Article: Brenda Entwisle from FAIRLADY

Most of us remember with dread the compulsory cross-country running forced on us at school. It may well have been responsible for turning a vast majority off exercise for life.

There were some who put their heads down and slogged their way to the end, red-faced, puffed out and epitomising the cross part of cross-country. And there were those enviable lithe few for whom it was just a walk in the park. They seemed to have an innate capacity to go the distance, and then some.

But what gave the enduro-bunnies their vastly superior staying power? "Stamina," says Johannesburg cardiologist Joe Tyrrell. Stamina is essentially the ability to keep on going, and cardiovascular capability is at the heart of the matter.

Our muscles need oxygen to produce the energy that fuels physical activity. Oxygen is carried around the body via the haemoglobin in our blood cells. And it is our heart that pumps the blood through our bodies.

The stronger our hearts beat, the further the blood is pumped around the body, and the more oxygen our muscles receive to work their magic.

There is no trick to a stronger heart. The heart is a muscle, and barring a transplant, the only way to make it stronger is to exercise. So the good news is that if your Go! Go! Go! got up and went, you can get it back again.

It all comes down to a biological principle grandly called the general adaptation syndrome (GAS). It is a vaguely similar concept to the supply-and-demand curve that I never got the hang of in economics class.

If you demand more of your body, it will adapt to the greater demands and supply you with what you need. If we stress ourselves short of the point of breakdown and allow a recovery period, our bodies undergo an adaptation and can then tolerate a greater stress.

If you are a couch potato and you go for a walk around the block before collapsing back onto the couch, tomorrow you will be able to do a block-and-a-half before seeking the solace of the couch.

Take that principle to the nth degree, and the couch potato will one day have the stamina to run the Comrades Marathon.

What is stamina
Stamina is the ability to keep working the whole body over prolonged periods of time without tiring -­ an impossible feat if we're constantly gasping for breath.

The ability of our lungs to extract oxygen from the air we breathe is a vital component of stamina. The more we exercise, the more efficient our lungs become, and the more oxygen is available to our bodies.

So, with more oxygen extracted by our lungs and more oxygen-infused blood pumped further around the body by our fit hearts, we are able to comfortably perform for longer and longer. And yes, you can tell your partner that this will have a carry-over effect to pump up his performance in bed.

Bedspring aerobics aside, by engaging in more exercise, we are also building up our muscles. Exercise expands the network of capillary blood vessels that feed the muscles with oxygen, meaning that they receive more oxygen via the bloodstream.

The increased oxygen supply enhances the muscles' ability to endure for longer. Heart, lungs and muscles: It's a real multiplier effect, with stamina at the end of the equation.

Are we born equal?
Are some people genetically built to go the extra mile? If you fall into the laggard leg in long-distance events, you will appreciate affirmation of what you've always suspected: Genetic heritage definitely does play a role in stamina.

"People are born different. And although training will increase your stamina to a certain point, you will never overcome your genetic legacy," confirms Dr Tyrrell.

"People have different genetic predispositions to energy economy. Some are just more efficient in their use of energy, and the more economical their energy consumption, the better stamina they have," agrees Prof Geoff Rogers of the Department of Physiology at the University of the Witwatersrand.

Despite coming from a Third World economy with less advanced training facilities, athletes from Kenya dominate the endurance events in international athletics. What's more, this phenomenal raw talent comes predominately from one tribe in the Kenyan highlands who are genetically built to go the distance.

Just as we cannot change our genetic heritage, our gender is pretty immutable.

Do men hold the winning baton in the race for stamina?
They do hold a key advantage over women in the stamina stakes -­ men essentially dope their blood with oxygen. By virtue of greater levels of testosterone, men have a higher oxygen-carrying capacity in the blood.

Each litre of male blood can carry about 11% more oxygen than a similar quantity of female blood. So, on a physical level, men have a greater ability to keep their muscles energised with oxygen.

"Men are just bigger in general, and that means a bigger heart, more blood and a higher haemoglobin concentration, resulting in the potential for better stamina," says Jimmy Clark, a biokineticist at the Institute for Sport Research at the University of Pretoria.

Despite this physical advantage, the longer the distance, the closer the performance of male and female athletes.

Scientists at Wits researched a sample group of women and men who finished a standard marathon in approximately the same time.

They found despite the women's lower aerobic capacity to derive energy from oxygen, they were still achieving the same time as the men in a standard marathon. When this same sample ran the Comrades Marathon, the women were about half an hour faster than the men. Indeed, women are even beginning to win ultra-distance races internationally.

The jury is still out on which factors contribute to this phenomenon, but one theory is that it is women's greater ability to cope with frustration. And any woman who have children can attest to that.

Our parents have a lot to answer for -­ especially when it comes to the genes we inherited for body type.

We're all a mix of three main kinds of body types: