Fatigue Index Calculator

How to calculate Fatigue Index?

The Fatigue Index is a measurement of the power drop in anaerobic tests. It reflects the rate at which power declines from the peak output to the lowest output during a maximal effort sprint, indicating an athlete's anaerobic endurance.

FI (%) = ((Peak Power - Lowest Power) / Peak Power) × 100

Using the Fatigue Index: an example

A standard 30-second sprint test is typically performed on a cycle ergometer. The athlete starts at maximum intensity, and power output is tracked continuously from the first second to the last.

Step-by-step calculation:

1. Record peak power at the start (e.g., 900W)
2. Record lowest power at the end (e.g., 500W)
3. Calculate difference (400W)
4. Divide by peak and multiply by 100 to get 44.4%

Frequently Asked Questions

What is a normal fatigue index?

Typical values range from 30% to 50% for trained athletes. While a lower index suggests better endurance, elite sprinters often have higher indices because their peak power is exceptionally high.

Why is this metric important?

It helps coaches understand if an athlete needs more speed endurance or power training. A high fatigue index might indicate a need for better metabolic conditioning, whereas a low index with low peak power suggests a need for strength and explosiveness.