FIT for LIFE Knowledge Base Nutrition

Sport and Body Weight

Whether an endurance athlete can perform well is also a question of physique and weight. How much more power does a low body weight bring?

How light is light enough?

Anyone who goes hiking in the mountains with a heavy backpack will feel the handicap of an additional weight within a very short time. And although numerous factors ultimately determine athletic performance, weight is a key factor, especially in endurance sports.

The explanation behind this is first and foremost purely physical: with fewer kilos, the weight-to-power ratio improves and with each step less weight has to be lifted and absorbed. If the force of gravity has an even stronger influence, the more you perform with less weight. Whether marathon runners, Tour de France winners or mountain runners: the fastest athletes in these categories are all “pencils” and not “erasers”, such as the sprinters.

Take the marathon for example: successful runners like Haile Gebrselassie (164cm/54kg) or even Viktor Röthlin (172cm/60kg) are lightweight, and mountain and ski tour runners like Kilian Jornet (171cm/58kg) are often below the 60kg barrier. In amateur sports, weight also plays a role in performance: training experts assume that over the marathon distance, every kilo too much on the ribs adds about two minutes to the final time. Or to put it another way: If you are overweight, every kilo of fat you lose in preparation for a marathon gives you two minutes more time to finish. It is important, however, that the weight reduction really does involve the loss of fat mass and not muscle mass, so that weight loss could not be achieved by a radical diet within a short period of time, but by a long-term change in behavior. And just as important is where the line between ideal and overweight is set.

Healthy BMI

One measure of this ratio is the so-called body mass index, or BMI for short. It makes it possible to measure the relationship between height and weight of different people. It is calculated using the formula: BMI = mass divided by body height squared. Example: A runner 1.80 m tall with a body weight of 75 kg has a BMI of 23.1.

In the standardized assessment, a BMI below 18.5 is considered underweight, a BMI between 18.5 and 25 is normal weight, and a BMI above 25 is overweight. When comparing the fastest runners, the BMI varies between 18 and 21 in terms of peak performance in running, surprisingly regardless of whether the runner runs over 800 m or a marathon.

However, the BMI as an estimation parameter has a serious disadvantage: not only the ratio of height to weight, but above all the ratio of weight to muscle mass is decisive for the personal maximum performance in a discipline such as running. To make an exact prediction of the personal performance capacity solely in relation to the BMI is therefore of little use. After all, it can be predicted that the body weight ratio or BMI normally shifts in a positive direction over the years of training: “heavy” muscle mass is built up through training, but this is overcompensated by an even greater reduction in fatty tissue.

This results in a BMI of typically about 20 for fast to very fast athletes after years of training. Apart from sprinters, this value is common for top runners regardless of the running distance selected. Sprinters have a significantly higher average BMI because of the large muscle mass required for improved speed. The BMI of the five fastest sprinters of all time is just under 22, which is around 10% higher than the average value of the five best runners of all time over 800 m, 5000 m and over the marathon distance.

Balance is crucial

For already well-trained and lightweight athletes, it is not the BMI but the right balance that is crucial. Somewhere there is an individual weight limit that must not be undercut without losing too much mass. It is often difficult to judge where this limit lies, especially since performance often increases significantly with less weight. Until it suddenly tips over and additional weight loss causes more damage than it saves time. In competitive sports, this can quickly tip over into anorexia in individual disciplines (long-distance running, cross-country skiing or even ski jumping) with dramatic consequences.

Conclusion: In order to be able to run as fast as possible for as long as possible, many conditions must be right. The body weight is only one of many components. In addition to the physical characteristics (height, weight, proportions), optimized metabolic processes (oxygen uptake and transport capacity), psychological conditions (e.g. attitude, motivation, will), motor components (condition and coordination) and their mutual interaction are also responsible for a peak time. Accordingly, the focus should be versatile and should be placed on all components and not only on a low body weight.

This Blog Article was made available to us by Fit for Life. Fit for Life is the Swiss magazine for fitness, running and endurance sports. Would you like to read such articles regularly? Then Click here.