Energy

1

What does Energy show?

A running level that your night fills and your day draws down, with a word beside it.

On the Timeline page, Energy sits at the top: a figure from 1 to 100, a word beside it and a line under them. Home's Your day section can say the same line.

Four words set the level. Full starts at 80, Plenty left at 50, Some left at 25, and under 25 it reads Running low. Aera chose these cut-offs; they are not taken from a study.

2

What charges it?

Sleep charges it most, and calm stretches of the day add a little.

A night charges against your sleep need, not against its own length, because need differs from person to person. In one lab study, the gap between a person's own best sleep and what they usually got tracked sleepiness more closely than hours slept did. That study did not test Energy. A night that meets your need charges up to 80 points, and a shorter night charges less. Where Aera has no need for you yet, it uses 8 hours. It uses the latest need it has worked out for you, for every night in the run.¹

A heart that runs high while you sleep reads as more stress, and the more stress a step reads, the less it charges. Hard exercise can raise the night's heart rate. In ten men, the average heart rate at night rose to 109% of the rest-day level after moderate endurance exercise, and to 130% after a marathon.²

Calm time while awake charges it a little. A waking step charges, rather than spends, when its stress reads under 20, at a pace of 15 points over a 16-hour day. The calmer the step, the more it charges.

3

What spends it?

Waking time spends it, faster while your heart runs high, and workouts spend it by their effort.

Waking time spends at a pace of 60 points over a 16-hour day. Your stress in each step speeds that up or slows it down. The readings are the ones behind your Stress score, with those from sleep and from the time after a workout added.

Moving spends too, even without a workout. A reading taken while you move counts as 45 points more stressed, up to 100.

A workout spends at 50 points over 16 hours. When it has an average heart rate, its stress comes from that: 100 beats a minute reads 65, and 147 or more reads 100.

A waking step with no reading at all spends at 0.7 of the stressed pace. None of these amounts is taken from a study, and the 45 is Aera's own choice, tried on real days of readings.

4

How does the level move?

In small steps, with a brake near the top and near the bottom.

The day is cut into steps of 6 minutes. In each, Aera averages the readings, decides whether you were asleep, working out or awake, and moves the level up or down. The very first step starts at 50.

Charging slows above 60, and spending slows below 40. So the level eases toward the ends rather than rushing to them, and it never leaves the range of 1 to 100.

Aera runs the battery without a break from 28 days before the week on screen, a lead Aera chose. Each day starts from the level the day before ended on. A day's level counts from 3 days after the first day with anything to read, once the first guess has washed out.

5

What do the lines under the figure say?

How you stand against your usual, what cost the most, and what tonight may leave.

Under the word, the page sets today's level against the same clock time on your earlier days. It takes the middle of up to 14 of them, once 7 are in. Above your usual for this hour means 10 points or more over, Under means 10 or more under, and About is in between. A past day says how far above or below it ended. These limits are Aera's choice, not a study's.

The line can then name what cost more than on your usual days: "mostly from" it when you are under, "though" it cost more when you are not. It names one kind of time, such as the tense stretch, time on your feet, last night or a workout. That kind must have taken the level at least 5 points further down than the same hours on those days. Aera set that 5-point gap.

Those kinds have plain edges. Tense hours are still hours when stress sits at 40 or more, the Raised line on the Stress page. Calm hours are still hours under 20. Time on your feet is a step where most readings came while you moved. Aera chose these edges.

Hold your finger on the chart and the line turns to that moment. It gives the time, then what was happening: Charging while you slept, Calm enough to charge, Up and about, spending, or During your walk. In the morning, the headline says whether you woke charged after a short night, a full one or a restless one.

Further down, Last four weeks names the kind of time that spent the most an hour, and what gave back: calm waking hours first, otherwise sleep. Each comes with its points an hour. A kind needs 3 hours behind it before it is named, a limit Aera set. In the evening, the headline looks ahead: it plays out an ordinary evening and a full night of your need from your usual bedtime. It is a projection, not a promise.

An older day's Energy sits behind Premium. Which days count as older is Aera's choice.

6

When does it show nothing?

Before the run has enough to go on.

A day needs a recorded night or at least 20 still heart readings. Without them, or before the run has warmed up, you see the day without a level. The comparison with your usual stays out until enough earlier days are in.

7

What can't it tell you?

How energetic you feel. It is a model of your day, and nothing outside the app checks it.

Energy is an estimate, not a measurement. The way it adds things up follows a method used by a fitness app, with changes of Aera's own. It is not a model tested against people.

If you feel full of energy and the page says Running low, trust yourself.