Cycling is an endurance sport supported by your body’s ability to burn carbohydrates and fats in your muscles and generate energy. There are two primary energy systems, Aerobic and Anaerobic. One of those is sustainable for hours and the other can only be sustained for minutes before the build up of waste products in your muscles forces you to stop. Understanding where YOUR threshold is between these systems and being able to work with it and improve it to increase you power and endurance is the primary goal of training.
The aerobic systems burns fats and carbohydrates efficiently, and the by-products are energy, water and CO2. You can use this system for hours with only gradual build up of fatigue, but there is a limit on how much power you can generate in a given period of time. The anaerobic system burns only carbohydrates, and it does so very quickly to generate a sharp increase is energy, but it does it inefficiently. It generates lactic acid as a by-product, which builds up in your muscles causing a burning sensation and rapid fatigue, so you can only use it for a very limited period before your body shuts down.
The Functional Threshold is the point at which you body moves from using the aerobic system as the primary source of energy and the anaerobic system takes over. This happens when the demands of your muscles exceed what your aerobic system can supply, such as when you’re sprinting or climbing hard. This threshold can be measured by your heart rate (Functional Threshold Heart Rate – FTHR) or power (Functional Threshold Power – FTP).
So, why is know the thresholds so important? Firstly, you can use these to pace your efforts to go as fast as possible without causing extreme fatigue. For example, if you’re climbing a long hill and you know your FTHR is 150 beats/minute, you can limit your effort to keep your heart rate at that level. In that way you go as fast as possible without generating excess lactic acid. Secondly, if you’re racing, you can decide when you’re going to go “into the red zone” and learn how long you need to drop back down below threshold to recover before making another surge. Most importantly, by understanding where your threshold is, we can develop training programs to both improve your endurance and raise your threshold, so you generate more power before you reach the threshold and Go Further, Faster.