"I did 5 hours this week" says very little. Five hours of easy walking and five hours of intervals are completely different weeks. A training load number fixes that by weighting time by intensity. Then it becomes possible to compare weeks, see jumps, and plan.
Step 1: Heart-Rate Zones
Metrya reads the heart-rate curve of each workout from Apple Health and splits the time into five zones. Zones are based on your estimated maximum heart rate, using the Tanaka formula (208 − 0.7 × age). It behaves better than "220 minus age" at both ends of the age range. If your birth date isn't set, Metrya uses a default and marks the zones as estimated.
| Zone | Share of max HR | Load per minute |
|---|---|---|
| 1 · Recovery | below 60% | 1.0 |
| 2 · Aerobic | 60–70% | 1.6 |
| 3 · Tempo | 70–80% | 2.4 |
| 4 · Threshold | 80–90% | 3.6 |
| 5 · VO₂max | above 90% | 5.0 |
Gaps in the heart-rate data are not filled in. If the watch lost contact for 20 minutes, those 20 minutes don't become 20 minutes of Zone 1.
Step 2: Load = Zone-Weighted Minutes
A session's load is its minutes in each zone multiplied by that zone's weight, added up. This is close in spirit to TRIMP, a training-impulse measure used in sport science: time near your threshold costs much more than easy time.
Workouts without a heart-rate curve (a manual entry, a phone-only workout) get an estimate from duration and the intensity you choose. They are always marked as estimated.
Step 3: The Load Ramp (This Week vs Your Normal)
A single number for this week only means something next to your usual week. Metrya compares two values:
- Acute load: your total load over the last 7 days.
- Chronic load: your average weekly load over the last 28 days. This is what your body is used to.
The ratio between them is your load ramp. 1.0 means this week looks like your recent normal.
| Ratio | Band | Reading |
|---|---|---|
| below 0.8 | Detraining | Much less than usual. Fine for a rest week or a taper. |
| 0.8–1.3 | Steady | Close to what you are used to. |
| 1.3–1.5 | Building | A real step up. Fine for a planned block. Watch recovery. |
| 1.5 and above | Spike | A big jump over your normal. |
Step 4: Is Your Easy Work Easy?
A common finding in endurance training is that many people train in the middle too often: easy days too hard, hard days not hard enough. The zone mix shows your last 28 days as three parts:
- Easy: Zones 1–2
- Moderate: Zone 3
- Hard: Zones 4–5
Only sessions with a real heart-rate curve count, so estimated sessions don't make your mix look easier than it is. Many endurance plans aim for most of the time to be easy. If your Zone 3 share is large, your "easy" runs may be too fast.
Step 5: What Should I Train Today?
Load tells you what you have done. Recovery tells you how your body handled it. Metrya combines them into one line under the Recovery score:
Then the context adjusts it. If you trained much more than usual this week, the suggestion stays easy. If your load went up fast, it stays moderate. A Reserve under 30 makes it one step lighter. If you logged "Feeling unwell", it becomes a rest day.
The suggestion also gives a time range, like "about 30–45 min at a steady effort". That range comes from your own workouts over the last four weeks. Until you have four weeks of workouts, it uses a typical day and says so. A bar fills as today's workouts sync.
Every Session Gets a Read
Open any workout from Apple Health and you get a scrubbable heart-rate curve, time in each zone, pace splits when there is distance, the session's load, and what it cost overnight: the next night's HRV and resting heart rate compared with your 30-day baseline. You can add how hard it felt (RPE), a note and tags.
When a new workout arrives, Metrya shows a short summary the next time you open the app: a ring with the load it added compared with a typical session for you, and what it did to your week.
Where the Workouts Come From
Metrya doesn't record workouts. It reads them from Apple Health, so it works with the Apple Workout app, Garmin, Strava and anything else that syncs to Health. Duplicate samples from the same app are counted once, and impossible distances are dropped rather than shown.
Limits
- Heart rate isn't everything. Strength training raises fatigue more than heart rate suggests. Its load is usually underestimated.
- Zones are estimates. A formula for max heart rate can be off by 10 beats or more for some people.
- History is limited. Workouts are imported for the last 30 days, so the 28-day chronic load is always based on recent weeks.
- A suggestion, not a coach. If you follow a plan or a coach, use this as extra information.
See your load against your own normal.
Metrya reads the workouts already in Apple Health (from Apple Watch, Garmin, Strava and others) and turns them into zones, load and a daily suggestion. On your iPhone, free.
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