Posted by: Anonymous | 2009/05/11

Heart Rate Zone

Hi Fitness Doc

I recently bought a heart rate monitor and am very confused as to how hard I should be training. I am reasonably fit and trying to get my BMI down from 26 to 22. My body fat is high - about 32% currently (I' m female).

I' ve read Jillian Michaels'  (of the Biggest Loser) book which recommends circuit training &  cardio at 85% for 1hr 5 x per week. I' ve also heard that 60-70% is actually the " fat burning zone"  but exercising in this zone doesn' t even feel like " work"  to me!

Please help - in what zone should I be training? I' m currently cycling/spinning, running and gymming (incl. circuits) for +/- 45 min 6 x per week.

Thank you :)

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Our expert says:
Expert ImageFitnessDoc

Hi there

Common question, and one around which a lot of confusion exists, so you’re not alone. Ever since people noticed that heart rate goes up as intensity goes up, they have used it to gauge exercise intensity. Then, when it was noticed that the fuel that is used also depends on the exercise intensity, it was thought that heart rate monitoring was a good way to train at just the right zone to burn fat. In theory, this is true, but there is more to it than this. What happens is that at low exercise intensities (less than 60% of maximum), the main source of fuel used by the body is fat. As exercise intensity increases above 65 to 70%, progressively more and more of the energy that is produced comes from the carbohydrate stores, meaning that fat contributes a smaller overall percentage of the total energy use.

However, and many people forget this, the overall energy use also increases, so that, even though fat might be contributing less as a percentage of the energy, it is still being used in larger quantities. That means that the total amount of fat being burned per minute might actually be higher at higher intensities, which is what you want. So, many people make the mistake of trying to go at a low intensity, to burn fat, which means that they are probably using more fat than carbohydrate, but the overall energy used is so low that the results are barely noticeable.

SO, basically, the body does not have certain ‘zones’ at which it uses just fat and then just carbohydrates – there is no on-off switch, but a gradual change from fat to carbohydrates, which means that you have to find the exact intensity to burn more fat in total, not more fat as a percentage, if you follow my logic. Also, at slightly higher exercise intensities, the total energy that is being used is greater, which means that the total amount of fat that is being used is also greater – so, to answer the question, I’m more in favour of higher intensity training to burn fat. However, a word of caution, this does not mean going out and training hard all the time. You have to find the right balance. Your goal should be to use the greatest total amounts of fat, and this means that the duration of the training must also be long enough to burn more fat. So, it’s not only the intensity, but also the duration that is vital. That’s why you can’t just go out and train at 90% of maximum – you would tire very quickly, meaning that your total fat and energy use would be relatively low.

Therefore, my advice would be to aim for an intensity between 70 and 80% of maximum, but don’t let a number on a watch tell you what you’re doing. You’re doing 45 minutes of cardio training, and if you can finish that feeling tired, that you’re working hard, but not feeling absolutely wasted and exhausted, then you’re training at the right level. Then what you need to do is take notice of what that value is, and understand that it is YOUR value, and that it is the value that works for you.

The other piece of advice is that you could also exercise at a low intensity (60 to 70%), with short periods of high intensity in between. So, say you are cycling for 45 minutes, every 9 or 10 minutes, you could pick up the intensity for one minute. This type of training is very good for fitness, performance and weight loss.

Good luck

The information provided does not constitute a diagnosis of your condition. You should consult a medical practitioner or other appropriate health care professional for a physical exmanication, diagnosis and formal advice. Health24 and the expert accept no responsibility or liability for any damage or personal harm you may suffer resulting from making use of this content.

Our users say:
Posted by: Anonymous | 2009/05/12

Thanks so much for your detailed answer - the mud is clearer!

Much appreciated

Reply to Anonymous

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