Science at the Summer Olympics

Behind every Olympic victory is an incredible amount of physics, biomechanics, and engineering.  With the Olympic Games in full swing, let’s take a look at the science behind three of its most popular events: running, swimming and gymnastics.

Born to run

Almost eight out of every ten recreational and competitive runners are hurt each year.  This rate of injury has held steady for the last thirty years, even with the invention of running shoes with spongy heel pads, air cushions, springs embedded in the soles, and microchips to direct cushioning adjustment. [1] Sports medicine doctors aren’t surprised by these injuries.  With each footfall, a force equal to more than twice the runner’s body weight hits each leg.  Just imagine repeatedly pounding away at a rock.  Eventually, it will break down.  The same goes for your bones, ligaments, cartilage and muscles when you are pounding away at the pavement.

But humans have adapted to a running lifestyle over millions of years.  Although we are pretty poor sprinters compared to other members of the animal kingdom (think cheetahs), we are exceptional long-distance runners.  We have spring-like arches in the foot, long tendons in the legs, and large gluteus muscles that set us apart from walkers. But perhaps the most important distinction is our ability to sweat, which regulates our body temperature and allows us continue running without fatigue.  In our early days, this ability also allowed us to chase down large prey until they simply became overheated, tired, and keeled over.  How did early humans cope with the impact of running without the aid of microchip-enabled cushioning?

Dr. Daniel Lieberman, professor of human evolutionary biology here at Harvard University, has long been interested in the evolution of the Running Man.  His research group recently looked at how the human foot performs while running with and without shoes. [2] Lieberman and his colleagues compared foot strike patterns of different groups, including American shoe-clad runners and barefoot runners from the Rift Valley Province of Kenya, who are famous for their long-distance running.  They found that barefoot runners tend to land on the front of their foot, while shoe-clad runners land on their heel.  Kinematic analysis showed that landing on the fore-foot generates smaller collision forces and decreases the effective body mass that impacts the ground.  This means less pain, less injury, and the ability to run farther and longer.  It may be a while before we see all Olympians returning to barefoot running, but this may explain why Kenyans, who grow up running barefoot, are such exceptional endurance runners.

Swim like a fish, or frog

Before we evolved into runners, we were swimmers.  But unlike aquatic animals such as frogs or seals, we no longer have webbing between our hands and feet.  This webbing is key, as it creates a paddle that exerts a great force on the surrounding water.  Imagine for a second, that you are nonchalantly running your fingers through the water at a pool.  If you hold your fingers together tightly to form a cup, you exert a large amount of force on the water.  If you spread your fingers apart wide, you exert less force, as the water flows through your fingers rather than around it.   The amount of force exerted is important, because this pulls the swimmer forward and, on the down stroke, upward.  Since air resistance is less than water resistance, the higher the swimmer’s body is above the water line, the faster they go.

However, if you watch competitive swimmers, you will notice that their fingers are spread slightly apart.  Dr. Adrian Bejan, professor of mechanical engineering at Duke University, explains why in a recent paper. [3] The theory presented, and confirmed by computational fluid dynamics simulations, is that spacing the fingers slightly apart generates the maximum propulsive force for a swimmer.  In fact, this optimal spacing (about 0.2 to 0.4 times the diameter of the finger itself) can produce a force in pulling through the water that is 53% greater than a hand held with fingers tightly together.  This increase in force generated occurs because a solid object moving through a fluid creates a boundary layer around it that sticks to and moves with the object.  When the fingers are slightly spread, each individual finger creates its own boundary layer, effectively making an invisible web.  This creates a larger “paddle” which, as mentioned previously, exerts a larger force on the water, allowing for a faster swim.

For more details on how the basic principles of fluid dynamics play a role in becoming a faster swimmer, check out this video produced by the National Science Foundation and NBA Learn.

Soar through the air

Gymnastics is a combination of controlled power, perfect balance and graceful artistry. Science plays a huge part in assisting these athletes to achieve their best performance. Biomechanics applies the laws of mechanics and physics to human performance, a “cause and effect” relationship that determines the motions of living organisms.  Physical principles such as motion, resistance, momentum and friction play an integral part in gymnastics events. Think of when a gymnast attempts to spin in the air.  When they leap from the mat into a twist they use their angular momentum to rotate around a particular axis within their own bodies.  However, for various moves, the gymnast will need to change their rate of rotation, that is, how fast they are going, while in the air.  But how can they change their rate of rotation without pushing off of something?  They do this by changing the distance of their center of mass from the axis of rotation.  As they bring their mass towards the axis, speed is increased and as the mass is extended away from the axis, their speed decreases.  Think of a figure skater spinning on the ice.  As they bring their arms in closer, they spin faster.  You can see this principle at work in all kinds of gymnastics events like swinging on the uneven bars, flips during the floor routines, and even non-gymnastic Olympic events like diving.

Putting it all together

The human body is capable of incredible feats.  We have evolved to run, learned how to maximize our swimming speeds and twist and turn through the air with grace and power.  Behind each Olympian is a team or coaches, scientists and doctors who work diligently to get that extra millisecond faster, those few tenths of a point better, in order to take home gold.  Understanding the science behind the sport and using all the tools of science available to them helps this team reach their very best.

To learn more about the science of running, swimming, and other sports, check out the other videos in the “Science in the Summer Olympics: Engineering in Sports” video series here.

Raluca Ellis is a post-doctoral fellow in the School of Engineering and Applied Sciences at Harvard University.

References

[1] Born to run: a hidden tribe, superathletes, and the greatest race the world has never seen, by Christopher McDougall, Random House Inc, New York, 2009

[2] Foot strike patterns and collision forces in habitually barefoot versus shod runners, a review by Michael Sandler http://www.runbare.com/389/new-study-by-dr-daniel-lieberman-on-barefoot-running-makes-cover-story-in-nature-journal/

[3] Fastest swimmers make webbed hands out of water, by Stephanie Pappas http://www.livescience.com/21309-fastest-swimmers-physics-hands.html