This is Part 7 in our ongoing series exploring the dimensions of health. Parts 5 and 6 have been concerned with the physical dimension and we will now complete that dimension with the elements of exercise, rest and sleep.

The tenth item on our list of the determinants of physical health (from Part 5) was concurrent health in the other dimensions. This covers all of the rest of this series, so I won't attempt to elaborate on it within the physical dimension. Hopefully at or towards the end of our series we will be able to expand on the holistic nature of all of the dimensions.

So the first determinant for today is regular strenuous exercise. The completely effortless existence where no physical labor is performed simply isn't compatible with good health. Imagine that, all those tools that reduce our need for effort aren't actually so good after all.

Physical exercise is needed for the proper operation of most body systems. The complete absence of exercise results in rapid loss of physical functions, quickly and particularly noticeable in muscle performance. Most people have been confined to bed for three or four days at some stage with the flu. On getting up and about again it usually comes as a bit of  a shock to discover how weak one feels, and just how much muscle tone has been lost in such a brief period.

Equally, when people have an arm or leg immobilized in a cast or splint for some weeks, they notice just how much muscles waste when they aren't used. This loss of muscle tone and muscle bulk represents a real decline in physical wellbeing. Happily, it can be readily overcome in most cases with return to exercise effort to get the muscles back to work.

The exercise actually needs to be reasonably strenuous. Our bones depend on work effort to maintain their strength. Demineralization of bone is a very real threat to health and unfortunately is a very common problem. Inadequate nutrition combined with insufficient strenuous exercise results in an unavoidable insideous loss that, while it may take years or decades to show, seriously undermines health.

Of course, regular strenuous exercise also tones our heart and vascular system, assists the digestive system and has a beneficial effect on the endocrine and nervous systems which seems to enhance our sense of wellbeing. The absence of this last benefit is commonly associated with depression and hence regular strenuous exercise frequently lifts affect, or state of mood.

We can't exercise all the time though. We also need to rest. There is a cyclical or rhythmical pattern to life and the exercise - rest cycle is part of it. The body needs time to repair any damage sustained, to renew tissues that are constantly in need of replacement and to attend to other housekeeping or maintenance functions. Exercise and rest work together and both are important.

Inadequate rest can result in an increase in wear-and-tear injuries. It can also result in inadequate tissue cleansing of the toxins accumulated by normal metabolism.

Of course the ultimate form of rest is something quite special; it is sleep. We do need sleep. We need it regularly and ideally that means a shut down period every day. We also need to get quality sleep, though individuals do vary considerably in their particlualr requirements.

During sleep we seem to do a full reset. It confers many of the benefits a personal computer derives from a reboot! In the case of humans, we do seem to process or reset our mental function nad we do something quite similar physically.

Sleep has differing depths and stages through which we need to pass to derive the most benefits for health and wellbeing. While people are fairly tolerant of sleep disturbances they definitely should be taken seriously if they persist.

Most people know that insufficient quality sleep can reduce their performance mentally and physically. Generally people talk about the psychological benefits of sleep and problems associated with its lack. But significant physical changes take place during sleep, including important hormonal activity.

So strenuous physical exercise, adequate rest and regular quality sleep are all important determinants of physical health. We'll leave this here for now and move onto physical fitness in Part 8.