TRIMP Calculator (Banister Training Impulse)
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/9/2026
TRIMP is calculated with duration × heart rate reserve fraction × an exponential weighting factor (different for men and women). For a man training 60 minutes with an average HR of 150 bpm (resting HR 60, max HR 190), the TRIMP is about 100.4.
Explanation
TRIMP (TRaining IMPulse), developed by Eric Banister from the 1970s to the 1990s, quantifies the load of a cardio session into a single number, combining two pieces of information: the duration of the effort and its relative intensity, measured by the fraction of heart rate reserve used (the gap between the session's average HR and resting HR, relative to the full gap between max HR and resting HR). Unlike a simple duration × intensity multiplication, TRIMP weights this intensity EXPONENTIALLY rather than linearly: a high-intensity effort weighs disproportionately more in the score than an effort twice as long but half as intense, reflecting the fact that the physiological stress response (notably lactate production) itself accelerates exponentially as intensity rises. The weighting factor differs slightly between men and women (1.92 versus 1.67 as the exponent) because this lactate-response curve as a function of intensity was measured as statistically different between the sexes. This calculation assumes a max HR already known or estimated — see our max heart rate formula comparison calculator if you haven't measured it directly. TRIMP complements tools like our acute:chronic workload ratio calculator (ACWR), which tracks how load evolves over several weeks: the daily or per-session TRIMP is exactly one of the raw indicators that can feed into that weekly tracking.
Example: a 60-minute session, average HR 150 bpm
Inputs
Duration: 60 min. Resting HR: 60 bpm. Max HR: 190 bpm. Average HR: 150 bpm.
Calculation
HR reserve fraction = (150 − 60) ÷ (190 − 60) ≈ 0.6923. TRIMP = 60 × 0.6923 × 0.64 × e^(1.92×0.6923) ≈ 100.4.
Result
This session represents a TRIMP of about 100.4.
Frequently asked questions
Why is the weighting factor exponential rather than linear?
Because the physiological response to effort (particularly blood lactate accumulation) doesn't rise linearly with intensity: it accelerates markedly beyond a certain threshold, generally associated with the lactate threshold. An exponential weighting therefore better reflects the real physiological cost of a high-intensity effort than simple proportionality, which would strongly underestimate the most intense sessions.
Why does the factor differ between men and women?
Because the studies that established this formula measured a statistically different lactate-response curve to intensity between the sexes, with an exponent of 1.92 for men versus 1.67 for women. These values remain population averages, not an exact individual measurement of each person's lactate response.
What is a TRIMP score used for day to day?
It allows objectively comparing the load of two very different sessions (a long easy ride versus a short, intense session, for example), and tracking how total training load evolves over a week or a month — tracking that directly feeds load-management tools like the acute:chronic workload ratio, useful for spotting too rapid an increase in training volume, a documented injury risk factor.