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How Does WHOOP Strain Work?


How Does WHOOP Strain Work?

Strain 101: Everything you want to know about how WHOOP quantifies the workload your body takes on.

Below we’ll discuss exactly what our strain metric is, how it’s calculated, factors that play into determining your strain for a whole day and for various activities, WHOOP averages for each, as well as the relationship between strain and recovery.  

What is WHOOP Strain?

WHOOP Strain is a measure of cardiovascular and muscular exertion that quantifies the amount of physical and mental stress you’re putting on your body. We track your strain on a 0-21 scale, both for your entire day and for specific workouts and activities. Inspired by Borg’s Rating of Perceived Exertion, strain numbers can be loosely broken down as follows:

whoop strain scale 0-21
WHOOP measures your strain on a 0-21 scale. the higher it gets the harder it is to build more.

LIGHT (0-9): Minimal stress put on the body, room for active recovery MODERATE (10-13): Moderate stress on the body, generally good for maintaining fitness HIGH (14-17): Increased stress and activity level, ideal for making fitness gains when training ALL OUT (18-21): Significant stress, often overreaching, likely very difficult to recover from the next day Learn More: Why WHOOP Doesn't Count Steps  

What Causes Strain & How Does WHOOP Calculate It?

WHOOP measures strain based on cardiovascular load and muscular load. Cardiovascular being your heart rate, and the higher your HR gets and the longer it stays elevated, the more strain you accumulate. When you use Strength Trainer, WHOOP can track your weights, reps, and sets to understand the demands you are putting on your musculoskeletal system. Muscular load measures movement and its underlying physics using the accelerometer and gyroscope sensors in WHOOP, and combines these signals with advanced biomechanics and mathematics.

Cardiovascular load is automatically calculated using the advanced sensors in your WHOOP device. The higher your heart rate, the higher your strain will be. Muscular load is factored into your strain score in two ways:

  1. When you complete a workout using Strength Trainer, WHOOP will track your weights, reps, and sets to calculate the demands you are putting on your musculoskeletal system. Your Strain Score will then include both a cardiovascular and muscular load percentage. 
  2. With research coming out of several WHOOP Labs studies, WHOOP automatically calculates the muscular and cardiovascular load of select activities including yoga, Pilates, and barre. Your Strain Score for these activities will also include both a cardiovascular and muscular load percentage. 

Most wearables only track your cardiovascular load during exercise using your heart rate, which is great for exercises like running or cycling, but doesn’t capture the full picture for low impact activities like these that make your muscles work hard.

The metric muscular load includes both volume and intensity components.

  • Volume is measured similarly to traditional volume load, but it incorporates effective mass. It takes into account your body mass, but only includes the parts of your body that are moving and doing the work. For example, a full body exercise like a squat or clean and jerk will have more muscular load than a bench press.
  • Intensity quantifies how much effort or exertion you are giving to complete the lift. This includes the speed of the movement and the proximity to failure, or the fatigue profile of the set.

WHOOP then calculates the cardiovascular and muscular load to give you one complete Strain score. Regular daily activities like work, commuting, running errands, and parenting may all cause strain. So can stress, anxiety, excitement, or feeling nervous–even being a sports fan is strenuous.

whoop app strain screen

WHOOP calculates your strain for the entire day, and for specific periods of exercise or activity. Learn More: FAQs About WHOOP Strain  

Activity Strain vs. Day Strain

When WHOOP notices a spike in heart rate and movement for a sustained period of time, it will automatically detect your activity or workout and give you a strain value for it (you can also add other activities manually and see their strain). Your total day strain provides you with additional insight into the cardiovascular load your body takes on outside of exercise. For example, a presentation at work or a busy afternoon with the kids might raise your day strain above average, even on a day you don’t work out.

activity strain vs day strain

WHOOP detects your workouts and tells you how strenuous they are. Your day strain is not the sum of your activities.

If you have multiple workouts in a day, the strain of your activities does not add up to your total day strain. The WHOOP strain algorithm is logarithmic, meaning the higher your strain gets the harder it becomes to build more. As illustrated by the top graphic above, it is much easier to go from a 0 to 10 strain than it is to go from a 10 to 20. Hypothetically, running a marathon might lift your day strain to 20.4 or 20.5, but then running a second one that day could only increase it to 20.6 or 20.7. Learn More: The Science of Strain with Dr. Andy Walshe Podcast  

What is a “normal” amount of strain?

The strain average for all WHOOP members is right around 11.0 per day. To no surprise, the number tends to decrease with age. Below you can see what daily average strains are by age and gender:

The average daily strain for WHOOP members is about 11.0, It decreases with age.

When it comes to individual workouts, more intense aerobic exercise leads to higher strain than less intense activity. The average strain for 1 hour of running is roughly 12.0, while an hour of walking is about 6.5. The average strain for 1 hour of functional fitness is 10.1.* *Note this data does not include Strain scores from activities like weightlifting, which will now be possible with Strength Trainer. Learn More: Average Strain of 10 Most Popular Activities  

Strain is Highly Individualized

Strain is calculated from your personal HR metrics and accounts for your individual fitness level. Since it quantifies how hard your body works and not what your body does, two people who complete the same activity may have very different strains. For example, a 90-minute hike that registers a 10 or 11 strain for the average person might be just a 5 or 6 for a highly conditioned athlete. Along the same lines, as your fitness improves you’ll start to see lower strains for that same activity. Learn More: Quantifying the Strain of NFL Football with Patrick Mahomes’ WHOOP Data  

Strain & Recovery

The higher your recovery is, the more strain your body is ready to take on.

Recovery determines WHOOP strain recommendations

The amount of strain your body is ready to handle is dictated by your recovery each day.

You may notice strain accumulate faster on days when you have a low recovery, because your body is not as prepared to handle it. A workout routine that usually gives you a 9.5 might be a 10.5 when you’re in the red. Strain Target suggests an optimal amount for you to take on each day based on your recovery. It’s a recommended level of strain intended to let you maintain fitness and still adequately recover the following day.

WHOOP recovery and strain balance

Your Weekly Performance Assessments show the balance between your Strain and Recovery. If you go above this amount you are “overreaching” (good for making fitness gains, but likely detrimental to your next-day recovery), and if you stay below it you are “restoring.” In turn, the amount of strain you take on today then affects what your recovery will be tomorrow. Learn More: Understanding WHOOP Strain Podcast