May 12, 2026

Adding a power meter to your bike unlocks a world of new insights and perspectives. And while power meters offer a lot of data, one metric stands out: functional threshold power (FTP). From an endurance perspective, FTP represents the most critical aspect of your performance capacity and helps dial in your efforts with customized training zones.

We’ll help you understand what FTP is, how it differs from VO2 max, the science behind it, how you can find yours and how you can improve your FTP.

What is functional threshold power?

FTP is the highest power output, measured in watts, that you can sustain without rapidly fatiguing. This definition comes from Andrew Coggan, Ph.D., an early advocate of power-based training.

Well-trained cyclists can typically maintain FTP-level output for around an hour, though this varies by the individual. Fatigue can accumulate rapidly when your power output exceeds your FTP. Reduce your power output even slightly below your FTP and you may be able to keep going for longer.

It’s worth noting that FTP can be expressed in both absolute and relative terms. In absolute terms, your FTP is the total wattage of your power output. Relative expressions of FTP frame this insight as a power-to-weight ratio (watts per kilo of body weight). The ability to sustain higher power at lower body weights is an important predictor of success in races that involve major climbs.

What’s the difference between FTP and VO2 max?

What about VO2 max? VO2 max and FTP share an important relationship in the pantheon of performance metrics. VO2 max is the number that describes your maximum capacity for aerobic energy production. FTP, on the other hand, captures your ability to sustain higher intensities relative to your maximum aerobic capacity.

For two cyclists with similar VO2 max scores, the rider with the higher FTP may generally have an advantage in competitive settings. And just like VO2 max, FTP can be improved with targeted training methods. 

Physiology and the science behind FTP

The scientific basis for FTP offering useful insight is metabolic in nature. It connects what you do on your bike to what is happening inside your body.

A power meter quantifies performance by measuring energy transfer over time in terms of watts — one joule per second to be precise. Rally™ power meters can determine the force you’re producing right at the pedals, allowing you to compare the force generated between different bikes — regardless of variations in cadence, power and cranks between bikes.

But where does the energy that powers your muscle contractions come from? It’s the result of breaking down adenosine triphosphate (ATP) molecules, a biological resource often called the fuel of life. 

Your body maintains a limited supply of ATP that’s consumed quickly during physical activity. To keep going, your ATP production rate needs to match the energy demand of your performance.

The ATP you use when cycling is mostly produced aerobically, meaning oxygen was available and used in the process. Aerobic creation of ATP is efficient but limited by the ability of your heart, lungs and circulatory system to import oxygen from the atmosphere and transport it to your muscles.

When you need more energy than can be produced with the available oxygen, the ATP needed to make up the difference comes from anaerobic energy pathways — and this can lead to fatigue.

When glucose molecules are broken down for fuel, anaerobic metabolism produces a byproduct called lactate (small amounts of which are always present in your blood supply). The concentration of lactate rises when you exercise and increase the intensity of your performance. Some lactate molecules become fuel for aerobic energy production, while your circulatory system clears other lactate molecules from your working muscles to be remade as glucose in your liver.

Continue to increase the intensity of your performance and eventually the rate of lactate production will eclipse your ability to clear it away, so it accumulates. This can result in reaching your lactate threshold, where you may notice fatigue setting in faster.

How to find your FTP

FTP tests can help estimate the point at which the energy demand results in more lactate production than your circulatory system can clear away. A traditional approach may require taking blood samples during exercise and analyzing them in a laboratory.

Experienced cyclists typically reach the lactate threshold at a higher percentage of VO2 max compared to untrained cyclists. This difference is generally the result of improved aerobic energy production achieved through training.

With Garmin’s auto FTP feature, you don’t have to worry about a 60-minute time trial,…