Affiliate & partner disclosure: This article contains affiliate and referral links. My WHOOP link is a member referral link: you get a free WHOOP and one month free when you join, and I get free membership time. Hume Health and PerfectAmino links are affiliate links. As an authorised LifeWave Brand Partner, I have a financial interest in promoting LifeWave products. Full disclosure at the end.
A note before we start. This is general information, not medical advice. If you’re new to lifting or have a heart condition, check with your GP before starting hard training.
LifeWave X39 is a non-transdermal, general-wellness phototherapy patch that gently stimulates the skin with light to support the body’s natural energy flow for strength and stamina. It is not a treatment for any condition.
Strain is the other half of WHOOP. Recovery tells you what you’ve got in the tank. Strain tells you how much you spent.
For runners and cyclists it’s excellent. For lifters, it’s more complicated. I lift every second day, and my own data shows exactly why.
Key takeaways
- Strain is scored on a 0–21 scale and gets harder to raise the higher you go.
- It’s mainly based on how long your heart rate is elevated, and by how much.
- My logged weightlifting sessions average a strain of just 8.7, with an average heart rate of 109 bpm.
- After my highest-strain days (17+), my next-morning recovery averages 55%, against 66% after easy days.
- Track lifting in a proper log and use strain as a rough daily load gauge.
How is WHOOP strain calculated?
Strain measures the load on your cardiovascular system across the day, from 0 to 21. It’s logarithmic: going from 10 to 11 is far easier than going from 18 to 19. A long walk adds a little. A hard spin class adds a lot.
- Light (0–9): a rest or easy day.
- Moderate (10–13): a normal training day.
- High (14–17): a hard session.
- All out (18–21): rare, very demanding days.
Why does lifting score low?
Because heart rate doesn’t tell the full story of strength work. A heavy set of five squats is hard on muscles and the nervous system, but it’s short, and you rest two or three minutes between sets. Your heart rate rises, then falls. The total can look modest.
My own numbers prove it. The weightlifting sessions WHOOP has logged for me average 37 minutes, a strain of 8.7 and an average heart rate of 109 bpm. On a heart-rate scale, that’s only a little above my walks, which average 5.9. Nobody who lifts properly thinks a heavy session is barely harder than a walk. The scale just can’t see the muscular work.
WHOOP has recognised this and added muscular load tracking for strength workouts. It’s a real improvement, but I still don’t judge a lifting session by its strain number.
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Where strain is useful: total daily load
Strain shines when you look at the whole day. Training plus 10,000+ steps plus a stressful day adds up, and my data shows it costs me the next morning:
- Previous day strain under 10: recovery averages 66%.
- 10 to 17: about 60%.
- 17 and above: 55%.
That’s why I match the next day’s training to recovery, not to the plan alone. See the recovery score explained.
How do I use strain as a lifter?
- The training log is the truth. I track sets, reps and weights in the RP Hypertrophy app. That’s how I know if I’m progressing.
- Strain shows total daily load, not how good a lifting session was.
- Match strain to recovery. Green day, higher strain is fine. Red day, keep it low.
- Watch the next morning. The real test of a big day is how your recovery looks after it.
- Log your workouts. Tagging a session as strength training helps WHOOP read it properly. I haven’t logged every session, and I should.
What about cardio?
This is where strain works best. For zone 2 work, strain helps you see consistent weekly volume. For intervals, it shows how deep you went. See zone 2 cardio and VO2 max and longevity.
Is there a perfect weekly strain?
No. The goal isn’t maximum strain. It’s the right strain for your recovery, consistently, for years. After 40, the men who progress are the ones who don’t keep breaking themselves. See why recovery takes twice as long at 50.
Muscle needs fuel too. I eat protein at every meal and take 10 PerfectAmino tablets a day, plus 10g creatine. And I check the result monthly on a Hume Body Pod, because muscle gained is the real scoreboard for a lifter.
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Join free →Frequently asked questions
What is a good daily strain?
It depends on your recovery. On a green day, moderate to high strain is fine. On a red day, keep it light.
Why did my heavy leg day score low strain?
Short sets and long rests keep average heart rate modest. The muscular demand is still real. My lifting sessions average a strain under 9.
Does WHOOP track reps and weights?
WHOOP has added strength tracking features, but I still use a dedicated training app for my log.
Can strain be too high?
Repeated high strain on low recovery is the recipe for burnout and injury, especially after 40.
Do walks count towards strain?
Yes. My walks average a strain of about 6.
Does LifeWave X39 affect strain?
No such claim is made. X39 is not intended to diagnose, treat, cure or prevent any disease.
Related reading
WHOOP Recovery Score Explained · Is WHOOP Worth It After 40? · Zone 2 Cardio · Why Recovery Takes Twice as Long at 50
Full disclosure. This article is general information, not medical advice. Personal figures are from my own WHOOP data export (30 November 2023 to 19 October 2026) and are one person’s observations, not a study. My WHOOP link is a member referral link and I receive free membership time when someone joins through it. Hume Health and PerfectAmino links are affiliate links. LifeWave products are not intended to diagnose, treat, cure or prevent any disease. As an authorised LifeWave Brand Partner I have a financial interest in promoting LifeWave products.
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