Yes: the Watch app runs a whole workout from your wrist, and Apple Health is where Rhythm reads your heart rate, sleep and recovery signals.
On the Watch you can log a set, change the weight or the reps with the crown, start, extend or skip your rest, and add an exercise from a catalogue that lives on the watch itself. It keeps working with your phone in a locker on the other side of the gym, and the sets reconcile when the two reconnect.
With your permission, Apple Health sends heart rate, resting heart rate, heart-rate variability (the beat-to-beat change in your heart rhythm), active energy, sleep, breathing rate, and — on Apple Watch models with the sensor — your wrist temperature during sleep. It also reads menstrual flow and menopausal state, if you or another app record them there, and never writes cycle data back. Live heart rate and calories from a Watch workout flow into the workout summary, and Rhythm writes your finished workouts and active energy back to Health.
Confidence, not load. Clear and consistent signals mean today's suggestion is offered with more of it; thin signals, or two devices that disagree, mean Rhythm says so instead of guessing. Your working weights come from the sets you have actually logged.
A raw number left on its own. Rhythm turns what Health sends into plain words and says what it means for today, and every reading in the app opens to a “why” in one tap.
Wrist temperature never sets your cycle phase. At most it changes how a cycle estimate is worded, and only with hedged, medium confidence. Your cycle dates and phase are worked out on your phone and are never sent to our servers, whatever you connect. And a wearable is optional: Rhythm reads your training log first.