Deloads are used in powerlifting to dissipate built up fatigue. To push adaptation in advanced individuals, fatigue must be pushed beyond your current level of recovery….and this masks “fitness”. During a taper and/or deload we want fatigue to drop below recovery ability so we can “realize” our new abilities.
Example, block 1 we push fatigue up and fitness falls. There’s no way we could hit a PR deadlift 5 rep max. So block two we lower volume, start pulling higher weights, maybe focus on hitting a 5RM, s week later hitting a 3rm, and maybe a top double. Fitness is high, fatigue is low. Adaptation is minimal, but we can get good at moving heavy things.
We slowly add volume back in, to drive adaptation and fitness falls again, we are not setting PRs, we just punching the clock, accumulating work, so we can realize it again in 4-6 weeks
I’m bodybuilding it’s kinda the same, except some CAN walk the line of putting in enough work, recovering slightly about fatigue before the next session. But I believe this isn’t as effective as having structured time periods of slight overtraining and then recovery weeks