ATL (Acute Training Load)

ATL is the 7-day exponentially-weighted average of your daily TSS — the fatigue side of the fitness/fatigue model. ATL responds fast: a hard block drives ATL up quickly, and a few easy days bring it back down. It's why you feel flat two days after a crusher session.

ATL_today = ATL_yesterday + (TSS_today − ATL_yesterday) / 7
    (EWMA with a 7-day time constant)

The 7-day constant approximates the time course of acute fatigue — most of the residual fatigue from a training day is gone within a week, though some adaptations and inflammation persist longer.

ATL alone isn't very useful — it's how ATL compares to CTL (= TSB) and how fast ATL is changing that carries information about your readiness. A sudden ATL spike with flat CTL is the classic overload block signature; the taper is engineered to pull ATL down while preserving CTL.