Some myths never die. And the idea of the ‘fat burning zone’ is arguably one of the most misunderstood fallacies in the fitness industry today!
Let’s begin by defining the theory of the “fat burning zone.” The theory is that by keeping your heart rate in a zone of 50% to 65% of your maximum heart rate (which is low intensity), your body will utilize a higher percentage of your fat stores as a source of energy during the exercise period. This is actually TRUE! But read on to find out why training in the fat burning zone may actually be making you FATTER.
The following fat burning information is VERY important.
During a cardiovascular workout, you will use two sources of energy – 1) adipose tissue (or body fat) and 2) carbohydrates.
1) Low intensity cardio (LIT), or staying within the “fat burning zone”, will produce a greater utilization of fat compared to carbohydrate.
2) Higher intensity cardio (HIT) will produce a greater utilization of carbohydrate compared to fat.
HOWEVER, lets assume that you exercise for 15 minutes using both LIT and HIT…
Your total energy expenditure will be much greater using HIT cardio simply because you’re exerting more effort. Relatively speaking, HIT will use a lower percentage of fat versus carbohydrates, however, in ABSOLUTE terms and because total caloric expenditure has increased, so too has your net fat expenditure. As a result, your net fat utilization during exercise is actually higher during HIT!
Thanks to a study by LaForge and Kosich (1995) it was demonstrated that exercising at a higher intensity for a given time proved to burn more fat than at a lower intensity.
The fact is, you do burn more calories during a long duration low intensity cardio session compared to a short duration high intensity cardio session. But the real advantage of high intensity training is the post workout ‘afterburn.’ Simply put, when you exercise intensely for short periods of time you continue to burn more calories AFTER the workout has finished.
This residual calorie burning effect can last from 24 to 48 hours – and in exercise science it is called E.P.O.C which stands for “Excess Post- exercise Oxygen Consumption.”
What this means is that your metabolism is raised for a much longer period than with a traditional LIT or “fat burning zone” workout.
Something extraordinary happens when you train using high intensity cardio. A study at Laval University in Quebec published in a journal called ‘Metabolism’ back in 1994, showed that high intensity exercise burned off significantly more body fat than steady state endurance exercise. In this case we’re not talking about calories burned during exercise, or whether they came from fat or carbohydrate, we’re talking about actual fat that disappeared from actual bodies.
The research concluded that: Every calorie you burn during high intensity exercise strips off 9 times more body fat than a calorie burned during low intensity cardio!
In other words, to come close to matching the results from a short duration high intensity workout, you’d have to burn off nine times as many calories using low intensity cardio.
Intensity is a function of the duration of your workout. In other words, the longer the workout, the less intense it will be because the body progressively fatigues the longer you exercise. in other words, you can either exercise for a long time OR you can train intensely – but you can’t do both!
But here’s the real problem with long duration, low intensity training and staying and working out in the “fat burning zone.” Training for long periods of time produces higher concentrations of a hormone called cortisol. Cortisol promotes muscle tissue breakdown and a lowered basal metabolic rate (the rate at which you burn calories.) That’s why, over time, long duration low intensity training can actually make you FATTER. (especially if this is the ONLY type of exercise you do.)
What about Fitness? High or low intensity training?
When I first began personal training in the mid 90’s I came across some studies by Izumi Tabata – an exercise scientist in Japan. Dr Tabata and his team compared low intensity exercise (L.I.T.) to high intensity interval training (H.I.I.T.)
In Tabata’s study, one group did a full 60 minutes of moderate-intensity exercise 5 days per week. Group two also trained 5 days a week except that this group performed up to eight 20-second sprints of high-intensity cycling with a 10-second rest (pedaling at a slower rate) in between. This was preceded by a warm up and followed by a warm down.
Total exercise time? Just 4 minutes!
The results were extraordinary. Tabata found that athletes on the high-intensity interval training program increased their fitness levels faster than athletes on a typical endurance training regime – despite the VAST difference in the amount of time each group spent working out. The results are as follows:
Tabata Studies (1996)
LOW 70% VO2max
HIGH 170% VO2max
LOW INTENSITY: 60 minutes
HIGH INTENSITY: 4 mins
Aerobic fitness increase (VO2 max)
LOW INTENSITY: 10%
HIGH INTENSITY: 14%
Anaerobic Capacity INCREASE
LOW INTENSITY: NONE
HIGH INTENSITY: 28%
Participants in the studies who did the 4 minute workouts not only increased their ability to do anaerobic exercise (the type of exercise that features all out efforts like sprints) but also their aerobic capacity. (typically performed at a steady pace with the idea of developing endurance) Whereas group 1 showed no anaerobic fitness increase and a 10% increase in aerobic fitness, group 2 showed a 28% and 14% increase respectively… and all with only 4 minute workouts!
The pnly disadvantage to Tabata’s protocol is that the prescribed intervals are too intense for the majority of fitness enthusiasts. This is why Body Blueprint has developed the Tabata protocol and devised 12 and 20 minute interval workouts.
How Can I Add HIT (Interval Training) to my Workouts?
Choose a cardio machine that allows you to quickly accelerate and decelerate. For example, the elliptical trainer, rowing machine and bicycle are excellent choices.
Next choose 2 speeds that are based on YOUR level of fitness. The first represents 50% of your perceived maximum speed. The second represents 90% of your perceived maximum speed.
Start with a 2 minute warm up at your perceived 50% speed. For minutes 2-4 you would perform intervals of 20 seconds fast (your perceived 90%) and 10 seconds slow (your perceived 50%) When you reach the 4 minute mark you would then take 2 minutes of recovery and return to your original warm up speed of 50%. Depending on your level of fitness this 4 minute cycle can be repeated between 3 and 5 times.
HIT can also be performed as a walk/ jog or jog/ sprint depending on your level of fitness. (It cannot be done on a treadmill as the short intervals do not allow sufficient time to change speeds.)
Is there still a place for traditional low intensity training?
Yes. Especially if you’re starting an exercise program or your sport requires you to do long distance training. However, even with that in mind, I would encourage you to add high intensity interval training to your program as soon as possible – especially if your goal is to increase your fitness, lose body fat efficiently and in the least amount of time possible.
So say goodbye to the “fat burning zone” and welcome to the new era of High Intensity Interval training for MAXIMUM fitness and fat loss!