Weight and Cycling Performance

Weight is a crucial factor in determining cycling performance, particularly in professional cycling. In the world of Grand Tours such as the Tour de France, Giro d'Italia, and Vuelta d'Espana, the lightweight cyclists dominate the General Classification (GC). Gone are the days when larger, stronger cyclists from Denmark or Spain would win the Tour de France. However, having a low weight also comes with its downsides. This article explores the advantages and disadvantages of being a cyclist with a low weight.

Weight on Flat Terrain

A professional cyclist's body is composed of approximately 10% fat, 15% bone, and 50% muscle mass. This means that a cyclist weighing 70 kilos would have 7 kilos of fat. On flat terrain, weight is not a significant factor as the primary obstacle is air resistance. A kilo more or less has a minimal impact on the frontal surface area. For instance, a cyclist riding alone at a speed of 42 km/h in a windless environment would have to overcome approximately 87% air resistance, 10% rolling resistance, and 3% loss in transmission. This requires a total power output of 350 Watts. Weight does affect rolling resistance, but a mere two-kilo difference only saves about 0.5 Watts. Even in a sport that obsesses over marginal gains, this is considered negligible. It's worth noting that body mass plays a vital role in acceleration abilities, such as during sprints, but that is beyond the scope of this article.

Weight's Impact in the Mountains

In mountainous terrain, weight becomes a significant factor. At a 9% gradient, our 70-kilo cyclist would ride at 16 km/h while exerting the same 350 Watts. At this relatively low speed, aerodynamic resistance accounts for only 5% of the overall resistance, while the resistance caused by the gradient (gravity!) amounts to a staggering 88% of the total resistance to overcome. With two kilos less body weight, the cyclist would need 10 Watts less power to maintain the same speed. Conversely, with the same power output, a cyclist weighing 2 kilos less would go 0.5 km/h faster.

Based on this theoretical explanation, it is evident that trainers, teams, and riders strive for the lowest possible weight. GC contenders in Grand Tours aim for a fat percentage between 5% and 8%. However, this low percentage is not sustainable year-round but is specifically sought after as the start of one of the Grand Tours approaches.

Achieving Low Fat Percentages

To achieve such low fat percentages, a strict diet tailored to the training load is essential. Weight loss requires training with a negative energy balance, meaning the intake of calories must be lower than the expenditure. On an average training day, a professional cyclist burns around 3000 kilocalories. Additionally, fuel is needed for the body's normal metabolism, requiring a total consumption of approximately 4200 kilocalories to prevent deficiencies. Striking a balance that allows optimal recovery from training efforts while creating a calorie deficit is a challenging puzzle. Recent research indicates that the resting base metabolism of frequent athletes is lower than that of less active individuals. This may be due to the preference for reduced activity following intense exertion. Therefore, cyclists are advised to rest as much as possible when not training.

The Role of Ketones

When aiming to lose two kilos of weight, it becomes crucial to create a caloric deficit that prompts the body to utilize stored fat tissue for energy. This metabolic state, called ketosis, involves the conversion of stored fat into ketones, which serve as an additional natural energy source for cells. Fat tissue conversion into ketones occurs when there is an insufficient supply of carbohydrates nearby for energy conversion. Hence, encouraging the body to use stored fat as energy requires a state of near-starvation. Training with a low carbohydrate supply, known as sober training, is one method to achieve this.

However, this approach is not without risks. The main danger lies in the fact that energy systems in the body are never fully separated but rather intertwined. For example, the body always burns a small amount of protein, but at low intensity or with adequate carbohydrate availability, protein utilization remains minimal. Proteins are essential for muscle building. When carbohydrates are nearly depleted, and the body starts burning stored fat tissue, protein utilization for energy increases. This not only leads to weight loss but also causes a loss of strength due to inadequate muscle tissue regeneration. In essence, the body begins to consume itself. A telltale sign of this process is an unpleasant ammonia taste in the mouth. The challenge in training physiology today is to achieve weight loss through negative energy balance without sacrificing power.

The Problem of Extremely Low Fat Percentages

Extremely low fat percentages have their drawbacks. Firstly, adhering to an extremely strict training and nutrition regime over an extended period of time can be mentally challenging. This explains the weight fluctuations often observed among the favorites in Grand