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Your WHOOP Strain Score, Explained
How to interpret Strain and use your Strain Coach effectively
Strain is one of the three measurements WHOOP provides daily, but it measures very specific things, and interpreting Strain isn’t always easy. Here’s a primer on this all-important metric, so you can interpret it more accurately and meet your goals.
What is Strain?
Strain isn’t capturing all of the ways you might move or tire your body during a workout. It doesn’t track or reflect muscle soreness or injury–at least not directly. Strain measures cardiovascular exertion; how hard your heart is working as the result of your workouts, general activity, and stress. It’s a way to quantify the amount of physical and mental stress you’re putting on your body, as measured through your cardiovascular system. According to WHOOP, here is a general range of Strain levels on a scale of 0 – 21.
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
Strain only measures how hard your heart is working, and for how long. That’s why a heavy and exhausting weightlifting workout (with few sets and lots of rest) may not accumulate much strain, but an easy paddleboard session lights your Strain up. It’s also based on how long you spend in elevated heart rate zones, so a HIIT workout (with short periods of very hard work followed by periods of rest) may not register as high Strain either.
Strain doesn’t just capture what you do in the gym. Anything that raises your heart rate, whether it’s work around the house, packing for a trip, or feeling stressed about work, can also accumulate strain, or even register as an activity on your WHOOP. (Almost every time I go shopping for clothes, WHOOP thinks I’m running a 5K.)
What affects Strain?
A 5-mile run today won’t likely bring the exact same Strain score as a 5-mile run tomorrow. That’s because a variety of factors play into how hard your heart is working at any given moment. If you’re under-recovered, ill, or seriously stressed, you’ll likely find “easy” activities can crank your Strain up. I’ve had book tour days when I don’t work out at all, but lack of sleep and the stress of lots of media has me in a 17-range for the day. If I wake up in the green with a super-high HRV, though, even a 10-mile hike at elevation won’t bump my Strain beyond a 14 or 15. The more prepared you are to take on Strain, the harder you’ll have to work to see that Strain number climb.
Your WHOOP can also automatically track activity and give you a Strain score just for that session, but only if your activity gets your heart rate high enough for a sustained period of time. Your heart rate needs to be elevated for at least 15 minutes straight for WHOOP to pick it up. (You can always start an activity manually to see the score your hot yoga class or HIIT session gives you.)
Also, the higher your Strain for the day, the harder it is to accumulate more. It’s pretty easy to get from a 5 to a 10 Strain for the day, but going from an 18 to a 19 is really hard.
What is WHOOP’s Strain Coach?
By clicking on “Strain” at the top of your WHOOP home screen, you’ll see the total Strain you’ve accumulated so far for the day, and a coaching cue below to help you interpret the data. When you click “Start Activity,” you’ll see a toggle to turn Strain Coach on. Strain Coach tells you the optimal amount of Strain you’d want to generate for that activity based on your activity levels, such that you don’t over-train. When Strain Coach is activated, WHOOP tracks your activity and sends a buzzing alert to your band to let you know when you’ve reached your target Strain for the day. (I can’t tell you how many times I’ve felt that alarm go off two miles into a ten mile hike. Oops.)
Strain Coach is another way WHOOP can help you interpret your recovery score, where you are in your menstrual cycle (if appropriate), and accumulated Strain for the day, and provide you with guidance to keep your training session balanced.
WHOOP Strain FAQ
Q: Why do I wake up with strain?
A: Your Strain count resets when you go to sleep. Because you’re burning calories and expending some energy overnight, it’s normal to wake up with a few points of Strain already registered.
Q: Why doesn’t my strain add up? If I wake up with a 4.0, then do an activity that’s a 10.0, shouldn’t my strain be 14.0?
A: Strain isn’t linear; think of it like a percentage. If you walk for 30 minutes at 50% intensity, then run for 30 minutes at 70% intensity, you’re not giving 120% effort that day. Doing an activity with a 10.0 score will increase your strain for the day, but not by 10 full points. Remember the difference between an activity Strain (which only gives you a score for that discrete period of time), and your daily Strain, which is the accumulation of your whole day–exercise session, work around the house, playing with your kid, walks with the dog, and stress levels.
Q: Why is it easy to accumulate strain some days, but harder on others?
A: It depends on your recovery, for one. If you’re in the green, you’ll need to work harder and longer to get your Strain up. If you’re deep in the red, even small amounts of activity or stress can deplete your system, leading to higher strain scores. If you have Menstrual Cycle Coaching turned on, that also factors in, as your tolerance for Strain varies with your cycle. (Watch MU x WHOOP’s Instagram Live on the subject, coming Monday 11/28.)
Q: I worked my butt off in the gym today, but my Strain score following was super low! What gives?
A: I myself have been personally victimized by my Strain score. Remember, Strain only measures cardiovascular strain. If your session involved weightlifting, HIIT with rest periods, or yoga, you may not have been breathing hard enough for long enough for significant Strain to register. (Your recovery status also factors in; weightlifting never registers as Strain for me unless I’m deep in the red.)
Q: What are average Strain scores?
A: Much like you shouldn’t compare your HRV to someone else’s, it’s also not that helpful to compare your Strain to other people’s. What’s important is using your WHOOP Strain, Recovery, and Sleep scores to help you plan your training and recovery practices. On average, WHOOP says the average daily Strain for members is around 11, but it decreases with age. You can expect one hour of CrossFit to register around a 10 for that activity, while an hour of running is around a 12, and walking just a 6.
Q: Should I aim to increase my daily average Strain?
A: That depends on your goals. If you’re a weightlifter, there may not be benefit in adding enough cardiovascular work to your training sessions to make a significant increase in your daily Strain score. If you’re already super stressed and under-recovered, the last thing you want is to purposefully try to increase Strain–you should be recovering. What you’ll notice is that as fitness improves over time, the same workout will generate a lower Strain score. That’s not a bad thing! It means your body can handle the same amount of work with less effort. What you can do, though, is keep an eye on Strain to see all of the ways your activities outside of your workout impact your cardiovascular system. I find an hour of cleaning or tidying can give me a nice little bump in Strain, adding to my fitness levels without pushing me into overtraining