By Ollie McCarthy

If you are looking to use fat as the predominant fuel source of your workout you need to gain a certain level of fitness first. 

The greatest fat utilisation will be when you are working aerobically (when your body is using oxygen to break down fat.) Which means you have to keep your heart rate (at a certain heart rate you will effectively swap from using fat to using carbohydrates as fuel) at a lower level for prolonged periods of time for this to be effective.

The problem with this is that so few of us spend any time working our aerobic system that it’s weak. So whenever we do any form of cardio or conditioning at any sort of intensity, our heart rate usually sky rockets above the level we need to work at to use fat as a fuel source. 

So what are our options?

1-  We don’t focus on heart rate and look to get fitter through an initial period of hard work. This will mean that although we are working at a higher heart rate than will be effective, in the long run our fitness will improve. This in turn will allow us to work at lower intensities for longer periods further on down the line.

2- We work at the lower heart rate and over time we will be able to do more intense workout at a lower heart rate as we will get fitter. This can be a slightly more difficult as it challenges our ego. For some people working at this intensity may just comprise of them walking fast or run/walking. 

This would probably be my preferred way of getting fitter as there are multiple physiological and psychological benefits of working aerobically. 


To burn fat as a fuel source you need to get fitter, which in turn means you need to spend time on developing your fitness.

It is important to point out that overall weight loss and body composition change will come as a result of a calorie deficit. Using the above methods should be used in conjunction with this if that is what you are looking to achieve.

About the author

Ollie is a running coach and personal trainer working out of Halo Gym. His background is more strength based having played Rugby League and competed in amateur strongman. More recently he has turned to more endurance based sports and regularly runs having completed 6 ultramarathons and enjoys getting out on his road bike. His philosophy on training is building “all round fitness” so you can expect him to draw from a combination of barbells, kettlebells, boydweight, core and mobility work while also making sure cardiovascular fitness is covered. He believes the benefits of training suprass that of the physical and is passionate about helping his clients become more physically and mentally resilient with a focus on health being a priority.