Athletes and Fat – A Little More

Almost all cyclists and runners know that excess body fat can hinder performance. Although it’s immediately apparent that there are substantial differences in physical characteristics between cycling sprinters and climbers, elite runners and 100 meter sprinters, They come in a variety of shapes and sizes, and there are perhaps too many exceptions to make broad generalizations. Generally speaking though, sprinters have powerfully developed musculature of the upper body and of the legs, while climbing specialists and long distance runners have low body mass, with smaller muscles and extremely low body fat levels.

The one outstanding characteristic of very successful competitors in all almost all endurance sports is a low body fat content. The body fat stores account for about 15-18% of total body weight in normal young men, and in young women the figure is about 25-30%. ‘Normal’, of course, is changing along with the size of the Mexi Fries at Toco Bell, and those ranges should be qualified as being normal for healthy people. Most of this fat is not necessary for energy supply and is simply extra weight that has to be carried throughout the race.

Fat Guy Heading Up A Climb

Our fat stores are important and the fat cells play many key roles. As well as acting as a reserve of energy that can be called upon at times of need, fat is important in the structure of tissues, in hormone metabolism, and in providing a cushion that protects other tissues.

An excess of body fat, however, serves no useful function for the endurance athlete. It can help the sumo wrestlers, and perhaps may not even be a disadvantage for the shot putter, but not the cyclist or runner. Extra fat adds to the weight that has to be carried, and thus increases the energy cost of running. Even in an event as long as the marathon, the total amount of fat that is needed for energy supply does not exceed about 200g for the average runner.

The article that I read makes reference to A very lean male 60kg runner with 5% body fat, it says that he will generally have 3kg of fat; a typical elite 55kg female runner with 15% body fat will have more than 8kg of body fat. Non-elite runners will commonly have at least twice this amount, and many runners further down the field will be carrying 20kg or more of fat.

It is probably not sensible for men to let their body fat levels go below about 5% and for women below about 10-15%. There’s good evidence that the immune system is impaired when body fat stores are too low, check out the previous post about body fat.

Fat typically contributes about half of the total energy cost of a long bike (this is very approximate, and will depend on speed, fitness, diet and other factors). At low speeds in ideal conditions, the total energy demand is low and most of the energy supply is met by oxidation of fat, with only a small contribution from carbohydrate in the form of muscle glycogen and blood glucose (which is continuously being replaced by glucose released from the liver). So for anyone who is looking to lose weight this would be the place to start… go slow!

Greg's Twig Legs

As speed increases, the energy cost increases more or less in a straight line, but the relative contribution from fat begins to decrease, with muscle glycogen becoming the most important fuel. The problem with cycling or running slowly to reduce body fat levels is that it takes a long time, because the rate of energy expenditure is too low. Run too fast, and you burn only carbohydrate, leaving the fat stores more or less untouched.

Body fat and performance

In a study of a group of runners with very different levels of training status and athletic ability, scientists observed a significant relationship between body fat levels and the best time that these runners could achieve over a distance of 2 miles. Although these results indicated that leaner individuals seem to perform better in races at this distance, some complicating factors have to be taken into account.

The relationship between body fat and race time may at least in part be explained by an association between the amount of training carried out and the body composition. It would hardly be surprising if those who trained hardest ran fastest, and it would also not surprise most runners to learn that those who train hardest also have the lowest fat levels. Indeed, body fat content does tend to decrease as the volume of training increases.

The runners covering the greatest distance in training had the lowest body fat levels. They also ate more food than those who did less running. There are, of course, some people who do not fit the line as well as others, but there are many factors that explain this variability. We would expect the people who eat more to be fatter, but no! The subjects who did most running had the lowest levels of body fat, even though they did eat more. Thus, we can separate food intake from body fatness if we add exercise to the equation.

Fat levels in elite athletes

Skin fold thickness estimates of body composition in 114 male runners at the 1968 US Olympic Trial race gave an average fat content of 7.5% of body weight. Since then, similar measurements have been made on various groups of runners, and the findings are fairly consistent.

Catherine At The Beer Mile

The low body fat content of female distance runners is particularly striking; values of less than 10-15% are commonly reported among elite performers, but are seldom seen in healthy women outside sport. The occasional exceptions to the generalisation that a low body fat content is a pre-requisite for success are most likely to occur in women’s ultra-distance running, and some recent world record holders at ultra-distances have been reported to have a high (in excess of 30%) body fat content. However, this probably reflects the under-developed state of women’s long distance running; as more women take part, the level of performance can be expected to rise rapidly, and the elite performers are likely to conform to the model of their male counterparts and of successful women competitors at shorter distances.

Although there’s an intimate link between body fat levels and running performance, it’s important to remember that reducing fat levels will not automatically guarantee success and may even be counter-productive. If you reduce fat by a combination of training and restricting diet, you are walking a fine tightrope. While a reduction in body fat may well boost running performance, cut down food intake too drastically and not only will training quality suffer, but the risk of illness and injury also increases dramatically.

The majority of this information comse from pponline.co.uk – a great resrouce

Tags: Biking, body fat, Cycling, Distance, elite, fast, fat, losing weight, prefromance, Running, sprinting, Training