Trimp Training Impulse
Calculator

TRIMP (Training Impulse) combines both the duration and intensity of a session into a single score, so a short, hard interval workout and a long, easy run can register meaningfully different training loads even if their durations are similar. Duration alone ignores how hard the effort actually was.

The classic Banister formula multiplies session duration by average heart rate reserve fraction and an exponential weighting factor that increases with intensity, so higher-intensity minutes count for disproportionately more training stress than easier minutes.

Physiological stress, particularly the shift toward glycolytic metabolism and lactate accumulation, increases disproportionately as effort climbs toward and past threshold, so a linear weighting would understate how much harder efforts truly tax the body compared to easy ones.

Summing daily TRIMP scores gives a weekly training load figure you can track over time, watch for sudden spikes, or feed into an acute:chronic workload ratio to monitor whether your training stress is progressing safely or ramping too quickly.

The original formula does rely on heart rate data, since it uses heart rate reserve as its intensity measure, though some modern variants substitute power output or pace-based intensity zones for sports or situations where heart rate data isn't reliable or available.