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ACWR, monotony and strain

The ratio everyone quotes, what it actually tells you, and what it does not.

Once you have daily load, you can ask a better question than how much. You can ask how much, compared to what this athlete is used to.

Acute and chronic load

Acute load is the recent dose, normally the trailing 7 days. Chronic load is the accumulated base, normally the trailing 28 days. Chronic load is a rough stand in for fitness. Acute load is a rough stand in for fatigue.

ACWR = acute load / chronic load

A value near 1.0 means this week looks like the last month. Above 1.0 means the athlete is doing more than their recent normal.

Two ways to calculate it

The simple method uses rolling averages: the 7 day mean divided by the 28 day mean. It treats a session 27 days ago as mattering exactly as much as yesterday, which is obviously wrong.

The better method is an exponentially weighted moving average, or EWMA. It decays the influence of older sessions. The decay constant is lambda = 2 / (N + 1), so a 7 day window gives about 0.25 and a 28 day window about 0.069. Athlivate defaults to EWMA and shows which method produced the number on screen.

ACWR	Label	What it suggests
Below 0.8	Low	Undertrained relative to recent base, or coming off a break
0.8 to 1.3	Target	Progressing within a familiar range
1.3 to 1.5	Caution	Rising faster than the base supports, worth a look
Above 1.5	High	A clear spike, usually a tournament or a jump in volume

Note

ACWR needs at least 21 days of data before it means anything, because the chronic denominator has to be real. Before that the product says building baseline and shows no number. A ratio built on five days of data is noise with a decimal point.

Be honest about the evidence

ACWR became popular fast and the evidence has not kept up. A season long randomised trial in youth football found no reduction in injuries from planning by ACWR. A study in junior tennis found no association between swing count ACWR and injury. There are also real statistical criticisms of the ratio itself, including spurious correlation between a numerator and a denominator that share data.

So treat it as a conversation starter, never a verdict. The right sentence is load has jumped, let us look at why. The wrong sentence is this athlete has a 40 percent injury risk. Athlivate will never print the second one.

Monotony and strain

Two athletes can have the same weekly total and very different weeks. One trained hard on three days and rested on four. The other did the same moderate session every single day. Monotony captures that difference.

Monotony = mean daily load / standard deviation of daily load

High monotony means a flat week with no real variation. Variation is what lets tissue recover and adapt.

Strain = weekly total load x monotony

A big week that is also flat scores worse than a big week with genuine hard and easy days.

Scope

This page is education, not medical advice. If something hurts, or a pattern worries you, book an assessment with a physiotherapist. They own that decision.

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