How to calculate threshold power and different zones

An individual’s Functional Threshold Power (FTP), also known as Threshold Power, is a representation of one’s ability to sustain the highest power output possible over 45 to 60 minutes; and can be determined for an athlete from any level of experience or training. Having regular assessments of FTP can give you a clear indication whether improvements are being made from training and can provide updated ‘training zones’ for sessions.

There are two key ways to determine your FTP on a Wattbike:

  1. 20-minute threshold test: most Wattbikes will have a pre-programmed 20-minute threshold test. Select an air resistance that allows a cadence of 95rpm, using the power and cadence tables for guidance. At the end of the test, note the average power and average heart rate. Your FTP value is calculated using 95% of your average power across the 20-minute test.
  2. 60-minute time trial: due to the definition of FTP being the highest power output possible over a 60-minute period, obviously the most definite measure would be to do an hour test! This will also produce a graph which will allow you to determine if the power output was consistent and sustained over the time period.

This doesn’t mean that strength training should be used alone to improve performance; it must be done alongside endurance training in a method known commonly as concurrent training.

Once you had calculated your FTP score, the following table can be used to determine your ‘training zones’:

Zone NumberZone Name% FTP Power (%)% Threshold HR (%)
1Active Recovery<55<68
2Endurance55-7569-83
3Endurance76-8784-94
4Sweet Spot88-9490-99
5Threshold95-1095-105
6VO2 Max106-120>106
7Anaerobic Capacity>120-

Using your FTP to calculate a zone can be done as follows (using Zone 2 – Endurance for an example):

Your FTP score: 250 Watts

250 x 0.55 = 137.5W

250 x 0.75 = 187.5W

Therefore your endurance Watts zone = Between 137.5 and 187.5 Watts