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 dont 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, you can actually stimulate a hormone that works against you, 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.
Another great benefit of intense training is that it raises our metabolism substantially for up to 48-72 hours afterwards. Seeing how it could keep 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!
So, if we train 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, short, explosive training stimulates hormones like growth hormone which help us build muscle and burn fat.
Well then how should you train? If you want to be "lean and mean", 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 wouldnt 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.
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.
In finishing, for maximum fat loss, I would recommend doing no more than 4-5 sessions a week. That equals, at most 60-70 minutes of training time a week. I know it doesnt 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.
And you will still have time to do that intense strength workout which will also help raise your metabolism!