Chronic training load (CTL)
Chronic training load (CTL) is an exponentially weighted average of your daily training stress over roughly the last 42 days. It's often labelled 'fitness': a higher CTL means you have been handling more training for longer.
How CTL works
Each day's training stress score is blended into the average, with recent days weighted more than older ones. Because the time window is long, CTL rises and falls slowly — one big week barely moves it, while a consistent month does.
How fast to build it
The weekly rise in CTL is called the ramp rate. Building too quickly raises the risk of illness, injury and burnout; many coaches keep it to a few points a week, with recovery weeks that let it level off. CTL measures training load, not race-day performance, so a higher number isn't automatically a faster athlete.