Reminds me of how "confusing the muscle" came and went out of style as people realized you need specificity of training and you need to train a muscle with the same motion during its supercompensation recovery phase for it to further grow.
As a gross oversimplification: when you train a muscle hard, it accumulates low-level damage. This is why if you train continuously without any recovery, your ability level goes down, not up. The recovery phase is when your body repairs all that accumulated damage and builds the muscle back. Only, it doesn't stop at the level you started at, it goes past that and makes it a little stronger than it was. This is the supercompensation phase. If you just let it be, performance will eventually return to where you started at. But if you train again during this phase, you can reset the cycle, starting from a higher point.
