I’ve had a Polar Heart Rate monitor for about a year now. Cost a packet. Great toy at first, but when it came down to it I really didn’t know how to use it. I’ve just never really understood why it matters. I mean 70% of my max heart rate is pretty slow and easy pace-wise, so why wouldn’t I go above that? Especially when I can work at 85-90% and not even break a sweat! Well recently I’ve started asking at the swish new gym I go to. No-one really seems to know. So I thought I’d do some research myself.
Anyway, to cut a long and very boring story short, I found a website that actually explains it all, but it’s a little ugly so I’m going to copy the details here. Before I do I have to tell you what I’ve done with the info! I started to wear my monitor and decided to keep within the zone according to the article and guess what – after 30 mins I’m drenched! I’m assuming this is a good sign that shows my body is working the way that it should be working. I’m going to stick at this for a while and I’ll report back in and let you know how I go.
So… time for the article…
Many athletes and regular exercisers would love to loose body fat and improve their overall body composition. If we could identify the exercise intensity which evokes the highest rate of fat oxidation, then we could selectively carry out workouts at this intensity and make dramatic improvements to our bodies.
Low intensity sessions to burn off fat
There are two key variables that we need to know:
Fatmax – the exercise intensity at which the highest rate of fat oxidation occurs
Fatmax zone – the range of exercise intensities in which the fat oxidation rates remain within 10% of Fatmax
Researchers from Birmingham University’s Human Performance Laboratory attempted to pinpoint the exercise intensities at which fat metabolism is maximised in a study of 18 male endurance cyclists with a training background of at least three years. Their work found that :
The average value for Fatmax is 74% of max heart rate (MHR)
The Fatmax Zone is between 55 and 72% VO2max (68 and 79% MHR)
Fat oxidation drops to zero above 71% VO2max (84% MHR)
Alternative research has suggested that when you cycle, swim, row or run at a modest intensity of only 50% VO2max (about 69% MHR), fat provides about 50% of the calories you need to keep going for the first hour or so. If you keep going after that, fat becomes even more generous, providing around 70% of the total energy after two hours and 80% or more if your work duration exceeds three hours. If you increase the intensity then the Fat contribution decreases – at 75% VO2max fat provides 33% of the energy.
High Intensity sessions – just as good!
The implication from all this research is that if you wish to burn maximum amounts of fat then you should train in the 68 to 79% MHR window. The reality is that if you train at higher intensities you can burn just as much fat – you cannot be serious – read on
If you cycled along at 50% VO2max, fat would provide about 50%, on average, of the energy you needed to keep going. If you cycle along at 75% VO2max, fat would provide 33% of the required calories. Thus, the slower workout sounds better from the fat breakdown perspective – or does it?
A moderately fit athlete exercising at 50% VO2max generally consumes about 220 calories during a 30 minute workout. If the same athlete works out at 75% VO2max, 330 calories are burned during the same period. Of course, 50% of 220 calories and 33% of 330 calories yield an identical number of calories coming from fat – 110.
Fat provides all your energy
Let us consider the other extreme. If fat alone was meeting all your energy needs, you would not be breaking down carbohydrate during your workouts and as a result your leg muscles would be amply and permanently stocked with glycogen (assuming, of course, that your diet contained a normal carbohydrate content). Each time you ate, the carbohydrate from your meal would be processed and transported to your muscles. Your muscle cells would say, ‘No thanks, I don’t need more carbohydrate, I’m already full.’ The surplus carbohydrate from your meal would then be converted to, you guessed it, fat. Looks like a no win situation – as fast as you burn fat off it is replaced.
Effective way to loose fat
Most exercisers are time constrained to some degree and do not have hours to spend on low intensity sessions. When time is limited, there is little reason to train in your Fatmax Zone. If your overall goal is to get leaner, the bottom line is that calorie burning is the best way to achieve it.
The most effective way to lose body fat is to burn slightly more calories than you take in, and to continue this negative energy balance over an extended period of time.