Low and high intensity aerobic training

Low intensity aerobic exercise, eg walking or swimming, will burn up body fat, so once you are lean, you can keep your body fat levels down by low intensity aerobic exercise every second day. You can use the time you have left over to step up to the next level of fitness, where you train your body to absorb a higher level of physical stress.

These are the kinds of stresses you feel when you get involved in sports, take up running, use weights or resistance training, or attend intermediate level aerobics classes. This form of exercise is called high intensity aerobic training (HIA).

High intensity aerobic training will not significantly decrease your body fat levels but it will give you the ability to exercise continuously at higher levels, with minimum fatigue. High intensity aerobic training will also help you develop more muscle shape, or muscle definition. This kind of training needs to be done two or three times a week and makes a useful addition to low level aerobic training.

Disadvantages of high intensity training

The main problem with high intensity aerobic training is that you start to use body sugars (glycogen) as the main body fuel. At higher exercise intensities, your body finds it easier to get sugars (rather than fat) to the working muscles, and to break them down for energy supply once they are there. Using sugars as a fuel is not necessarily bad, but your body stores of sugars are limited. Once body sugar levels get low you may start to get that tired, drained feeling, and feel like you have to slow down. You may also start to get dizzy.

Your brain relies on sugars as a fuel, and won't tolerate low blood sugar levels. Dizziness is a message to your body to stop the activity, lie down, and let your brain soak up some more sugars. Learn to recognise and avoid this lethargic feeling. Slow down your activity before you get to the point of fatigue.

Taking your pulse

The best way of working out how hard you should be exercising for high intensity aerobic training is to take your pulse. For high intensity aerobic exercise, your heart rate should be between:

• 25-30 beats every 10 seconds if you are younger than 20
• 23-28 beats every 10 seconds if you are younger than 30
• 21-26 beats every 10 seconds if you are younger than 40
• 19-24 beats every 10 seconds if you are younger than 50
• 17-22 beats every 10 seconds if you are younger than 60
• 15-20 beats every 10 seconds if you are younger than 70.

What is interval training?

The kind of training you do for high intensity aerobic conditioning is called interval training. This means that you alternate an interval of high intensity work with an interval of low intensity work. You push your heart rate up towards the top of the training range in the high intensity intervals and let it come down to the bottom of the range in the low intensity intervals. This is the way most intermediate level aerobic classes are designed.

You do a track of hard work, then a track of easier exercises. If you are walking or running, warm up first, then go slightly faster for three to five minutes, slow down for three to five minutes, and repeat this six to 10 minute 'interval' a couple of times before going into recovery.

In a gym circuit, your instructor should design the exercise stations so there is a regular 'rest stop', such as an exercise bike, at every third to fifth station.

Recognising overtraining

Make sure you have at least 12 weeks of regular low level aerobic training before starting high intensity aerobic training. Don't overdo high intensity training, or you will be training your body to become fatigued, not fit. Learn to recognise the symptoms of over training, such as:

• muscle fatigue
• muscle 'burn'
• dizziness
• feeling queasy
• having a dry mouth
• getting a stitch
• seeing spots in front of your eyes.

What you can do if you overtrain

Slow down your activity to a walking pace, but don't stop. Once you feel better, rejoin the activity or start your recovery phase. A good recipe for general fitness is low intensity aerobic training three times per week, and higher intensity aerobic training twice per week. This will keep you lean and give you the fitness everyone needs to cope with the stresses that come your way everyday.

Original material supplied by Monty Dortkamp, Chief Executive Officer, Fitness Australia and Managing Director of the Australian Institute of Recreation. Edited by everybody, March 2005.