There is a lot of confusion about the right ‘intensity’ for fat burning. Some claim that low intensity is better, others swear by high intensity, commonly known as HIIT.
Science has the answer.
There are two main fuel sources for your muscles: Fatty acids and Glucose.
Fatty acids are predominantly burned when exercise intensity is low. This is the product of aerobic metabolism.
Glucose is predominantly burned when exercise intensity is high. This is the product of anaerobic metabolism.
Your body doesn’t literally switch from one energy system to the other when you reach a certain intensity. There is an interplay.
But there is a ‘sweet spot’ where your body’s aerobic energy system is stressed to the max. This represents your body’s ‘FATmax’ (maximum fat-burning) and occurs right at the top end of ‘Zone 2’ – somewhere between 65-75% of your maximum heart rate. Max HR is crudely 220- your age.
The majority of benefits of doing cardio are also generated at Zone 2. Elite athletes also spend majority of their training time (80% or so) training in Zone 2
Image Source : University of Colorado Denver | Anschutz Medical Campus
Just check this graph out for a visual representation. 128 BPM on the X-axis represents Zone 2 for the test subject:
This is one of many benefits of low intensity cardio, like cycling, swimming, jogging etc. Cardio has much more benefits than losing just Fat. It will increase your Longevity, Work Capacity and Recovery. Do always work on your Aerobic Fitness.