Strava Fitness Score Explained — What Does CTL Really Mean?

By WattWorks · April 13, 2026 · 9 min read

Millions of Strava users watch their "Fitness" score rise and fall every day — but most don't understand what it actually measures. Strava calls it "Fitness", but behind it lies a scientific model used by professional teams worldwide: CTL (Chronic Training Load).

Understanding your Strava Fitness Score lets you build it deliberately, avoid overtraining, and plan your race season intelligently. Here's everything you need to know.

What Is the Strava Fitness Score?

Strava calls it "Fitness" — sports science calls it CTL (Chronic Training Load). It's not a subjective measure, but a mathematically calculated number that reflects your long-term training load over the past 42 days.

Measures long-term training load over 42 days
Calculated from the TSS (Training Stress Score) of each session
Rises slowly (weeks), falls relatively quickly (days)
Originally developed by Andrew Coggan and Hunter Allen

CTL(today) = CTL(yesterday) × e^(-1/42) + TSS × (1 - e^(-1/42)) → Exponentially weighted average — recent sessions count more

What Do the Three Strava Values Mean?

Strava's "Fitness & Freshness" chart shows three curves. Each one corresponds to a scientific concept:

Strava Name	Science	Time Window	Meaning
Fitness	CTL	42 days	Long-term training adaptation
Fatigue	ATL	7 days	Short-term tiredness
Form	TSB	—	Freshness = CTL minus ATL

    Green Form = ready to perform: When your Strava Form is green (positive), you're recovered and ready for good performances. When it's red (negative), you're fatigued — but actively building fitness.
  

Why Is the Strava Fitness Score Important?

Shows whether your training is actually working
Helps you detect overtraining early
Forms the basis for race planning (tapering)
Gives you a concrete number instead of gut feeling

Training purely by feel means never knowing if you're overloading, undertraining, or hitting the right zone. CTL makes it measurable.

What Is a Good Fitness Score?

Level	CTL (Fitness)	Meaning
Beginner	20–40	Regular training, building base
Recreational	40–60	Good base, gran fondos achievable
Intermediate	60–80	Structured training, race-ready
Competitive	80–100+	High performance, high volume
Professional	100–150+	Pro sport level

Why Does Strava Show Less Than WattWorks?

Your Strava Fitness Score is often lower than your actual fitness level. The reason: Strava only calculates CTL from activities that exist directly in Strava.

FIT file uploads from Garmin or Wahoo devices are often missing
Indoor sessions on a trainer may not sync automatically
Manual activities without power meter data have no TSS

WattWorks combines all sources — Strava sync and direct FIT file uploads — giving you a more accurate picture of your true fitness.

How to Build Your Fitness Score

Building CTL takes time and consistency. Key principles:

Consistency beats intensity — 5 easy days beats 2 hard days
Safe CTL build: maximum 5–7 points per week
Building too fast increases injury and overtraining risk
Rule of thumb: weekly TSS ÷ 7 = your long-term CTL target

    Practical example: Consistently training at 400 TSS/week will eventually stabilize your CTL around 57. At 600 TSS/week, the equilibrium CTL is approximately 86.
  

WattWorks Shows Your Real Fitness Score

All activities combined — Strava + FIT files. CTL, ATL, TSB in real time. No manual calculations, no Strava subscription needed.

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Free · No subscription · FIT upload or Strava sync

Frequently Asked Questions About the Strava Fitness Score

What's the difference between Strava Fitness and CTL?

They're the same thing — Strava simply calls CTL (Chronic Training Load) "Fitness". The calculation formula is identical: an exponentially weighted average of daily TSS over 42 days.

How quickly does the Strava Fitness Score rise?

CTL rises slowly — that's by design. With consistent training you can build roughly 5–7 points per week. Faster builds significantly increase injury risk. Going from CTL 30 to CTL 60 takes 4–6 months with good structure.

What happens to your Fitness Score when you stop training?

CTL decays with a half-life of ~42 days. After one week without training you lose roughly 8–10% of your CTL value. After 4 weeks that's 25–30%. The good news: previously built CTL recovers faster than it was originally built.

Why is my Fitness Score dropping even though I'm training?

CTL is calculated from your daily average over 42 days. If your current TSS is lower than your 42-day average, CTL drops — even if you're training. A recovery week will always cause a slight CTL decline.

How high should my Fitness Score be before a gran fondo?

For a typical gran fondo (100–160km) a CTL of 60–80 is recommended. For longer events like the Ötztaler (238km, 5,500m elevation) aim for at least CTL 70–90. Equally important: your TSB should be +5 to +15 on race day (tapering).