Train smarter not harder. When you are wanting to improve on your cardiovascular fitness pushing yourself all the time in interval sessions or on runs is not always beneficial. Studies that look at national/international competitive athletes have discovered that their training week typically consists 80% low intensity work and the remaining 20% dominated by high intensity training like interval work. The low intensity work is at an intensity where the body is only producing approximately 2mM blood lactate, also referred to as zone 2 training. To ensure you are training within zone 2, you need to work between 72-82% of your maximum heart rate or at a pace you can sustain a conversation.

Physiological adaptations

One of the key physiological adaptations to low intensity training is capillary densification. Capillaries are small blood vessels that allow for an exchange of gases like oxygen, nutrients and waste products to go between body tissue and the blood. Having an increased number means you will have a greater blood supply to the muscles allowing them to utilise oxygen more effectively and remove unwanted metabolic byproducts to delay fatigue when the body is working at a higher intensity.

Another physiological adaptation is the increase in volume of mitochondria. Mitochondria are the power houses of the body and provide it with energy with the use of oxygen. By increasing the number and size of mitochondria it allows the body to use oxygen more effectively and not have to rely on the anaerobic system so much. All of this creates a good base of fitness and improves VO2 max allowing you to work harder for a longer period of time.

How long should a zone 2 session be?

It is been discovered to gain the desired physiological benefits of zone 2 you need to train within this zone for 1-3 hours but other studies say anywhere from 45mins will be beneficial.

(Seiler, 2010)