J.B.S. Haldane, one of the most eccentric and brilliant biologists of the twentieth century described four stages in the acceptance of a new theory.
1. This is worthless nonsense.
2. This is an interesting, but perverse, point of view.
3. This is true, but quite unimportant.
4. I always said so.
The public remains in stage one or two with regard to some essential truths in health and fitness.
Let's start with one of the most unfortunate misunderstandings in health and fitness history, "FAT BURNING ZONES". The most common reason people exercise is to lose fat. And in the vast majority of cases, they fail. But it's not their fault. The public was told that longer duration low-intensity exercise, like a jog on a treadmill or a steady session on a stationary bike provides the heart rate that is optimal for burning fat.
For a definitive review of how aerobic exercise fails as a weight loss strategy see Thorogood et al. American Journal of Medicine 2011 Aug;124(8):747-55
It is true that in this "fat burning" heart rate zone proportionally more fat than carbohydrate is used. But there is much less total fat burnt with these exercises than more demanding routines, such as interval training. But we should have known something didn't sound right.
Here's a quick quiz?
Who has a higher body fat percentage, the marathoner or the sprinter?
If you said this has to be a trick question and I'll go with the counterintuitive response, you were correct! Why is the sprinter, whose training runs total less distance, less time, and consume less calories, leaner? Because he does resistance/weight training. That's right. It's exactly the opposite of what we were led to believe. Metabolic or interval resistance training, which the pros have been doing since the 1950's, is the most time-efficient way to burn fat. It gives the biggest bang for the buck and you see results faster than with any other intervention.
The reason these more intense forms of exercise burn more fat is because they induce a metabolic disturbance that requires lots of energy to recover from. This is a key point. It is not how many calories or how much fat you burn during the exercise. It is what happens after. All the pathways that are stimulated in order to address the "insult" of excessive demand during the exercise are sometimes called the "afterburn". This includes a host of reactions such as EPOC (Excess Post-Exercise Oxygen Consumption) and increases in resting metabolic rate. Let's face it, if you work out an hour a day (which is heroic) that leaves 23 non-exercise hours per day. If your routine only changed your physiology during that hour, it could not have much impact on anything.
I know this sounds like an advertisement, but it gets even better.
The "fat burning zone" concept is actually a symptom of a much larger misconception, the endurance/cardio training - strength/resistance training dichotomy. Most of the world, from doctor to fitness professional to health conscious layman believe that these are mutually exclusive domains. This has also proven to be false. And that's good news.
Traditionally, exercise has been classified as either strength or endurance. Strength training consisting of short-duration, intense muscular work that results in hypertrophy, vs. endurance training which is characterized by prolonged, low to moderate intensity work that results in increased oxidative or aerobic capacity. The scientific community believed that these two forms of exercise triggered different pathways that could not be engaged simultaneously. However, recent research has found considerable overlap in these two pathways.
For example, high intensity interval training (which is really just using resistance training with supersets or circuits to elevate heart rate and not allowing for sufficient recovery between sets) produces similar metabolic and performance adaptations to endurance training. No one thought it was possible to improve aerobic performance this way. In fact, HIIT appears to be better than endurance-type training for muscle buffering capacity (getting better at eliminating lactic acid).
I'll leave you with a study that beautifully illustrates what we've been speaking about today. Bryner et al. in Effects of resistance vs. aerobic training combined with an 800 calorie liquid diet on lean body mass and resting metabolic rate in Journal of the American College of Nutrition, 1999 April;18(2):115-21.
( I'm sure you noticed the 800 calorie diet! The authors were interested in looking at the effect of different types of exercise on subjects on a very low-calorie diet (VLCD). One of the problems with VLCDs is their tendency to cause muscle loss and lower resting metabolic rate, two things that make it even more difficult to loose weight. )
So, there were two groups, one did aerobic exercise, the other resistance training. The aerobic group exercised for four hours per week and the resistance group did 2-4 sets of 8-15 repetitions for 10 exercises, three times per week.
Both groups lost weight. But the resistance training subjects did not lose muscle, lost much more fat and experienced an increase in their resting metabolic rate compared to the aerobic group. (The aerobic group's metabolic rate decreased.) The most stunning result, however was the VO2max increased equally in the two groups!
So if you want to improve aerobic performance, get stronger, and lose fat, intensify and shorten your workout.
For once, less is more.