The Boxing Day walk is a tradition in many households. Many people like to “walk off” the excesses of the previous day(s). But is low intensity the best option? Most people will have heard the phrase “If you want to lose fat, you should prioritise the forms of exercise that burn mostly fat.” In other words you should train in what is commonly known as the Fat Burning Zone. But what is this and what effects does it have on your results?

What is the Fat Burning Zone

Your body has three main sources of fuel during exercise: carbs, fat and protein. Anytime you exercise at a low-intensity (able to hold a conversation) pace - approximately 60% of your maximum heart rate - about 60% of the calories you burn come from fat. This is because fat takes longer to break down and requires more oxygen so low level activity will prioritise use of fat over carbohydrates.

The Maths

To determine if you are exercising in the fat-burning zone, first calculate as a guide, your maximum heart rate by subtracting your age from 220. Then, multiply that number by 0.6. For example, a 40-year-old will have a maximum heart rate of (220-40) 180 beats per minute (bpm). To achieve the right intensity for this 40 year old to be in the fat-burning zone the heart rate should be at around (180x0.6) 108 bpm.

Is The Fat Burning Zone the Best Way to Burn Fat?

If you are looking for a simple answer to this question - no it is not. Once you increase the intensity of your workout, your body shifts to burning carbohydrates in the form of glucose. Meanwhile, during high-intensity sessions, your body mostly relies on a quick-acting form of carbs known as glycogen. There is no argument that you will burn a greater percentage of calories from fat when you exercise in the “fat-burning zone.” However, you will burn more calories overall if you exercise at a higher intensity and ultimately -depending on the length of your workout - more calories from fat. So how does this theory work in practice?

If you are able to burn 200 calories during a 30-minute session in the “fat burning zone.” then around 120 of those calories (60%) will come from fat. However, if you perform a 30-minute high intensity cardio session, you could burn up to 400 calories, with around 140 (about 35%) of those calories coming from fat. This means that you burned 200 more calories overall and 20 more calories from fat.

In conclusion

It is important to remember that the break-even point of fat-burning for low intensity vs high intensity, depends on factors such as age, sex, level of fitness, mental state, ability but also on length of exercising - usually at about 25 min. Below 25 min you burn more fat at low intensity but it also reduces the benefits of improving factors such muscle strength and general cardiovascular fitness gains. While low-intensity, steady-state cardio may not be the most efficient form of exercise for fat-loss; there are still plenty of good reasons to exercise at a lower intensity. The best form of exercise for weight loss is always going to be the kind you enjoy and will do consistently.

So enjoy that Boxing Day Walk and keep your body burning calories.