Why do athletes spend most of their training developing their aerobic capacity for short events that require a large anaerobic component to win?

The physical distress an athlete feels after an all-out effort in a short race is due to the extensive utilization of the anaerobic system. No one denies that the anaerobic system is key to success in these events. But why do athletes in these short events spend most of their time developing their aerobic capacity when it is anaerobic capacity that will provide the top energy to win? It turns out that the aerobic system is also very important for short events, but not primarily because of the energy it provides. It is a source of energy but it also has an extremely important housekeeping function. It cleans up many of the metabolites produced by the anaerobic system.

A quick review of the properties of the aerobic and anaerobic systems would be useful at this point. The aerobic system produces most of our energy for life and it has no negative side effects. The outputs are harmless. One is water which we dispose of in sweat or other ways, and the other is carbon dioxide which we exhale. The one negative of the aerobic system for athletic activity is that it is produces heat. It also produces energy relatively slow. See aerobic metabolism in our triathlon section.

The anaerobic system provides energy and it produces it very quickly. There are two anaerobic systems and each has major negatives. The creatine system provides energy very quickly but only for about 8-12 seconds and then it is exhausted. The glycolytic system provides energy not quite as fast as the creatine system but much faster than the aerobic system. It has enough fuel to last for several minutes but produces metabolites (mainly hydrogen ions) that prevent muscle contraction when present in large amounts. If these metabolites accumulate to a large extent, the muscles must slow down or stop.

Now this is where the aerobic system is most important. As we said the aerobic system provides energy. But its main function in a short event is to utilize the metabolites from the anaerobic system, using them as fuel. This allows for use of the anaerobic system at a higher level and for a longer time. The anaerobic system is what will win short races. So the bigger the aerobic capacity, the more the speed systems can be used for shorter races. One way of looking at this is that the aerobic system is the gatekeeper that decides how much of the anaerobic system can be used.

A good explanation of this was provided to us by Xeno Muller, Olympic and World Champion (single rowing sculls). He likens the aerobic system to a vacuum sucking up all the bad metabolites so that the anaerobic system can be used longer and harder. He emphasized the necessity to utilize the anaerobic system at high levels in order to do well. It is what wins races but also leaves the athlete extremely wiped out.

Building this aerobic capacity is a long process. For a rower, swimmer, runner, cyclist, skier etc. to reach maximum aerobic capacity it may take years of slowly building up mitochondrial density. Adjusting the anaerobic capacity is a much quicker process and can be done over a short period during a training season. We will see in the next question that for a longer distance, anaerobic capacity has completely different implications.

One interesting implication of this is that the lactate curve will move to the left as the athlete gets more fit. The reason is that to achieve the speed necessary to do well in short events, the glycolytic system which produces lactate is used at high levels. This moves the curve to the left.