Dr. Christine Thorburn
As racers navigate sharp curves , race down hills and make steep climbs mile after mile, one wonders how they find the energy after they have cycled for so long already. The answer involves more than just well developed muscles. Top cyclists use training techniques that actually change their bodies’ cells.
“Human bodies generate energy to move muscles by breaking chemical bonds that hold molecules together,” explains Dr. Christine Thorburn, a rheumatologist at the Palo Alto Medical Foundation (PAMF) who competed in women’s cycling in both the 2004 and 2008 Olympics. “As part of this process, lactic acid is created. It used to be thought that this acid was just waste and the cause of muscle fatigue and soreness. However, research has shown that the body’s cells can actually take excess lactic acid and convert that to even more energy. Training improves this ability.”
As a medical resident at Stanford University during her first Olympics and a practicing physician during her second Olympics, Dr. Thorburn understood the importance of what was happening inside her cells to the outcome of her races.
“Part of what makes Lance Armstrong such a good cyclist is that he can process lactic acid into additional energy very effectively,” Dr. Thorburn says. “When someone is not very well trained – as I am now that I am retired – lactic acid will build up during strenuous cycling and one’s leg muscles will begin to burn. Once this happens, an untrained person has to stop and rest. They cannot recover. Keep going and one may start to feel dizzy and stop thinking clearly. However, a well trained cyclist can go above his or her lactic acid threshold for several minutes at a time, recover and then do it again two or three more times during a race.”
Cyclists have to go above their lactic acid threshold when “attacking” in a race to gain an advantage over the rest of the group of riders drafting one another. At the end of an “attack,” the body has to process the excess lactic that built up during the sustained burst of energy. Some lactic acid is processed by the liver, but much of it is taken up by a portion of individual body cells called the mitochondria. The mitochondria are the cells’ engines and create additional energy as they break down and get rid of the lactic acid.
Through interval training – which involves short bursts of high intensity exercise interspersed with low intensity exercise that allows the body to recover – cyclists can increase the number of mitochondria inside their cells. With more mitochondria, the cells become even better at processing lactic acid.
In training for the Olympics, Dr. Thorburn and other U.S. cycling team members used sophisticated tools that let them scientifically measure everything from the force they applied to the bike pedals to the lactic acid levels in their blood. They then used these measures in training to maximize their ability to process lactic acid during races.
“Training is all about knowing when you are going above your lactic acid threshold and knowing how long you can sustain that effort,” Dr. Thorburn says. “In training, you can use tools to help identify when you are in that zone, but in a race you have to go by what you are feeling.”
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