What is aerobic threshold?
Aerobic threshold is where the level of lactate in the blood first starts to rise. Each individual’s aerobic fitness level determines the actual heart rate on the aerobic threshold. For example, the aerobic threshold of people with a poor aerobic fitness may be at 60% of their HR max, whereas for trained athletes it may be even at 85% of their HR max.
A higher aerobic threshold allows you to train at higher intensity without lactate building up. When you’re aiming to develop your aerobic threshold, the key is to emphasize low-intensity training. The increased capillaries and the developed fatty acid metabolism improve your body's ability to increase training intensity without increasing the lactate level so much that it can no longer be broken down. In practice this means you can keep going at a higher intensity for a longer time.
What is anaerobic threshold?
Your anaerobic threshold is the highest exercise intensity that you can sustain for a prolonged period without lactate substantially building up in your blood. When you go over your anaerobic threshold, your anaerobic metabolism increases and blood lactate starts to accumulate, which will cause your muscles to stiffen.
Like the aerobic threshold, you develop the anaerobic threshold by pushing it upwards. What this means is that you will be training mainly slightly below the threshold, going over it every once in a while. As your anaerobic threshold goes up, you will be able to train with a higher intensity without the lactate stiffening your muscles.
How to find out your individual thresholds
There are several ways to find out your anaerobic and aerobic thresholds. One of the most popular ways is an exercise test where the intensity level increases step by step, and blood samples are taken from your finger to monitor the changes in the lactate concentration of your blood. This is why aerobic and anaerobic threshold are often referred to as lactate thresholds (lower and upper LT, or LT1 and LT2).
When the level of lactate in your blood goes up, it leads to increased ventilation and CO2 production, so your aerobic and anaerobic threshold can also be determined from ventilation and respiratory gases. In practice, this means taking an exercise test while wearing a mask that measures your oxygen intake and the amount of CO2 in your exhale. These thresholds can also be referred to as ventilatory thresholds (VT1 and VT2).