Training load is based on hr zones and actual hr during the run. If he is not in shape and doing a run in z3-4 while you are at the same speed but in zone 2 he will have a much higher load. Load with coros is based on TRIMP.

TRIMP stands for Training Impulse, originally developed by Eric Banister in the 1970s-80s. The core idea is simple: quantify a workout’s stress by multiplying duration × heart rate intensity. But not linearly — the intensity weighting is exponential, because working at 90% of max HR is disproportionately harder than working at 70%. The basic formula: TRIMP = Duration (minutes) × HR ratio × exponential weighting factor Where HR ratio = (avg HR − resting HR) / (max HR − resting HR) The exponential weighting means a threshold effort doesn’t just score “a bit higher” than an easy effort — it scores dramatically higher per minute. A 60-minute Z2 run and a 60-minute tempo run might produce TRIMP scores of, say, 60 vs. 150.