CTL (Chronic Training Load)

Chronic Training Load (CTL) is a 42-day exponentially-weighted average of your daily TSS. It is widely treated as a proxy for fitness.

How it is calculated

Each day, CTL = previous CTL × (1 - 1/42) + today's TSS × (1/42). The recent days count slightly more than older days, but the overall view is six weeks deep.

Why it matters

CTL changes slowly. That is the point — it shows the cumulative load your body has adapted to absorb. A CTL of 70 means you have averaged ~70 TSS per day over six weeks.

• Building CTL = building fitness (when load matches your capacity to absorb it).
• Falling CTL = detraining.
• Flat CTL while trying to build = you are not actually doing more work.

Common misconceptions

• CTL is fitness the way the model defines it. It does not know about quality, just quantity.
• CTL rises slower than it falls. A two-week break costs more than two weeks to rebuild.
• A higher CTL is not always better — context matters. 80 CTL of pure endurance is different from 80 CTL of intervals.

Related concepts

ATL, TSB, TSS.