A non-athlete will be aware of being to be able to do more, more easily and with less tiredness.

Fitness means the effective delivery of glucose and oxygen to the tissues, efficient metabolism and removal of waste products and more energy turned into activity and less wasted in heat.

Biochemically it is perhaps the PO2 at the level of the mitochondrion and the ability to uncouple ATP and to release energy more swiftly and efficiently.

There may be accompanying biochemical or physiological parametyers so that fitness will be associated with a Haemoglonin level of 120-150 mgs./litre, increased insulin sensitivity, a normal lipid profile…. or a blood sugar and blood lipid level within the low normal range.