The WHOOP Strain Score, explained
Strain is the cardiovascular load your body carried today — measured on a 0-21 logarithmic scale, calculated continuously from heart-rate time spent in each zone.
See your strain on the dashboardWHOOP Strain quantifies how much physical and cardiovascular load you've placed on your body in a 24-hour day. Unlike active calories or step counts, it weights time in higher heart-rate zones disproportionately — so a 20-minute intense interval session can push your score higher than a 2-hour walk. The scale is logarithmic, which is why moving from 14 to 18 takes far more effort than moving from 6 to 10.
Strain runs on a 0-21 logarithmic scale based on Borg's Rating of Perceived Exertion. Zero means you stayed completely sedentary. Around 21 represents the most extreme physical day a human can sustain. WHOOP tracks two strain values: Day Strain (sum of all cardiovascular load between waking and sleeping) and Activity Strain (load during a single tracked workout).
WHOOP samples your heart rate every second from the optical sensor, then weights time spent in each heart-rate zone using your personal maximum heart rate. Time at 80-90% of HR-max contributes far more than time at 50-60%. The score also factors in your recovery from the morning: if you started the day at 90% recovery, the same workout will score lower strain than if you started at 20%. This is why two identical runs on different days can produce different strain numbers — your physiology responded differently.
WHOOP groups daily strain into four bands. The score is logarithmic, so the bands are not evenly sized.
Light
A typical low-activity day. Walking, light errands, short stretching. Builds aerobic base over weeks but no cardiovascular stress.
Moderate
A solid training day — a recreational run, a gym session, an active commute. Most consistent athletes spend 4-5 days/week here.
High
Hard interval work, a long ride, a competitive match. Productive when matched by a green recovery; risky when stacked on yellow or red.
All Out
Race day, ultra-endurance event, two-a-day training. Days at this level should be deliberate and followed by extra recovery time.
More strain is not better. WHOOP gives you a recommended strain target each morning, weighted by your recovery score. Match your day to the recommendation.
- 01
Match strain to recovery
On a green recovery (67%+), push toward your high-end target. On a red recovery (<34%), keep strain in the light-to-moderate zone — pushing through a red day delays adaptation.
- 02
Progress your weekly load gradually
Increase your weekly total strain by no more than 10-15% week-over-week. Sudden 30%+ jumps are correlated with overuse injury risk and recovery decline.
- 03
Mix intensities through the week
A common 7-day pattern: 1-2 high-strain days, 3-4 moderate days, 1-2 light/recovery days. This polarized model produces better adaptation than chronically moderate training.
- 04
Watch for trend mismatches
If your strain trend is rising but HRV is dropping over 7 days, you're accumulating fatigue faster than you're recovering. Pull back proactively.
What is a good daily WHOOP Strain score?
There isn't a universal 'good' number. WHOOP recommends a target each morning based on your recovery — typically 10-14 for active recovery days, 14-18 for training days. Chasing a fixed daily number ignores how recovered you actually are.
Why is WHOOP Strain logarithmic instead of linear?
Cardiovascular stress scales non-linearly with intensity. Doubling your heart rate effort more than doubles the physiological cost. A logarithmic scale gives appropriate weight to truly hard efforts and prevents long, easy days from inflating the score.
How is Day Strain different from Activity Strain?
Activity Strain is the load from a single tracked workout. Day Strain is the cumulative cardiovascular load across all of your waking hours, including workouts plus everything else — commuting, stairs, stress responses, sex, hot meals. Day Strain is always equal to or higher than your highest activity of the day.
Can high strain hurt my recovery?
Yes. Repeatedly stacking high-strain days without matching recovery time produces sustained drops in HRV, elevated resting heart rate, and slower next-day recovery scores. WHOOP's strain target is the primary lever to avoid this.
Why did my strain change after a recovery jump?
The same workload produces different strain when your starting recovery shifts. A run that scored 13 on red recovery may score 11 on green recovery — your cardiovascular system handled the load with less stress on the higher-recovery day.