TRIMP Training Load Calculator

Estimate the TRIMP training load of any session from duration and average heart rate. The same load model The Training Notes uses.

What this calculator does

TRIMP (TRaining IMPulse) estimates the cardiovascular cost of a session from duration and average heart rate. It's the same model The Training Notes uses to compute your weekly Effort Units and adjust the next week's plan.

TRIMP solves a problem that simple metrics don't: a 30-min hard interval session and a 60-min easy ride can produce the same fatigue, but very different adaptations. TRIMP weights HR exponentially, so time spent at high HR contributes disproportionately more load. That's why it correlates better with perceived exertion and recovery demand than minutes or distance alone.

How to use it

Get average HR from a chest strap or wrist optical reading (chest is more accurate for intervals).
Enter session duration in minutes.
Use your real resting and max HR — the defaults are placeholders.
Use the band (recovery / moderate / hard / very hard) as a sanity check on what you actually felt.

Formulas

Banister TRIMP

TRIMP = duration × HRR × 0.64 × e^(b × HRR), where HRR is the heart rate reserve fraction and b = 1.92 (male) or 1.67 (female). The exponential weighting is what makes hard intervals 'cost' so much more than easy steady-state.

Limitations and caveats

TRIMP is HR-driven, so it under-counts true strength sessions where HR stays low.
It under-counts very short, very high efforts (sprints) — those sit outside HR's response window.
Use it for trends across weeks, not single sessions. Day-to-day TRIMP is noisy.

Worked examples

Example 1

A male runner with a resting heart rate of 50 bpm and a max heart rate of 190 bpm completes a 45-minute run at an average heart rate of 145 bpm.

Calculation. First, calculate the heart rate ratio: (145 - 50) / (190 - 50) = 0.678. Then, multiply by the duration and the male gender-specific factor: 45 min * 0.678 * 1.92 = 58.6 TRIMP.

Takeaway. This TRIMP score can be logged and compared to other workouts to manage training load over time.

Example 2

A female lifter with a resting heart rate of 60 bpm and a max heart rate of 185 bpm finishes a 75-minute strength session with an average heart rate of 115 bpm.

Calculation. Calculate the heart rate ratio: (115 - 60) / (185 - 60) = 0.44. Then, multiply by the duration and the female gender-specific factor: 75 min * 0.44 * 1.67 = 55.1 TRIMP.

Takeaway. Track TRIMP session to session to ensure you are progressively overloading your work capacity.

Common mistake: Using a generic '220 - age' formula for max heart rate can lead to inaccurate TRIMP scores.

Fix. For a more precise HR_max input, perform a field test or use the highest heart rate observed during a maximal effort in the last several months. A more accurate HR_max produces a more reliable training load.

Source: Banister, E.W. (1991). Modeling Elite Athletic Performance.

Frequently asked questions

What's a 'normal' weekly TRIMP?

Recreational athletes typically run 200–500 weekly TRIMP. Endurance-focused athletes can go 800+, but only with a structured base.

How does this differ from Strava's Suffer Score / Garmin Training Load?

Both are TRIMP-derived models with proprietary weightings. The numbers don't compare directly — but the trend (rising vs falling week-over-week) tells the same story.

Should I use this for strength sessions?

Not really. TRIMP is for cardiovascular load. The Training Notes uses a separate volume-load calculation for strength and combines them into Effort Units.

What if my watch doesn't give me average HR?

Most watches do — check the post-session summary. If not, a chest strap with a free app like Strava or Wahoo Fitness will.