For years, it was common knowledge that you had to stay in the target heart rate zone to efficiently burn fat. However, the last few years have seen a rise in the popularity of shorter, intense cardio workouts to burn fat.

Training in your target heart rate zone came about when it was revealed that lower intensity exercise (like walking) burns a greater percentage of fat calories during the activity. More intense work on the other hand burns predominantly carbohydrates. So people would try not to train too hard, because if they did, their body would switch from burning fat, to burning carbohydrates. What most people don’t realise though is that you cannot rely on calories burnt during an activity to lose weight.

Calories burnt during the activity do little to help us lose fat. The critical component of successful fat loss relies on our metabolism and certain hormones flowing through our body. This is why shorter more intense workouts are much more efficient.

Training at a lower intensity burns calories only during the activity. As soon as you stop you will stop burning calories. This is because this form of training hardly raises your metabolism. Also longer, less intense cardio sessions hardly stimulate our body to release hormones which will help our fat loss progress. If done long enough though, you can actually stimulate a hormone that works against us…cortisol. Cortisol is a catabolic hormone which actually eats away at muscle. This is obviously a bad thing!

On the other hand, shorter, more intense cardio workouts release certain hormones, most importantly Growth Hormone. The amazing thing about growth hormone is that it helps us build muscle, and does its best to stop fat from storing on our body. We could eat as much as we want and we won’t put on any fat. (However if you got an absolutely voracious appetite, you might, at worst very slowly put on some fat.) That’s why if we got the hormones flowing in abundance in our body, an occasional pig out day, or binge isn’t going to hurt our progress.

Another great benefit of intense training is that it raises our metabolism substantially, for up to 48-72 hours afterwards. Seeing how it keeps the metabolism elevated for up to 3 days afterwards, imagine what would happen if you did these cardio workouts every other day. Your metabolism would be like a fat destroying furnace!

A good real world example is to compare the difference in physiques between marathon runners and sprinters. Which physique would you prefer? How do you think they train? Marathon runners do hours upon hours of long distance running, whereas sprinters train intensely and explosively. No matter what training we do, our body works by adapting to the stress and making it easier.

So with all the training marathon runners do, cortisol will be running rampant in the body, destroying muscle. This is simply the body adjusting to the workload and making it easier for itself. Too much muscle will only hinder the athlete’s performance (and joints mind you!). That’s why marathon runners have very little muscle.

On the other hand, if we trained like sprinters, with short explosive bursts our body will actually want to keep muscle and burn fat. This is because we need our muscles to better perform the workouts we are subjecting the body to. Also, the body, when exposed to this type of training actually wants to rid the body of its excess fat. This is because the fat on the body is simply hindering its performance. Hence, this is why short, explosive training stimulates hormones like growth hormone which help us build muscle and burn fat.

Well then how should you train? It depends on your goals. Do you want to look like a marathon runner or a sprinter?

If you want to be as thin as a rake, go running for hours on end.

However, if you want that lean, muscular physique much like a sprinters, here are a few suggestions:

30-100m sprints: Set out a distance and sprint all out for the set distance. For recovery, walk back to the starting line. As soon as you get back, sprint again. I wouldn’t do more than 8 total sprints in a workout. For example you could do 6 x 60m sprints.

Intervals: Pick an exercise you like, (running, swimming, cycling, boxing, skipping etc.) and give a near maximum effort (80-100% Max) for 20 seconds, followed by 40 seconds of rest or light exercise (40-60% of max). Repeat 5-6 times. No more than 10 reps is necessary. If you can do 10, focus on going more intense in each interval. I personally like doing these with shuttle runs over a distance of 10-20m.

10 minutes constant max effort: Pick an exercise (running, swimming, cycling) and go as hard as you can for approximately 10 minutes. Try to outdo yourself. You could do 10 minutes every time and try to beat the distance every time you do it OR you could have a set distance and try to beat the time every workout. I personally go down to the oval and time myself over 8 laps of the track.

In finishing, for maximum fat loss, I would recommend doing no more than 4-5 sessions a week. That equals, at most to 60-70 minutes of training time a week. I know it doesn’t sound like much, but if you spend every single one of those minutes going as hard as possible, your metabolism as well as those hormones will melt the fat off your body in no time.

The goal for anyone who wants to lose fat is to achieve maximum fat burning in the shortest time possible. It is very important to choose or create the right training program that is the most effective. There are a lot of discussions and arguments about what is more effective: long duration and low intensity workouts or high intensity workouts. This can be very confusing for people. A personal trainer in one gym suggests low intensity workouts and if you go to a different gym then a personal trainer there may suggest high intensity workouts.

So how much cardio is needed to burn fat?

As it is with so many other things, both sides have some truth in them. The low intensity aerobic exercise proponents say that this method is more effective in burning body fat because if your heart rate gets out of the target heart rate, you stop burning fat for fuel and start using carbohydrates for fuel. That is why so many experts promote this method.

But the problem with this method is that if your exercise is low in intensity, then you just do not burn enough calories. If you don´t burn enough calories then you will not lose fat. It is better to use more intense exercises in your workouts because they burn more calories. High intensity aerobic exercise can use as much as 65% of the body’s energy needs in the form of carbohydrate. Burning calories is more important than what you use for fuel. The harder you work out the more calories you burn.

But high intensity exercises are only effective if you can maintain it long enough to burn more calories then with low intensity. To burn calories effectively your workout has to last from 25-60 minutes. If you do a very high intensity workout but you it only lasts for 15 minutes then it is not effective. The trick is to find the right tempo. The most effective method to burn calories is a relatively high intensity for 30 minutes or so. The only way to find out what is the most effective zone for you, is to find it out yourself. There is no magic number. Trial and error!