Strength Coaching
METTLE
A strength coach that shows the reason behind every number.
Mettle is a strength coach that shows its work. Goals, experience, equipment, schedule, and training history shape an adaptive program on iPhone. Deterministic logic owns sets, reps, rest, load progression, and deloads. Apple’s on-device model can select and explain exercises only from curated candidates. Logged reps and loads drive the next prescription, while RPE can shape coaching depth. Mettle remains in active development, and final private iCloud behavior is not yet verified.
Why it exists
A strength coach that shows the reason behind every number.
Mettle gives deterministic training logic control of every prescription. On-device intelligence selects from curated candidates and explains the plan at the lifter’s level, so adaptation never becomes a black box.
No hidden data path
Useful from the first input to the final result.
- 01
Define the Training Context
Choose the goal, experience, equipment, training days, session length, units, and optional bodyweight.
- 02
Generate a Structured Program
On-device AI selects from curated exercise candidates while deterministic composition still produces a complete plan if the model is unavailable.
- 03
Run the Session
See the last performance and exact “Why this?” rationale, log sets, use the planned rest timer, and optionally control the phone session from Apple Watch.
- 04
Adapt the Next Prescription
Logged sets drive the next progression, the program calendar schedules deloads, and completed training, RPE history, and note language can inform competence and coaching depth.
What it does
Purpose-built for one private workflow.
Every Number Has a Reason
Double progression and scheduled deload logic produce the sets, reps, loads, and evidence behind “Why this?”, not an unconstrained language model.
Coaching that Changes Altitude
The same deterministic program can be explained gently to a new lifter or with more training detail to someone experienced, without hiding control.
Workout Continuity
Live Activity, a resumable session, optional HealthKit, a Watch remote, custom exercises, and CSV export keep the training record useful.
Privacy is architecture
A shorter data path.
A clearer privacy boundary.
Core programming and coaching run on-device and retain a deterministic fallback. The source prefers private iCloud when that capability is configured and falls back on-device; the reviewed entitlement currently lacks iCloud, so final sync behavior remains unverified. HealthKit is optional, and the Watch experience controls an active phone workout rather than acting as a standalone trainer.
Read the full privacy modelBefore release or install
Questions worth asking.
The design prevents the language model from owning those decisions. Apple’s on-device model can select and explain exercises only from curated candidates; a deterministic engine owns sets, reps, loads, rest, double progression, and deload logic. The evidence behind a prescription is what Mettle shows in “Why this?”.