Readiness: what CTL, ATL and TSB mean

The readiness ring: how am I today

The 0–100 number combines factors — sleep, HRV, resting heart rate and others — each compared against your personal norm over the last 60 days. The green zone on a factor chart is your norm; the further today’s marker sits from it, the harder the factor drags readiness down. If there are no overnight metrics (your watch did not sync), readiness is honestly not computed — better press the manual refresh: everything on the watch is pulled in and readiness is recalculated immediately.

Fitness (CTL): slow capital

CTL is your accumulated training over roughly the last six weeks. It rises slowly and falls slowly — this is what stays with you between seasons. The higher the fitness, the more load your body handles and the higher the plan’s ceiling.

Fatigue (ATL) and freshness (TSB)

ATL is the load of roughly the last seven days. It responds fast: a couple of hard days push it up straight away. TSB = fitness − fatigue. A negative number means you are in the hole: you have banked load you have not yet absorbed. For a race, freshness is deliberately brought into positive territory — the target window is +5…+15: the taper cuts fatigue, fitness dips slightly, and the legs run.

The corridor (ACWR): a pace gauge, not a verdict

ACWR is the ratio of your fresh weekly load to the level you are used to over the past month and a half. The corridor bounds are percentiles of your own history, not textbook constants: “above the corridor” means “a sharp spike for you”. It is a ramp-rate indicator, not an injury forecast — but living above the corridor for weeks is unwise.

How to use all of this

• 30 days — the scale of working weeks: the load → recovery rhythm. The month’s deepest freshness trough at the end of a hard block is normal — just do not live there for weeks.
• 90 days — whether the load is being absorbed: is fitness rising or are you spinning your wheels?
• 180 days — the season: a long CTL rise with undulating deloads is the sign of a healthy cycle.
• The base: thresholds (LTHR, weight) are the reference for zones and fitness. Keep them current: Health → Thresholds. Chart empty? Connect your watch — fitness cannot be computed without workouts.