Workout effort

1

What does Workout effort show?

How hard a session felt, as a whole number with a word beside it. Your own rating always comes first.

Open a workout and look for Perceived effort. It shows one number from 1 to 10 with a word beside it, over a slider of 10 steps. Tap or drag along the slider to rate the session. Once you rate it, or Apple Health already holds a rating for it, the page reads "You rated it 7 of 10, Hard." With no rating anywhere, it says "Drag to say how hard it felt."

Apple names four levels of effort: Easy, Moderate, Hard and All Out. Aera uses those words and sets them on the steps like this: Easy for 1 to 3, Moderate for 4 to 6, Hard for 7 and 8, and All Out for 9 and 10.

A hollow ring on the slider marks the estimate. Until you rate, the figure shows the estimate too, with the word Watch or Aera beside it. The ring stays after you rate, because the estimate is worked out as if you had not rated, so your rating never hides it.

Your rating is saved on the session. On your first rating Aera asks permission to save it to Apple Health too. If the session is in Apple Health and you allow it, Aera writes it a second after your finger settles and replaces the one it wrote before.

2

Why does your own rating come first?

Because a rating of how it felt measures effort in its own right. Aera never replaces yours with an estimate.

The idea is old. In 1982 Borg described a scale for ratings of perceived exertion, a number you give for how hard work feels. He called such ratings important complements to physiological measurements.¹

A German study tested the idea in 2,560 men and women. They did step-by-step exercise tests on a treadmill or a bike, and at the end of each step gave a rating while their heart rate and blood lactate were measured. Ratings were strongly linked to both: 0.74 with heart rate and 0.83 with lactate, where 1 would be a perfect link.²

Ratings of a whole session were tested too. In a 2001 study, people cycled steadily and in intervals, or practised basketball. A score from one rating of the whole session moved consistently with a score from heart rate. A 2017 review of 36 studies found this session rating method valid and reliable in several sports, for men and women of different ages. Training load tells what is done with it.^3,4

These studies support a rating as a sound measure of effort. Putting yours first is Aera's own choice. The German study used Borg's older scale, from 6 to 20, so none of this tests the scale Aera uses.²

3

Which number shows when you have not rated?

The first that exists: the middle of your past ratings, then your watch's estimate, then Aera's own guess.

Aera goes down a list and stops at the first source it finds. First comes your own rating: the one you tapped on the page or, failing that, the one Apple Health holds for the workout. Without one, Aera takes the middle of your last 5 ratings, then the estimate your watch made, the one Aera reads from Apple Health, and last its own guess from the workout.

The middle of your last 5 ratings is the one left in the centre when you line them up from lowest to highest. Only ratings saved on your sessions count, never an estimate, so the middle cannot feed on itself. They must be for the same kind of session in the 30 days before this one, and each is rounded to a whole step first. For strength, Aera looks at your last 8 sessions of that kind instead of the 30 days. The 5, the 30 days and the 8 are Aera's own choices, not taken from a study.

When Aera's estimate is that middle, the page says "Aera's is the middle of your last 5 ratings." and a band on the slider spans those ratings, from lowest to highest.

A sport you have never rated starts with your watch's estimate or Aera's guess. Rate 5 sessions of it within 30 days and the middle takes over, then moves with you as you rate more.

4

How does Aera guess from the workout?

From your average heart rate, how long you went and the energy you burned, blended into one number.

Aera's guess blends three parts. Your average heart rate counts for 40%, how long you went for 30% and the energy you burned for 30%. The weights and the limits below are Aera's own choices, not taken from a study.

Heart rate is read on one fixed range, from 80 to 190 beats a minute, the same for everyone. A peak above 175 adds a small extra, so hard efforts and intervals read higher.

Time is read as a share that climbs fast at first and then flattens, so the second hour adds less than the first. Each kind of session also stretches or shrinks the minutes: a minute of walking or yoga counts for less than a minute of running or high-intensity intervals.

Energy is read as kilocalories per minute, a stand-in for how intense the work was. A rate of 14 or more fills this part.

The three parts add up to a share of the full range, which Aera stretches onto Apple's 1 to 10 scale. The page then rounds it to the nearest whole step.

5

When does it show nothing?

When there is no rating, no estimate from your watch and no heart rate for Aera to read. The slider stays.

Aera's own guess needs a heart rate. A workout with no average heart rate, no watch estimate and fewer than 5 ratings of that kind shows no estimate. You see only the slider and the line "Drag to say how hard it felt." Your own rating still counts the moment you give it.

If the heart rate is there but the energy reading is missing, the energy part is filled with a small fixed value, not skipped.

For a session recorded without a heart rate, the workout page says that a watch or a chest strap worn while you train fills in heart, effort and zones.

6

What can't it tell you?

How the session felt to you, unless you say. A felt rating can drift, and Aera's own number is a rough guide.

A felt rating is not a clean measure either. In a small 2009 experiment, 16 people cycled to exhaustion after 90 minutes of a demanding mental task and, on another day, after 90 minutes of watching documentaries. After the mental task they rated the effort higher and gave up sooner, while the response of their heart and lungs stayed largely the same. Tiredness of the mind can change the number.⁵

Aera's guess has no feeling in it. Its heart rate part uses one fixed range for everyone, not yours. A review of ways to set intensity notes that even the same share of each person's own maximum heart rate does not necessarily put people at the same intensity. A range fixed for everyone can only be a rough guide. Intensity tells more.⁶

So read Aera's number as a rough guide and your rating as the one that counts. Either describes a single session. For training across days, see Cardio load.