What an Apple Health strength app should solve
HRV, resting heart rate, sleep, and activity trends can help explain why a session feels different than expected. The app still needs to translate those signals into a reasonable strength-training adjustment.
A useful strength app should reduce decision fatigue without pretending your body is the same every day. The best pages in this cluster focus on the moment before training: what should change, what should stay, and how to keep progress moving without making every workout a maximal test.