Fitness trends

1

What do Fitness trends show?

Whether a few slow readings rose, fell or held. A card gets a word only when the change passes its everyday wobble.

On Fitness, Trends gives each slow reading a card. A card says Rising, Falling or Steady, and Effort says Quicker or Slower. Cards that changed come first, and a line under the heading counts them against the ones that held.

Five cards can appear: Endurance fitness, Resting heart rate, Cardio fitness, Heart rate recovery and Effort. Four of them read your watch and your runs. Endurance fitness reads your training. Heart rate variability and walking pace are left out on purpose.

A word names a direction, not a verdict. A falling resting heart rate is usually the fitter direction, because regular exercise lowers it. A falling VO2 max is not. Both cards read Falling and both turn amber, since amber marks a change in either direction.¹

2

What goes into it?

Your watch's cardio fitness estimate, runs on a route you repeat, resting heart rate, recovery after a workout and your training base.

Cardio fitness is the VO2 max estimate Aera reads from Apple Health, the last value of each day. A reading is a day the estimate changed, so a value carried over from earlier days is not counted again.

Effort comes from runs only, never walks or rides. A route you repeat is a stretch you have run in at least 3 different workouts. Each run over it is a pass. A pass counts when it has an average heart rate and lasts at least 3 minutes.

Aera follows the route with the most passes that have a heart rate. It also drops a pass whose pace is outside 0.7 to 1.4 times the pace of its own run, such as one timed over a route drawn for another distance. It then shows your pace at that route's usual heart rate. This is not Heart drift, which compares two halves of one run.

Resting heart rate is the resting rate Apple Health records. Heart rate recovery is the one-minute figure Aera reads from Apple Health: how far your heart rate falls in the first minute after a workout. Each day's last value is used. See the first minute.

Endurance fitness is not a reading from your body. It follows your training base, the number Training load calls your base on Home and your usual on a workout's page. Cardio load shows how that number is built.

Beside the trends, Training focus shows the easy share of your heart rate zone time over the last 4 weeks. It has no word.

3

How is each reading worked out?

Each card sets a recent value against where it started, behind a cut-off. Aera chose every cut-off, and none is taken from a study.

The comparison covers the last 12 weeks, ending today. Each reading is set against where it stood at the start of that window, never against a usual that rises as you do.

Cardio fitness needs 6 readings in the window, spread over at least 28 days. The start is the value carried into the window, or the first reading in it, and the latest is the last reading. A change of 1.5 points or more counts.

Effort looks at passes inside the 12 weeks and divides each pass's speed by its average heart rate. It compares the middle value of the first three passes with the middle value of the last three. If the feels-like temperature of those two sets differs by more than 6 °C, the card reads Steady, however big the change. If either set has no temperature, the passes count as comparable.

Effort needs 5 passes in all. A change of 5% or more in speed per heartbeat counts.

Resting heart rate sets the average of the last 28 days against the average of the same length of time before the window. Each needs 21 nights. A move of 2 beats a minute or more counts, and lower is fitter.

Heart rate recovery uses the middle value of the last 28 days against the middle value of the 28 days before the window, each with at least 5 readings. Higher is fitter. A change of 12% of where you started counts.

Endurance fitness sets your training base now against its value about 12 weeks ago, and needs at least that much history. The older value is the nearest scored day at or before that date, and no more than 3 weeks earlier. A change of 2 points or more reads Rising or Falling, and less reads Steady.

In 10 runners who responded to a 9-week training programme, resting heart rate averaged over a week tracked 10-km running performance better than a single day's reading (HRV tells the same for HRV). Aera averages over 28 days, its own choice, not taken from a study.²

One review says a change should be read against the measure's error and the smallest change that matters. A cut-off is one way to apply that idea, but every one above, and the length of the window, is Aera's choice and not taken from the review or any other study.³

4

What is the level for your age?

Cardio fitness can show where your estimate sits among people your age. It is context, and the word still comes from the change.

When Apple Health has your sex and your age, from 20 to 79, the Cardio fitness card shows five steps instead of a line: Low, Below average, Average, Above average and High. Its sentence reads, for example, Average for your age. The word on the card is still Rising, Falling or Steady.

The steps come from FRIEND, a US registry of 7,783 maximal treadmill tests in men and women aged 20 to 79 without cardiovascular disease. Each step covers one fifth of people of your age and sex.⁴

The registry used a treadmill, so Aera multiplies the watch value by 1.10 before it looks up your step. That factor is Aera's choice, not taken from a study.

The watch estimates VO2 max and does not measure it. In a 2026 lab test it put only 14% of participants in their true band. In a smaller test of 19 people it read high in those with poor fitness and low in those with excellent fitness (VO2 max tells the tests).^5,6

5

When does it show nothing?

Too few readings show Learning, a strength-only season keeps just Resting heart rate, and older comparisons need Premium.

A card that lacks readings sits under Learning with a count. Cardio fitness counts estimates out of 6 and needs them spread over at least 28 days. When all are in but too close together, the card says when it will be ready.

Effort counts passes out of 5, Resting heart rate counts nights out of 21, and Heart rate recovery counts readings out of 5. Endurance fitness reads Fills in as you train until it has the history it needs.

If you have workouts in the last 12 weeks and every one is strength training, Cardio fitness, Effort and Heart rate recovery are left out, and only Resting heart rate is kept. Endurance fitness is not filtered.

The last 30 days are free. A free reader whose 12 weeks reach further back sees the cards in a fixed order, headed Last 30 days. They carry no word and no earlier figure, a plain sentence, and the last 30 days drawn.

6

What can't it tell you?

A change is two readings set side by side, not proof of what caused it. Each reading also carries its own error.

One review argues that heart rate measures cannot inform on every aspect of fatigue and performance, and that a change needs its training context. A trend card tells you a reading moved, not why.³

In a test of 39 adults, the watch's resting heart rate matched a chest strap closely on average, with a typical single reading off by about 4 beats (HRV tells it).⁷

The VO2 max estimate carries more error. In two lab tests it missed by about 13% on average and read low overall. The 2026 authors say that tracking change over time still needs to be tested.^5,8

Your resting heart rate may also move less than a friend's. In a review of 191 trials in healthy people, the drop after exercise was larger in people who began with a higher rate and smaller in older people (Resting heart rate tells it).¹

When your resting heart rate has risen, its page can show what your last four weeks would read without the sick, short-night and hard-workout mornings. The trend itself leaves no night out.