Training load simulator
Same formula as the Overload app
This training load simulator projects fitness, fatigue and form from a weekly load plan, the same three metrics coaches use to schedule hard and easy blocks. Enter a training load figure for each day of the week, choose how many weeks to repeat that plan, and the tool runs Banister's exponentially weighted model to show where your form lands by the end of the period, with a chart of every day along the way.
Weekly plan
End-of-period form (TSB)
-11.4
Negative TSB means you're carrying fatigue from recent training.
How it works
Fitness (CTL) and fatigue (ATL) are both exponentially weighted moving averages of daily training load, following Banister's 1975 impulse-response model as popularized by Allen & Coggan's performance management chart. CTL uses a long 42-day time constant so it rises and falls slowly, while ATL uses a short 7-day time constant so it reacts to the last week of work.
Each day, both averages move a fraction of the way from their previous value toward that day's load, where the fraction (alpha) equals 1 minus e to the power of minus 1 over the time constant. Form (TSB) is simply yesterday's fitness minus yesterday's fatigue, so it turns positive when a block of easier days lets fatigue fade faster than fitness does.
Repeating the same weekly plan for more weeks lets you see whether that pattern is sustainable: a rising CTL with a TSB that keeps diving deeper each cycle signals a fatigue plan, while a TSB that recovers toward zero between blocks signals a plan built for lasting fitness gains.
Frequently asked questions
What is a good TSB before a race?
Many endurance athletes aim for a TSB somewhere between 0 and +20 in the days before a key event, reached by tapering training load so fatigue drops while fitness holds. This simulator lets you test whether a given weekly plan reaches that range by race week.
Why do CTL and ATL use different time windows?
Fitness builds and fades slowly, which the 42-day CTL constant captures, while fatigue from recent sessions clears within days, which the short 7-day ATL constant captures. The gap between the two time windows is what makes TSB a useful signal of current form.
Can this replace tracking my real training load?
No, it only projects a repeating hypothetical plan forward to show a trend, not a forecast of any specific day. Overload computes CTL, ATL and TSB from your actual logged sessions, updating every day rather than assuming the same week repeats indefinitely, so its numbers track what you actually did.
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Overload computes your real fitness, fatigue and form
Overload calculates CTL, ATL and TSB from your real sessions every day, no manual plan required. Free on iOS and Android.