Glossary
Fitness and freshness
Fitness is a rolling average of your training load, usually over 42 days. Freshness is fitness minus a shorter 7-day average, so it goes negative in hard weeks.
What it is
Two lines drawn from the same data.
Fitness is a long rolling average of your daily training load. Most systems use 42 days. It rises slowly when you train more than usual and falls slowly when you train less.
Freshness is fitness minus a short average, usually 7 days. When this week was harder than the last six, freshness is negative. When you taper, it climbs.
| Line | Window | Rises when |
|---|---|---|
| Fitness | ~42 days | you train more than your recent average |
| Fatigue | ~7 days | you trained hard in the last week |
| Freshness | fitness − fatigue | you back off |
What it is not
It is not a measure of your fitness. It is a measure of how much you have been training. Those track each other loosely and come apart often.
This is the source of the most common complaint about the metric: _my fitness score fell while I got faster_. Both things can be true. If you replace long easy runs with short sharp ones, your load falls and your 5K time improves. The long version of that answer is here.
It is also not comparable between people. The number depends on how your intensity is measured and on your own baseline.
What moves it
- Volume, mostly. Long runs raise fitness more than hard short ones.
- Consistency. A missed week costs more than a great single session gains.
- Your zones. If load is heart-rate based, wrong zones bend both lines.
- Nothing you did today. With a 42-day window, one run moves fitness by about 2%.
When to ignore it
Ignore freshness during a taper, unless you are using it to confirm the taper is working. A positive number there is the plan, not a warning.
Ignore fitness after any break longer than a fortnight. It is decaying at the rate of a formula, not at the rate of your body.
Ignore both if your heart-rate data is unreliable. Two lines drawn from bad inputs are still bad inputs.
Sources
- Banister EW, Calvert TW. Planning for future performance: implications for long term training. Can J Appl Sport Sci 5(3):170-176, 1980 primary
- Busso T. Variable dose-response relationship between exercise training and performance. Med Sci Sports Exerc 35(7):1188-1195, 2003 primary
- Coggan A, Allen H. Training and Racing with a Power Meter — the CTL/ATL/TSB formulation reference