Training Monotony and Strain Calculator

Weekly total load tells you how much you did. Monotony tells you whether the week had a shape. Two athletes can log identical totals with completely different risk profiles, and this is the pair of numbers Carl Foster proposed to make that difference visible. Enter each day’s load — session RPE units or TRIMP points, but the same one all week.

The two formulas

Monotony = the week’s mean daily load ÷ the standard deviation of the daily loads.

Strain = the week’s total load × monotony.

The logic is compact, and a worked pair shows it. Take a week of 300, 310, 295, 305, 300, 290, 300 — total 2,100, standard deviation 6.0, monotony 50. Now redistribute the same 2,100 into 500, 100, 400, 600, 100, 300, 100: the standard deviation becomes 192.7 and monotony drops to 1.6. Same volume, opposite verdict. Strain then multiplies the total by that ratio, so it only gets large when the volume is high and the week is flat — exactly the pairing Foster’s original work associated with illness and poor performance.

Note that rest days are part of the calculation, not gaps in it. Entering a zero for Sunday raises the standard deviation and lowers monotony, which is the arithmetic saying what a coach would say.

Reading the numbers

• Monotony below 2.0: the week has clearly harder and easier days.
• Monotony at or above 2.0: low day-to-day variability. Applied studies of team sport use 2.0 as the dividing line between higher and lower variability within a microcycle.
• Strain: watch its trend rather than its level. Published work on youth football cites values above 6,000 AU as associated with greater injury risk and non-functional overreaching — a reference from that population and that load metric, not a universal number.

Treat all three cut-offs as field conventions inherited from team sport monitoring, where the daily load figure is session RPE for a full squad. They are useful reference points for reading your own trend, not diagnoses.

What to change when monotony is high

Nothing about the weekly total, first. The whole appeal of the metric is that it identifies a distribution problem, and distribution is cheap to fix: convert one middling day into a genuinely easy one and another into a genuinely hard one. The total holds, the standard deviation rises and monotony falls.

If the total itself is what has jumped, that is a different problem, and it belongs to what is training load rather than to this calculation.

Where the daily numbers come from

Feed this calculator from either method: the session RPE calculator if you rate effort, or the TRIMP calculator if you record heart rate. Both produce a comparable-to-itself daily figure. What they cannot do is be mixed — a week of four TRIMP points and three session RPE units produces a standard deviation that means nothing at all.

This content is informational and does not replace guidance from a coach or clinician.