Session load (TRIMP)
Updated October 3, 2026 · Source: Banister, 1991
01What it is
A number that sums up the internal effort of a session: the longer you stay at a high heart rate, the bigger it is.
02How it’s calculated
TRIMP = minutes × HRR × a × eb × HRR HRR (fraction of heart rate reserve) = (average HR − resting HR) ÷ (max HR − resting HR).
Men: a = 0.64 and b = 1.92. Women: a = 0.86 and b = 1.67.
Runalis integrates the formula over the heart rate samples of the session. Without samples, it falls back on average HR, then perceived effort, then the percentage of vVO2max. The calculation below assumes a constant average HR.
03How to read it
60 minutes of easy running score about 85; a threshold session of the same length scores much more. The number rises faster than intensity does, which reflects the real cost of harder effort.
04What it’s used for
Each day’s load feeds fitness (CTL), fatigue (ATL), freshness (TSB) and the load ratio (ACWR).
05Limits
TRIMP depends on your max HR and resting HR: if they are wrong, the load is too.
Runalis is not medical advice. If you feel pain, stop and see a health professional.
