EN
Recovery and breathing
Your muscle recovery, muscle by muscle
48, 60 or 72 hours depending on the muscle, fatigue that fades linearly, and a pace slowed down by a short night, a high resting heart rate or age: the exact model behind the recovery percentage shown.
3 min read Updated October 9, 2026
The principle
After a session, a muscle needs time to repair and perform well again. That time depends on its size, on how much work it received and on your ability to recover that day. Azetta sums it up as a recovery percentage per muscle, from 0% (exhausted) to 100% (fresh), with the number of hours left before full recovery.
The Azetta method
The recovery window
| Muscles | Window |
|---|---|
| Quads, hamstrings, glutes, lower back | 72 h |
| Chest, lats, mid back, shoulders, traps | 60 h |
| All the others (arms, calves, abs…) | 48 h |
Fatigue
Each working set (warm-up excluded) adds one unit of load to its primary muscles and half a unit to its secondary muscles. Each load fades linearly over the muscle's window; 10 sets make up a full load.
Load, reps and perceived effort don't change this calculation: only the number of sets counts.
What slows recovery down
- Sleep from the last night (from Health or your watch): under 6 h → window +10%; under 5 h → +20%.
- Resting heart rate: at least 5 beats above your baseline → +10%; at least 8 above → +15%. The baseline is the average of your minimum resting heart rates from the 33rd to the 3rd day before, and requires at least 7 days of measurements.
- Age, for a heavily loaded muscle (6 sets or more): +10% from 50, +20% from 60.
The total slowdown stays between ×1.0 and ×1.5.
Where it is used
- The Progress page shows recovery based on the sets from the last 6 days.
- The week's forecast adds the planned sessions.
- In a custom session, the "Recovered ones" button picks up to 4 muscles that are at least 90% recovered.
Why this choice
- Muscle protein synthesis stays elevated for about 24 to 36 hours after a heavy session, and the guidelines leave at least 48 hours between two sessions for the same muscles: the 48 to 72-hour windows follow this order of magnitude, longer for the big leg and back muscles.
- A resting heart rate higher than usual is one of the simple signs of fatigue or stress tracked in athlete monitoring.
- Counting sets, without guessing intensity, keeps the model simple and predictable.
Limits
- This model is an estimate, not a measurement: soreness, stress or illness are not seen.
- Recovery is there for information: the weekly program, for its part, spaces sessions with its own rule of 48 hours between two sessions for the same muscle groups.
- Without a watch or Health data, sleep and heart rate are not taken into account.
References
- MacDougall JD, Gibala MJ, Tarnopolsky MA, MacDonald JR, Interisano SA, Yarasheski KE. The time course for elevated muscle protein synthesis following heavy resistance exercise. Canadian Journal of Applied Physiology, 1995;20(4):480-486.
- Buchheit M. Monitoring training status with HR measures: do all roads lead to Rome? Frontiers in Physiology, 2014;5:73.
- American College of Sports Medicine. American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Medicine & Science in Sports & Exercise, 2009;41(3):687-708.