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Rio 2016: The Science of Michael Phelps

Published on August, 10th 2016
By Dr. Greg Wells

This information first appeared in my book Superbodies: Peak Performance Secrets from the World’s Best Athletes.

Michael Phelps is obviously an incredible athlete, but the adaptations of his body may be even more amazing than his performance. His arm span is 2.03 metres wide, longer than average, giving him a greater distance per stroke. This means he has to take fewer strokes than his competitors, which increases his efficiency and saves energy during races. Height and arm length (unlike waist size) are characteristics that are largely determined by genes, but Michael’s commitment to training has had a powerful long-term effect on his body that is not genetic. Most swimmers at the international level will have a lung capacity that can be as much as two times the amount of a normal person’s lungs. No one has published lung-testing data from Michael Phelps yet, but I’d be willing to bet that his lung capacity is beyond limits even for swimmers. So is Michael a product of genetic talent or consistent training over an extended period of time?


Photo (c) copyright Dr. Greg Wells, 2016. All Rights Reserved.

Either we believe that athletes are supremely gifted (in Michael Phelps’s case, with arm length and lung capacity) and therefore outstanding in their sport, or we assume that many thousands of hours of dedicated practice are required to reach these rarefied levels of achievement (like the story of Michael training 365 days in a row when he was 14 years old). It’s the old nature vs. nurture debate, or in the sports context, genetics vs. training.

Exercise changes our bodies via our genetic structures, and training over time can improve not only our blood, heart, lungs and muscles but also our DNA, leading to greater health and performance. Ultimately, Michael Phelps trained very hard, and his coach designed a well-structured program to take advantage of Michael’s genes and develop his physical and mental abilities to the point where he became the best athlete in history.

Achieving world-class performance in any area is not easy. It takes dedication, focus, millions of repetitions and many years of specialized training. Here are some specifics of his performances that are really interesting to dissect.


If you hold your breath, you stop gas exchange in your lungs, causing oxygen levels to drop and carbon dioxide levels to rise. The chemoreceptors notice this change and send signals to the brain, telling you to breathe. You can experience this effect if you try to hold your breath for a minute or so. After a few seconds, you will start to feel the urge to breathe. This feeling is the result of your chemoreceptors sensing rising CO2 levels and sending emergency “breathe harder” signals to your brain. In my PhD research, I studied the effect of training on chemoreception in competitive swimmers and showed that they too can desensitize their peripheral chemorecep- tors. We think that this desensitization benefits swimmers by training away the urge to breathe. This allows them to hold longer strokes without rushing to the next breath, and to make more efficient turns because they can stay below the surface of the water longer after pushing off the wall. The incredible distances Michael Phelps swims underwater on his turns went a long way toward helping him win all those gold medals.


Lactic acid contributes to the fatigue process. If you’ve recently heard that this statement isn’t true—and that lactic acid is in fact a fuel for muscle—please read on. Lactic acid is a fuel for muscle. But it does play a role in fatigue. Let’s consider a sprint event—the 100-metre butterfly (100-metre fly) in swimming. It’s a great event to analyze because the butterfly is a difficult stroke for most people. It’s also the event that Michael Phelps won by 0.01 seconds in the 2008 Olympics, on his way to winning eight gold medals. The 100-metre fly takes very little time—about 50 seconds to complete if you’re swimming at the Olympics—and the energy output is very high. Muscles are stimulated to contract with great force as quickly as possible, while the brain adjusts the motor patterns to ensure the athlete sustains the required technique.

Since the muscle power and energy consumption are high, the brain recruits all fibre types (I, IIa and IIb) to help move the athlete through the water. Within the muscle itself, both the fast- twitch oxidative and glycolytic fibres break down stored sugars for energy into a form of sugar called glycogen. Glycogen is broken down into glucose, and then, through a series of steps, into a substance called pyruvate. This process of breaking down sugars in the muscle is called glycolysis, which is why the fast-twitch fibre energy system is termed the anaerobic glycolytic system. Glycolysis does not require oxygen to function, and produces energy in the form of ATP very quickly. This ATP is used to fuel muscle contraction during the butterfly stroke. But there’s a problem, and anyone who has tried to swim 100 metres of butterfly—even Michael Phelps—has experienced it. You’ve probably experienced it, too, when you run up stairs or sprint to catch a bus.

Because of the high muscle-energy demand, glucose is broken down faster than it can be processed in the mitochondria. This causes the accumulation of a substance called lactic acid. It’s this acid that causes a burning sensation in our muscles and makes it hard to keep working at the same intensity. Lactic acid breaks apart into a lactate molecule and a hydrogen ion. The hy- drogen ion—not the lactate—increases acidity and disrupts the metabolism of the muscle cell. Nerve fibres sense the acid buildup in the muscles and let the brain know there are metabolic problems in them. The lactate is stored until the intensity of the exercise decreases. It is then converted back into pyruvate and processed in the mitochondria, or reconverted back into glucose or glycogen for storage (this process is called gluconeogenesis). So lactic acid is both a fuel (the lactate part) and a fatigue agent (the acid part).

For an athlete to finish the 100-metre swim, one of two things must happen. First, the athlete must slow down and work aerobically to process fuels through the mitochondria. Second, as shown by Michael Phelps, the athlete is so well trained that he is able to use his aerobic system at such a high rate that not much lactic acid is accumulated—or, if it does accumulate, the athlete is able to maintain speed and fight through the mental and physical pain of this buildup to the end of the race.

There are more races to go at Rio 2016 so I hope this helps you enjoy the coverage even more!

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