This week marks the start of the 2019 Tour de France. This year the race covers 2100 miles in 21 days of racing, comprised of team and individual time trials as well as stages through the cities, countryside, and mountains of France, after beginning in Belgium. The Tour de France is interesting to me because it provides an excellent opportunity for a short lesson in sports physiology. This is the topic of my Health & Fitness column in the Aiken Standard this week.
All the riders in the Tour are exceptionally fit since their bodies have adapted to years of dedicated, intense training. Endurance sports like cycling are dependent on the delivery of oxygenated blood to the muscle to produce ATP, the energy needed to sustain exercise. The riders have large, strong hearts, resulting in the ejection of more blood to the muscle. Within the muscle there is an increase in the number of capillaries, the small blood vessels that deliver blood to the muscle, and mitochondria, the part of the cell that produces most of the ATP. Together, these adaptations allow the muscle to produce more ATP without fatigue, allowing the athlete to exercise at a higher intensity for a longer time.
But training isn’t the only reason these athletes can sustain such intense exercise for so long. Proper nutrition, especially what the athletes eat and drink before, during, and after each stage, also plays an important role. Intense endurance exercise like cycling relies on carbohydrates, in particular, muscle glycogen, as a fuel. Muscle glycogen is a storage form of glucose, sugar that the muscle converts into energy. During prolonged exercise that lasts several hours, muscle glycogen levels can be severely depleted.
Eating carbohydrates before exercise can boost muscle glycogen levels, so cyclists eat carbohydrate-rich foods for breakfast before each stage. They also consume carbohydrates in the form of sports drinks (think Gatorade) and energy bars prior to starting. In fact, they start replenishing their muscle glycogen immediately after finishing the previous day’s ride. This usually begins with a recovery beverage, which may contain some protein for more rapid muscle glycogen synthesis, and extends through carbohydrate-rich meals and snacksthat afternoon and evening.
During exercise it is crucial to maintain adequate blood glucose levels, which tend to drop since the muscle is using so much as a fuel. Failure to replenish blood glucose results in what cyclists call “hitting the wall” or “bonking,” which is like your car running out of gas. To prevent this, glucose must be replenished, typically with sports drinks, energy bars, or a sugary mixture called goo.
Prolonged, intense exercise, especially in the heat, results in a high sweat rate which can lead to dehydration. Sweat loss of several liters per hour is not uncommon during cycling, so fluid intake is essential. This means that cyclists spend a lot of time drinking water while they ride. Sports drinks are also commonly used since they contain carbohydrates and electrolytes in addition to water.
Endurance events like cycling, especially multi-stage events like the Tour de France, highlight important concepts of sports physiology. Even though you may never compete at that level, understanding how training can improve your endurance is relevant if you cycle—or run, walk, or swim—for exercise. Knowing how proper nutrition before, during, and after exercise can improve performance can help you make better decision about what to eat. Hopefully, it also gives you a greater appreciation for the science that goes into a performance like the Tour de France.
Dr Parr Says... 