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Training Impulse (TRIMP)

Quantify a session's training load using duration and heart rate.

How it is calculated

The tool applies the Banister formula with the male weighting constants. First the heart-rate reserve fraction: HRr = (avg − rest) ÷ (max − rest). Then TRIMP = duration × HRr × 0.64 × e1.92 × HRr. Duration is in minutes and all heart rates are in beats per minute. The result is rounded to a whole number and the reserve used is shown as a percentage. Inputs that cannot be a real session give no result: duration must be above zero, every heart rate must be between 20 and 250, the average must be above the resting rate and no higher than the maximum. An average equal to or below resting therefore shows nothing rather than a score of 0. There is no female option; only one set of constants is used.

Worked example

A 45-minute run at an average of 150 bpm, with a resting rate of 60 and a maximum of 190. Reserve: (150 − 60) ÷ (190 − 60) = 90 ÷ 130 = 0.692, shown as 69.23%. Weighting: 0.64 × e1.92 × 0.692 ≈ 0.64 × 3.78 ≈ 2.42. TRIMP: 45 × 0.692 × 2.42 ≈ 75.3, displayed as 75. The same 45 minutes at a lower average of 120 bpm gives 32, far below 75, because the weighting grows exponentially with effort.

Try this example →

Common mistakes

  • Entering an estimated maximum such as 220 minus age without noting it. TRIMP depends on the reserve fraction, so a maximum that is too high lowers the score for every session.
  • Using a resting heart rate taken at a stressful moment instead of a calm morning value, which shrinks the reserve range.
  • Entering the average heart rate for the whole session including warm-up and rest, when the number intended is the average while working.
  • Typing hours into the minutes field. A 1.5 hour ride is 90 minutes, not 1.5.
  • Comparing a score from this tool with a watch's TRIMP, which may use the female constants or a different formula, and concluding one of them is wrong.

Sources

About this calculator

TRIMP (Training Impulse), developed by Eric Banister, quantifies how hard a workout was by combining session duration with heart-rate intensity into one number: TRIMP = duration (minutes) × heart-rate reserve fraction × a weighting factor (0.64 × e^(1.92 × HRr), the factor Banister published for men) that exponentially weights harder efforts more heavily than easy ones, since a hard interval session stresses the body disproportionately more than the same duration at an easy pace.

Endurance coaches and sports scientists use TRIMP to track cumulative training load across a week or season, feeding it into fitness-fatigue models (like the Banister impulse-response model) that help predict overtraining risk or plan a taper before a race. It gives a single comparable score across very different workouts — a short, intense interval session and a long, easy run can produce a similar TRIMP even though they look nothing alike on paper.

Enter your session duration in minutes plus your average, resting and maximum heart rate, and this calculator returns the Banister TRIMP score for that workout and the heart-rate reserve you averaged. It always uses the men’s weighting factor and has no sex setting, so scores for women are only approximate (Banister’s women’s factor is 0.86 × e^(1.67 × HRr).)

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