower Strain is an indication of improving fitness because it required less total exertion to achieve the same output.

Highlights from the Research

  • Perceptual effort ratings can complement physiological measurements of physical performance and work capacity (Borg, 1982).
  • It is important to understand the optimal training load at which adaptation occurs without raising the risk of injury (Owen, 2015).
  • WHOOP: An objective and consistent Strain metric provides an actionable and reliable option for measuring physical exertion in athletes. read research
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Borg G.A. Psychophysical bases of perceived exertion. Medicine and Science in Sports and Exercise. 1982; 14:377-381. read research

Owen AL1, Forsyth JJ, Wong del P, Dellal A, Connelly SP, Chamari K. Heart rate-based training intensity and its impact on injury incidence among elite-level professional soccer players. 2015; 1705-12. read research


As an athlete, your body withstands high loads of physical stress on a regular basis. Science has yet to develop a better way to repair, regenerate, and prime your body for peak performance than Sleep (Samuels, 2008).

WHOOP Approach to Measuring Sleep

The WHOOP Strap and the sleep algorithms have been calibrated to polysomnography (PSG) based on sleep studies across age, gender, and fitness levels in a sleep laboratory.

Graph of a Whoop user's sleep over a night Pie chart of a Whoop user's sleep phases

WHOOP Measurements While You Sleep

  • Clock icon Time in Bed - The total amount of time dedicated to sleep.
  • Moon icon Hours of Sleep - Indicates the amount of restful sleep you got.
  • Warning icon Disturbances - Brief disruptions of sleep (3-7 per hour) are normal. They are typically too short to remember the next morning. Frequent disturbances are associated with low quality sleep.
  • Sleep latency icon Latency - The amount of time that it takes to fall asleep. Short latency (<10 minutes) could suggest sleep debt.
  • Sleep cycle icon Sleep Cycle - Sleep progresses in four stages: Light, Rapid Eye Movement (REM), Slow-Wave Sleep (SWS), and Awake. A healthy night of sleep typically includes 3-5 complete cycles.

WHOOP Measurements While You're Awake

In addition to measuring Sleep, WHOOP measures how much sleep you need each night by tracking:

  • Clock iconBaseline Amount of Sleep
  • Strain iconToday’s Strain
  • Sleep debt iconSleep Debt
  • Nap iconToday’s Naps
Phone running Whoop app displaying reccomended sleep needs Phone running Whoop app displaying reccomended sleep needs

Highlights from the Research

  • Improvements in specific measures of basketball performance after sleep extension indicate that optimal sleep is likely beneficial in reaching peak athletic performance (Mah et al., 2011).
  • Chronic sleep debt has been correlated with a 68% greater risk of sport-related injury over the course of a 21-month period when compared to athletes with similar training loads getting adequate sleep (Milewski et al., 2014).
  • Sleep debt decreases your body’s ability to regulate temperature, so you sweat less and burn out faster in workouts (Sawka et al., 1984).
  • WHOOP: Data demonstrates that both time spent asleep and time spent in REM sleep are positively correlated with performance. read research
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Samuels C (2008) Sleep, Recovery, and Performance: The New Frontier in High-Performance Athletics. Neurol Clin. 26:169-180. read research

Mah, C. D., Mah, K. E., Kezirian, E. J., & Dement, W. C. (2011). The Effects of Sleep Extension on the Athletic Performance of Collegiate Basketball Players. Sleep, 34(07), 943-950. doi:10.5665/sleep.1132. read research

Milewski M, Skaggs D, Bishop G, Pace J, Ibrahim D, Wren T, Barzdukas A (2014) Chronic Lack of Sleep is Associated with Increased Sports Injuries in Adolescent Athletes. J Pediatric Orthopedics 34: 129-33.

Sawka MN, Gonzalez RR, Pandolf KB (1984) Effects of Sleep Deprivation on Thermoregulation During Exercise. Am J Physiol Regul Intgr Comp Physiol 246:R72- R77. read research