Why below your true max
Basing percentages on 90 percent of your real max builds in a buffer. That buffer means your top sets are achievable, you accumulate quality reps, and you avoid grinding maximal singles every week.
A training max is a working number below your true one rep max, usually about 90 percent, used to set your program's weights.
A training max, or TM, is a deliberately conservative estimate of your max, typically set at about 90 percent of your true or estimated one rep max. Programs like 5/3/1 calculate every working set as a percentage of the TM rather than your actual max. Using a submaximal number keeps your prescribed weights manageable so you can hit all your reps and progress steadily.
Basing percentages on 90 percent of your real max builds in a buffer. That buffer means your top sets are achievable, you accumulate quality reps, and you avoid grinding maximal singles every week.
In percentage based plans, every set is TM times a percentage. A 100kg TM gives a 65kg, 75kg, and 85kg progression, so the TM is the single anchor for your whole cycle.
You bump the TM by a small fixed amount each cycle, often 2.5kg upper body and 5kg lower body, rather than testing a true max constantly. Slow TM growth keeps the buffer intact.
A training max is a working number below your true one rep max, usually about 90 percent, used to set your program's weights.