Cardio load

1

What does Cardio load show?

How much work your heart did in your workouts, and one word for how your last week compares with your usual.

Aera adds up the heart work of your workouts, day by day. It keeps two running averages of that daily figure: your last 7 days, and your usual, which follows about the last six weeks. The screens call the reading Training load. This article calls the daily heart work behind it Cardio load.

Home and the widget give the week one word. A workout's page has a Training load chapter. It says what the 7 days to that workout came to against your usual, and draws the 14 days that ended with it. Fitness draws your usual as its base on the Endurance fitness page (Fitness trends tells about it).

Home and the widget use six words: Below base, Holding, Building, Tapered, Above range and Load spike. A workout's page says Steady for Holding, Below your usual for Below base and Climbing fast for Above range. It also says usual where Home says base.

The Cardio load tile on a workout's own page is a different figure. It comes from the workout's energy, or from its effort score, not from the heart rate sums described here. They usually will not match.

2

What goes into it?

Your workouts, each scored from its length and your heart rate. Steps and unlogged walks add nothing.

For each workout, Aera takes its average heart rate and asks how far it sits between your resting heart rate and a top heart rate of 190. That share is your heart rate reserve in use. The workout's minutes are weighted by it, and hard minutes count far more than easy ones.

Why the reserve and not a plain share of top heart rate? One review notes that the same share of top heart rate does not necessarily put people at the same intensity above their resting level. Strain tells the studies behind this score.¹

The weights come from a method worked out on men, and Aera applies them to everyone. That is a known limit.

A workout needs an average heart rate above 60 beats a minute, over more than a minute. Without that, Aera falls back on the workout's energy, or on its type and length, and counts that estimate at 35 percent.

Walks, hikes, yoga and similar gentle sessions count at 60 percent. That is Aera's own choice. Steps and walks you did not log as a workout add nothing, which is one way this differs from Strain. A workout that two sources both recorded counts once.

3

Why is the top heart rate a flat 190?

Cardio load keeps one fixed top heart rate for everyone. Strain has moved to your own.

Strain measures effort against your own top heart rate: one you typed, or an estimate from your age and your highest recorded beat (see 220 minus your age). Cardio load does not. It uses 190 for every workout, and lifts that only when the workout's own highest heart rate is above 190.

So if your real top heart rate is lower than 190, the same effort reads low here. If it is higher, it reads high. A session can therefore score differently here and on the Strain page.

Aera kept the flat ceiling on purpose. The size cut-offs for a usual, set out below, were set on that scale from one person's year of data. Moving to your own ceiling means setting them again.

One more difference. Strain ignores a peak above 220 beats a minute as a sensor spike. Cardio load makes no such check itself, so a very high peak would lift the ceiling and lower that workout's load.

4

How do days become your last 7 days and your usual?

Each day's load feeds two running averages, one about a week long and one about six weeks long. Newer days count more.

A day's load is the sum of that day's workouts. Aera keeps two running averages of it. Your usual, called the base on Home, follows about the last six weeks. Your last 7 days follow about the last week. In both, newer days count more than older ones.

Each day, your usual closes one forty-second of its gap to that day's load, and your last 7 days close one seventh. Both start from zero, so a new usual takes weeks to fill.

The 7 and the 42 are fixed for everyone, not fitted to you. In one study of nine elite swimmers, the fitted fade times of a model of this kind came with wide margins (Training load tells it).²

A workout's page draws the 14 days that ended with it, with a band around your usual behind the line.

The band's top edge sits at 130 percent of your usual, a little under the 135 where Above range starts. So a line just above the band can still read Building.

Room to train reads the same daily load, but builds its own average from it. Room to train tells how.

5

How does a number become a word?

Your last week divided by your usual picks the word. Smoothing keeps one odd day from changing it.

Divide your last week by your usual. Under 80 percent reads Below base. Up to 100 percent reads Holding.

Up to 135 percent reads Building. From 135 percent up it reads Above range.

Tapered is checked first. It needs a strong usual, 30 or more, and a last week at least 15 points under it, as of yesterday. It marks an easy stretch on a strong usual.

Under a usual of 18 the rules change. A ratio of 135 percent or more reads Building, never Above range. Twice the usual or more reads Load spike.

When your usual has itself fallen 10 percent or more over 28 days, Holding reads Below base instead. That is Aera's own rule.

Aera averages the ratio over 5 days, and a new word has to hold for 3 days before it replaces the old one. A jump of two places along the ladder, or a Load spike on a light usual, shows at once. Your first word shows straight away.

These cut-offs are Aera's own choices. They describe your weeks and are not proven thresholds.

6

When does it show nothing, or something else?

Until your usual is big enough there is no word. On Home, time off turns Below base into Resting.

A usual of 5 or less is too small to read. Home says Still learning, and a workout's page shows no word.

A workout's page also needs 7 days of load before it draws its chart. Until then it says roughly how much that day raised your last 7 days, or that your usual appears after your first weeks of outings.

Mark a day as sick, injured or on a break and Home and the widget read Resting instead of Below base, for that time and a week after. Travel does not count. Time off does not change the numbers, only the word.

Home shows a Training load card on the day your word changes. It skips the card when the word turns to Below base while you are on time off.

The word follows a 5-day average, so on some days it lags the numbers. When it does, a workout's page shows the numbers and leaves the word off.

7

What can't it tell you?

Anything your heart rate does not show, and whether a week is wise for you. It compares load with load.

The daily load reads each workout's average heart rate. Hard minutes count far more than easy ones, so a session of hard bursts with rests between can score lower than its minutes taken one by one. Work that keeps your heart calm, such as lifting, registers lightly.

A wrist also reads heart rate less well in motion: in a test of wearables, absolute error during activity was on average 30% higher than at rest (How a watch measures you tells why).³

Nothing here sees your sleep, illness or soreness. Room to train weighs sleep beside your training.

A 2020 paper argued there is no evidence for using a ratio like this one to plan training or lower injury risk (Training load tells it). So the word is not an injury warning. It says how your recent load sits against your usual.⁴