How the warm-up calculator works
Why ramping beats jumping in
Warm-ups serve three systems: tissues (temperature and elasticity), movement (grooving the pattern with increasing load), and nervous system (rate coding ramps up). A 4–5 step ladder at 40/60/80/90% accomplishes all three in ~8 minutes — while the classic "stretch and go" serves none of them and the 10-step marathon pre-exhausts the work sets.
The 90% ceiling
Warm-up loads above ~90% of the work set start consuming the same recovery the work set needs — particularly on heavy singles. The ladder ends at 90% with a single: close enough to the work load to feel real, far enough below to leave the tank full. This is also why "work up to it" without a plan so often overshoots.
Scaling the ladder
Light work sets (under 135 lb) need only 2–3 steps. Very heavy sets (400+) benefit from a 6th step at ~95% for singles. The general shape holds: doubling steps, single reps approaching the top, rest periods lengthening as loads approach work weight. The calculator sizes the steps; the principle sizes the count.