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Thursday, March 26, 2026

How WHOOP Calculates “Strain”. How important Strain data for Tennis

 Question: I am a tennis player. I am wearing the band near my wrist. I have done my normal routine workouts and a tennis session. The whoop band shows my strain percentage has reached its maximum. I feel all ok because this is my normal routine and I in fact usually do one more similar session everyday. What is going wrong?

This is a very good and important question, especially for a tennis player. The short answer: Nothing may be “wrong” with you — but the WHOOP Strap may not be interpreting tennis correctly.

Let’s break this properly.


1. How WHOOP Calculates “Strain”

WHOOP strain is mainly based on:

  • Heart rate

  • Time spent in heart rate zones

  • Heart rate variability (HRV)

  • Recovery score

  • Sleep

  • Respiratory rate

It does NOT understand tennis workload directly (like number of serves, sprints, direction changes, mental stress, etc.). It only sees heart stress, not sport stress.

This is very important.


2. Why It Shows Max Strain Even If You Feel Normal

This is very common in sports like tennis, badminton, squash, football.

Possible reasons:

Reason 1 — Wrist Position Problem

You said you are wearing it near the wrist. For tennis players this is a big issue.

During tennis:

  • Wrist movement is very high

  • Racquet vibrations

  • Grip pressure

  • Sweat

  • Impact shock

All these disturb heart rate readings → WHOOP thinks your heart rate is higher than reality → Strain becomes very high.

WHOOP themselves recommend upper arm or bicep band for racquet sports.

This alone might fix your problem.


Reason 2 — WHOOP Thinks Your Normal Training Is “Too Much”

WHOOP learns your body slowly. If:

  • You are already very fit

  • You train twice a day normally

  • WHOOP is new

  • Sleep data not stabilized yet

Then WHOOP may think your normal training is overtraining.

WHOOP needs 2–3 weeks minimum to learn your baseline.


Reason 3 — Tennis Is Interval Sport

Tennis is:

  • Sprint

  • Stop

  • Jump

  • Serve

  • Rally

  • Rest

  • Sprint again

This causes heart rate spikes repeatedly, which WHOOP interprets as very high cardiovascular strain — even though muscle fatigue and real fatigue may be normal for you.

So for tennis players:

WHOOP strain is often high even when training load is normal.


4. Important: Fitness Coach vs Device

In sports science, devices are tools, not decision makers.

Training decisions should consider:

  1. Sleep

  2. Muscle soreness

  3. Mood

  4. Motivation

  5. Reaction speed

  6. Resting heart rate

  7. HRV

  8. Match performance

  9. Injury risk

  10. Coach observation

One number called “Strain” should not cancel a training day.


5. What Many Professional Athletes Do

Many tennis players and athletes using WHOOP Strap:

  • Wear bicep band, not wrist

  • Ignore strain for skill sessions

  • Use WHOOP mainly for:

    • Sleep

    • Recovery

    • HRV trends

    • Resting HR

    • Overtraining trends over weeks (not single day)

WHOOP is better for recovery tracking than for tennis workload tracking.


6. What I Suggest You Do

Very important practical steps:

Change this immediately:

  1. Wear WHOOP on bicep / upper arm

  2. Use Strain only as trend, not daily decision

  3. Follow this rule:

Recovery

Training

Green

Full training

Yellow

Normal but monitor

Red

Light training / technique

Red + Poor sleep + Muscle pain

Rest

Not based on strain alone.


7. Simple Reality About Tennis Training

If:

  • This is your normal routine

  • You feel fresh

  • Performance is good

  • No injuries

  • Sleep is good

  • HRV not dropping continuously

Then your body is adapted, but WHOOP is still learning or misreading.

Device should learn your body.
You should not change your training immediately because of device.


8. One Very Important Concept

Remember this line:

Fitness trackers are good at measuring fatigue.
Athletes are good at feeling fatigue.
Coaches are good at managing fatigue.
The best decisions use all three.


9. If You Want To Use WHOOP Properly For Tennis

Track these instead of strain:

  • Sleep performance %

  • HRV trend (7 day)

  • Resting heart rate trend

  • Recovery %

  • Respiratory rate

  • Feeling score (1–10)

  • Muscle soreness (1–10)

  • Motivation (1–10)

This is much more useful for tennis players.



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