How Does WHOOP Calculate Strain?
WHOOP Strain measures the cardiovascular and muscular exertion you experience throughout the day. It quantifies your body's total physical and mental stress, providing a holistic view of your daily strain.
In this article, we'll explore WHOOP Strain, explaining what it measures, how it's calculated, and how you can interpret your Strain scores to optimize your training and recovery.
- Composite Metric: WHOOP Strain combines heart rate and physical movement data to measure overall body stress, which is scored on a scale of 0 to 21 based on the intensity and duration of exertion.
- Personalized Scaling: Strain is tailored to individual fitness levels and maximum heart rate, making it adaptive as fitness improves.
- Holistic View: WHOOP provides a holistic view of physical and mental exertion by distinguishing between daily cumulative stress (Day Strain) and specific workout-related stress (Activity Strain).
- Multi-factor Influence: Recovery status, lifestyle choices (e.g., stress, hydration, diet), and fitness level affect Strain, highlighting the need to balance exertion and recovery.
How Does WHOOP Calculate Strain?
WHOOP calculates Strain using a proprietary algorithm that considers cardiovascular and muscular load. This approach provides a more accurate picture of the total stress placed on your body.
Strain is scored on a scale from 0 to 21, based on the Borg Scale of Perceived Exertion. This scale was initially developed to allow individuals to subjectively rate their exertion levels during physical activity. WHOOP takes this concept further by calculating Strain based on your heart rate and movement data.
A Strain score of 0 indicates no exertion, while a score of 21 represents maximal exertion. Most users’ Strain scores fall somewhere in the middle of this range, depending on the intensity and duration of their daily activities.
Cardiovascular Load
Measures time spent in elevated heart rate zones. The higher and longer the elevation, the more Strain accumulated as your heart pumps harder to supply muscles.
Muscular Load
Uses accelerometer and gyroscope sensors to track movement and forces exerted by muscles during physical work, incorporating both volume and intensity.
The Complexity of Load
The relationship between heart rate and Strain isn't linear. WHOOP uses a weighted calculation emphasizing time spent in higher heart rate zones. For example, 30 minutes at 80% of your max heart rate will contribute significantly more to your overall Strain than 30 minutes at 50%, even though the durations are identical.
Individual Baseline
Strain is highly personalized. It's calculated relative to your max heart rate and overall fitness level. This means the same heart rate of 150 BPM could represent a Strain of 12 for one person and 18 for another. As your fitness improves, you need to work harder to reach the same levels, allowing you to quantify progress over time.
Factors That Affect WHOOP Strain
Your daily Strain score isn't just a reflection of your workouts. It's influenced by various internal and external factors that can help you interpret data more effectively.
When you're under-recovered, your body has to work harder to achieve the same results. An activity that normally generates a 10 might bump to a 13 when you're in the red recovery zone.
Stress, diet, hydration, and alcohol consumption impact how your body responds to exertion. Illness and injury already place the body under stress, increasing accumulated Strain for any activity.
As your fitness improves, your Strain scores decrease for the same activities. This is a sign that your body is adapting and getting stronger and more efficient.
How to Interpret Your WHOOP Strain Score
Your WHOOP Strain score provides a wealth of information about your daily physical and mental stress. However, to get the most out of this data, it's important to understand how Strain is accumulated and reported.
Day Strain vs Activity Strain
WHOOP tracks your Stress in two ways: Day Stress and Activity Stress. Day Stress starts accumulating at midnight and includes all daily stressors—from work meetings to social outings. Activity Strain is specific to logged workouts. These individual bouts of exertion aggregate into your total Day Strain.
Non-Linear Strain Accumulation
The Strain scale is logarithmic. Going from a 10 to 11 requires more effort than going from 5 to 6. Consequently, a Strain of 10 and a Strain of 5 do not simply add up to 15.
Your Strain cycle begins when you go to sleep and resets the next time you sleep. If you do a late-night workout spanning midnight, it still contributes to the current Strain cycle until you rest. Remember, Strain is most helpful when used alongside your Recovery and Sleep data.
What is a "Normal" Amount of Strain?
The average daily Strain is around 11, but this number tends to decrease with age. Typical activity benchmarks include:
Running (1 hr)
Average Strain: 12.0
Functional Fitness
Average Strain: 10.1
Rather than comparing your Strain to others, focus on your baseline. If your Strain is consistently low, you may need to push harder to see fitness gains; if it's consistently high, give your body adequate time to recover.
How Can WHOOP Strain Data Enhance Wearable Clinical Trials?
Integrating WHOOP Strain data into wearable clinical trials can give researchers valuable insights into participant exertion levels. This facilitates a more holistic understanding of how interventions or disease progression may affect physical stress.
This data helps safeguard participant safety by ensuring individuals maintain appropriate strain levels during trial activities. When combined with other metrics like recovery, it provides a multidimensional view of physiological responses.
However, it's vital to consider the pros and cons of using wearables for clinical trials. Researchers must weigh factors like accuracy and compliance when deciding how to incorporate wearable data into their study designs.
Integrating WHOOP Strain into Your Clinical Trial Design
When designing a trial, it's critical to understand the calculation factors to interpret the data accurately. Consider how Strain data can contribute to your specific research questions, such as monitoring the intensity of a new exercise intervention.
Consistent wear is crucial for reliable data. Combining Strain data with recovery and sleep markers paints a complete picture of participants' overall health and response to the intervention.
Reputable Health offers expertise in integrating wearable technology, like WHOOP, into clinical trials to provide comprehensive insights into participant exertion and recovery. Leverage our platform to drive data-rich studies.