Your smartwatch records every heartbeat during every workout — but most fitness apps only show you calories burned or distance covered. TRIMP (Training Impulse) turns that heart rate data into a single number that reflects how hard your body actually worked, not just how far you went. Developed by sports scientist Dr. Eric Banister in the 1970s, TRIMP is the same metric used by professional sports teams worldwide.
Here’s how it works and why it matters for your training.
How Does TRIMP Work?
TRIMP combines two factors: workout duration and heart rate intensity. A 45-minute jog at a moderate heart rate produces a different TRIMP score than a 20-minute interval session that pushes your heart rate to 90% of its maximum — even if both burn similar calories.
The calculation uses your heart rate reserve (the difference between your resting and maximum heart rate) to personalise the result. An exponential weighting factor accounts for the fact that higher-intensity exercise creates disproportionately more physiological stress. Ten minutes at 90% of your maximum heart rate is far more demanding than ten minutes at 60%, and TRIMP reflects that gap mathematically.
Banister’s original research also applies gender-specific coefficients, recognising that male and female cardiovascular systems respond differently to the same relative intensity.
Why TRIMP Matters More Than Calories
Calories burned is an output metric — it tells you energy was expended. TRIMP is an internal load metric — it tells you how much physiological stress your body absorbed. That distinction matters because internal load is what drives adaptation.
Two runners might cover the same 5km distance. One finishes with an average heart rate of 145 bpm; the other with 170 bpm. Their calorie counts could be similar, but their TRIMP scores — and the training effect on their bodies — are vastly different. Research published in the British Journal of Sports Medicine confirms that internal load monitoring is critical for determining training outcomes and preventing injury.
Professional teams in the Premier League, NFL, and Olympic programmes use TRIMP to balance training load across a season. Now, with wearable heart rate monitors in nearly every smartwatch, that same data is available to anyone who works out with a watch on their wrist.
How Can You Track Your TRIMP Score?
If you own an Apple Watch, Garmin, Polar, or any device that writes heart rate data to Apple Health or Google Health Connect, you already collect the raw data TRIMP needs — see our device setup guides to make sure your data is flowing. What you need is an app that processes it.
ScoreVitals calculates a TRIMP-based session score automatically for every workout — running, cycling, swimming, strength training, and 25+ activity types. You finish your workout, the data syncs, and you receive a score that tells you exactly how hard your body worked. No manual logging required.
Over time, tracking your TRIMP across sessions reveals patterns: which workouts push you forward, which barely register, and when you’re stacking too much load without enough recovery.
Your watch already tracks every heartbeat. TRIMP is the science that makes those heartbeats meaningful. Download ScoreVitals and see your first session score after your next workout.