JBST CoreTemp Test (v.2.1.2026) – Web Form + Calculator

Athelete Data

Test date

Helper present? (recommended)

FTP (W)

PPO (W)

Use for warm-up wattage calculations

Step 1 start time

Safety note: there are potential risks of overheating — stay safe, ideally with a helper to watch you. No fan is used during the test; install the CORE iOS/Android app for core temp tracking; keep warm-up consistent.

Autosaves in this browser Stop-point = 20% below PO1

Before/After Measurements

Nude weight at start (kg)

Nude weight at end (kg)

Air temp (°C) / moisture (%) at start

Air temp (°C) / moisture (%) at end

Core temp before test (CT0)

Total fluids consumed during test (ml)

Clothing worn

Derived (optional)

Body mass change

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Estimated sweat loss*

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Note

*Sweat loss estimate assumes 1 kg ≈ 1 L, and that “fluids consumed” contributes to total loss: sweat loss (L) ≈ (start kg − end kg) + (fluids ml / 1000).

Step 1 – Warming up to 38°C

Block	Duration	% FTP	% PPO	Target watts (from selected basis)	Target watts (FTP)	Target watts (PPO)

If after 20 minutes core temp is still < 38°C, increase power to 85% FTP (or 64% PPO), but no higher.

Step 2 – CHECKPOINT 1: When 38°C reached (CT1)

Heart Rate 1 (HR1) bpm

Power Output 1 (PO1) watts

Core Temp 1 (CT1) at 38°C (record exact)

Time at CT1

Stop-point (20% below PO1)

Maintain HR1, gradually lower power, stop when reaching this power levevl --->

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The sheet’s rule: stop riding the moment you drop 20% below PO1 (i.e., 80% of PO1).

PO1	Stop at (80%)	PO1	Stop at (80%)
120	96	220	176
140	112	240	192
160	128	260	208
180	144	280	224
200	160	300	240

Step 3 – CHECKPOINT 2: when power drops 20% below PO1

Stop pedalling, do not use a fan yet or (ideally) drink any fluids (unless unwell). Immediately note:

Heart Rate 2 (HR2) bpm

Core Body Temp 2 (CT2)

Time at checkpoint 2

Optional: “end time” (for your own tracking)

Peak after stopping (CT3)

Core Body Temp 3 (CT3) peak

Heart Rate 3 (HR3) bpm

Time of peak (CT3)

Notes

Sheet note: questions and improvements please CLICK HERE
Use of this tool implies agreement with terms at www.JBST.com. (c) J.M.Beer MMXXVI.