The physical macro environment. Some form of physical activity has been a requirement for survival and day-to-day Irving for most of human history. Famous Swedish exercise physiologist Per-Olaf Aastrand has pointed out that if the whole of human history over 460 million years was regarded as a race of 460 kilometres, only the last 10mm would have been covered by a 100-year-old man living today. The period during which machinery has taken away the need for physical effort has really only been the last 40-50 years, or 2-3mm on the 460km journey of the human race!

As the need for physical activity in day-to-day life has decreased, such activity has become increasingly institutionalised through the development of the modem fitness industry, however, the use of a gym for 30 minutes a couple of times a week probably doesn’t compensate for the decrease in spontaneous physical activity during the rest of the week. The idea of a fitness centre also has limited appeal to many people, particularly those who are excessively fat, and figures show that only 1-2 per cent of the population actually use these facilities on a regular basis.

In schools, the presence or absence of physical education (PE) classes and facilities for physical activity through play can influence the early development of obesity. Where physical education was once compulsory in Australia, this is now often left to the discretion of individual schools. Trials with a compulsory daily PE program in South Australian primary schools in the 1980s showed that this not only decreased body fat and improved measures of health in young children but also aided academic performance. The growth in childhood obesity is now leading to a re-evaluation of the need for PE by education authorities in some parts of the world.

Finally, the increasing urbanisation of the population has, in many cases, led to a decreased opportunity for increased energy expenditure. Where there are facilities such as walking paths, bike tracks, or other recreational facilities, but no street lighting, there are often concerns about personal safety, particularly for women and children. Positive changes to the macro environment to increase daily energy expenditure will need to include provision at the national and local Government level for safe recreational facilities. Indeed, possibly the best way to motivate individuals to increase activity is to present them with easy exercise choices.

If the fitness industry is to participate in fat loss there will also need to be a significant change in its image. New facilities are currently being developed in some countries that de-emphasise the fitness and ‘body beautiful’ aspects of exercise that are de-motivational for so many people, but allow opportunities for safe, regular, low intensity, long duration activities such as treadmill walking, cycling and stair climbing, accompanied by electronic entertainment such as videos, TVs, and stereos.

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The process of lipolysis, or breakdown of fats. There are a range of receptors on the membrane, or surface of the fat cell, which respond in a number of different ways to a range of messenger chemicals, or hormones. These are a bit like locks and keys which open the cell up for a cascade of events which then result in the enzyme HSL being activated to break down TG into FFA plus glycerol for release into the bloodstream. This metabolic cascade, or amplification of chemical reactions, is common in nature and enables a much larger response to a small stimulus to occur. Enzymes, or catalysts, also take part in these reactions enabling them to be sped up to the rate necessary for a biological response.

There are over 30 different receptors, or ‘locks’ which have been identified to date on the fat cell membrane, and many more likely to be discovered. The ? (beta) receptors are important receptors which facilitate lipolysis. The hormones which lock into the 8 receptors are adrenalin and noradrenalin (catecholamines), both of which are involved in responses to stress. Factors affecting catecholamine production (and therefore potentially lipolysis), include exercise, cold, stress, caffeine and some other stimulant drugs, such as the amphetamines (which have, in the past, been the basis for some weight control drugs).

The lypolytic hormones ‘unlock’ a cell receptor, and the signal is then amplified through proteins inside the cell which in turn generate a substance called cyclic AMP (cAMP) which continues a cascade of events ending in the activation of the enzyme hormone sensitive lipase (HSL). This is the final step in the enzymatic attack on stored triglycerides which are hydrolysed (broken down) into FFA and glycerol. The circulating FFAs released may then be re-esterified back into the fat cell, or released to the circulation or taken up by other tissues to produce energy. The final combustion of FFAs in cells to produce energy is known as fat oxidation, and is the process by which stored body fat is ultimately used.

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