It is widely assumed that exercise is a key part of controlling one’s weight. However, there are many people who find that exercise alone has very little impact on their weight while others seem able to exercise and lose weight easily. What is going on? Well, people all respond slightly differently to exercise due to age, sex and their genetic inheritance. However, despite any difficulty in losing weight that you may have inherited, there are different forms of exercise that will definitely be able to help you lose weight. The different forms of exercise all have different effects on weight loss. Below I look at:
Easy/medium intensity cardiovascular exercise – aerobic.
Hard, high intensity cardiovascular exercise – anaerobic.
Weight training and other resistance exercise.
1 Aerobic exercise
What is aerobic exercise? Aerobic exercise is exercise which most people can sustain for hours if properly conditioned. Heart rates are typically 55-85% of the maximum heart rate. You breathe in oxygen through your lungs at a rate which generally allows you to talk. Your heart then pumps blood containing the oxygen to your muscle fibres. As your muscle fibres contract to produce movement, they use up oxygen. The harder and faster you go, the more oxygen that you need, and as a consequence you breathe faster. As you increase your effort your muscle fibres burn up more sugars and fats to produce the energy required to make them contract. The result? You burn calories faster.
What is fat burning? Fat burning is a form of aerobic exercise that became popular in the nineties. It is basically lower intensity aerobic exercise. Heart rates are at typically 55-65% of the maximum heart rate. Unfortunately it is not the best way to remove excess fat. You actually burn more fat as you increase the effort. Although the fat burning zone burns a greater proportion of fat compared to sugar than high effort zones, the high effort zones burn both more fat and more sugar. The amount of sugar burnt increases faster than the amount of fats as you up the effort, and so you could say you enter a sugar burning zone as you go harder. However, along with the sugar you will also be burning more fat. There are many studies that have looked at the weight loss effects of aerobic exercise. Most show a small positive benefit, but one that is far less effective than modifying dietary intake. These studies have been mostly done on sedentary or obese people and involve amounts of exercise typically of between 2-4 hours per week. The truth is that if you are not intending to do more than 2-4 hours of aerobic exercise per week, then you are unlikely to lose much weight as a result, unless you also significantly modify your diet. However, that is not to say you shouldn’t do it. Most studies also show that physical and psychological health both benefit significantly from this small amount of exercise when compared to doing nothing. Larger amounts of more intensive aerobic exercise are generally more effective at achieving weight loss. The effects of larger amounts of exercise on people vary. Some are responders and others non-responders. Non-responders are thought to be people who reduce their levels of everyday activity when undertaking an exercise program, in order to compensate. In other words if you are going to treat yourself with extra food or slump in front of the TV after introducing a new exercise routine then it may well not have any effect on your weight. I have many clients who are responders, who eat more healthily when exercising a lot and who treat hip dip themselves when they are having a break from their hard exercise routines. Needless to say these clients are prone to developing a small paunch when taking it easy, but find it easy to lose the weight once they start up their exercise routines once again.
2 High intensity – anaerobic exercise
Anaerobic threshold is defined as the point during a graded exercise test at which lactate in the blood begins to accumulate faster than it can be got rid of. A fit athlete can maintain an effort at the anaerobic threshold for about 1 hour as long as the blood lactate does not continue to rise. If the intensity of exercise continues to increase from this point, as it would in a graded exercise test, then acidification occurs. This is due to the accumulation of hydrogen ions formed when the lactic acid produced in muscle is converted to lactate. The acidification soon causes a severe muscle fatigue and the intensity of exercise can no longer be maintained.
What is anaerobic exercise?
Your muscle fibres, and most other cells in your body have two main routes of making energy. The first is aerobic respiration in which sugar or fat is burnt with oxygen in the mitochondria to produce the energy. Think of mitochondria as power stations. The second is anaerobic respiration, in which sugar is turned into lactic acid without a need for oxygen to produce energy. This happens in the sarcoplasm of the muscle cells. Anaerobic exercise occurs when you run low on oxygen. As you exercise harder your muscle fibres try to get more oxygen into the mitochondria to burn your fuel faster. As you pass through your anaerobic threshold (see panel to the left), your body is not providing enough oxygen for your mitochondria to produce all the energy you need. Your muscle then increasingly relies on the anaerobic respiration in the sarcoplasm. So at this point the mitochondrial power stations are working at close to full capacity and as a result you are breathing pretty hard. Anaerobic respiration is interesting in that it uses up sugar 15 times faster than the mitochondria. How could this affect weight loss? Well this form of respiration is now burning calories 15 times faster than the mitochondrial one. The fact is that as you push harder beyond the anaerobic threshold you make increasing use of anaerobic respiration and so burn calories at exponentially increasing rates. You reach a point at which your breathing is at a maximum. This is called the VO2max. A fit athlete may be able to maintain this rate of breathing for a maximum of 10 minutes. Your mitochondria are now working at full capacity and your anaerobic respiration in the sarcoplasm is working towards maximum. The anaerobic metabolism is building up lactic acid, which results in increasing acidosis in the muscles the longer and harder you go on. The fatigue becomes unbearable and you soon slow down.