Monotony and training strain in Analytics

Two different things are called "strain"

Wearables like Whoop report a day strain on a 0 to 21 scale: how hard your heart worked over a whole day, sleep and daily life included. IntervalCoach only shows that number when a wearable that provides it is connected.

The strain in Analytics under Monotony & Strain is a different metric: training strain from Carl Foster's monotony model. It is not on a 0 to 21 scale. Values in the hundreds or low thousands are normal for a heavy training week.

How training monotony is calculated

Monotony looks at your last 7 days of training load (TSS) and asks how uniform it was:

Monotony = average daily load ÷ standard deviation of daily load

Seven similar days give a high monotony. A week with clear hard days and clear easy or rest days gives a low monotony. Above 1.5 we flag it as elevated, above 2.5 as high, because uniform loading with little variation is associated with overuse and illness risk in Foster's research.

During a taper or race week, low and uniform load is intentional, so monotony is not treated as a warning there.

How training strain is calculated

Strain = monotony × total 7-day load

So strain rises with both volume and uniformity. A big week with little day-to-day variation scores highest. Example: 700 TSS over the week with a monotony of 0.5 gives a strain of 350.

How to read it

Treat strain as an overuse warning rather than a target. The absolute number depends on your usual volume, so compare it to your own recent weeks. The useful signals are the trend and whether monotony is flagged elevated or high. If it is, the fix is usually more variation: keep the hard days hard and make the easy days genuinely easy, or add a rest day, rather than cutting volume across the board.