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Biomechanics International Biomechanics International
by Nathan Hurst
Issue 12
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It was the last home game of the season, and the Wisconsin Badgers had just been scored on and were now losing to the Iowa Hawkeyes. The football announcer's voice crackled across the airwaves preceding the Hawkeyes' ensuing kickoff, "Now kicking into the wind, we'll see how strong Kyle Schlicher's leg really is," he said. But he was only partly right.

How far an athlete can kick a football, or throw a shot put, or how well he or she can perform almost any event depends on much more than muscle strength. Form, angle, physiology, and biomechanics are hidden factors that play important roles in dictating how well an athlete can do his job, and even how well a person can walk or balance.

One of the areas these factors have been used and studied is the therapy of stroke victims, who often have trouble walking. It now seems likely that their problems are directly related to the brain's ability to control muscle movement.

"For much of athletics, what's more important is control, how that force generated by the muscle is regulated," said Kreg Gruben, professor of biomedical engineering at the University of Wisconsin-Madison. Biologists have explored how nerves connect muscles to the brain, and how they cause muscles to activate, but they don't yet understand how the nervous system controls those actions.

"That's why these factors are hidden," he went on. "We don't know how the control works." The actual mechanics are solvable using the laws of physics, but Gruben's work attempts to go beyond combining physics and biology, and reaching into neurology as a way to understand movement of the human body.

The problem was that he was in uncharted territory. "What do we know?" he asked. "I looked, and what I had to do was back up and back up and back up." He started with a simple action, walking, and had to dissect it completely.

"To understand how people walk, you want to understand first how people generate force," he said. In the past, that meant observing the action of walking and measuring everything possible about it. That was especially difficult because walking is very complicated, with many different muscle actions that a persons brain must coordinate simultaneously. So Gruben took a different approach.

He isolated a simpler task involved in walking. A seated subject would push with his or her foot on a pedal that measured both the force exerted, and the direction pushed. "What we're getting is their preferred direction of force," he said. In most individuals, the direction they push forms a straight line from their foot through their center of balance, which is the point in their body about which their weight is evenly distributed.

Stroke victims often have difficulty walking, even years after they have recovered. Many exhibit peculiar gait, and have health problems associated with it. Gruben looked at the direction of force in stroke victims, and noticed an important difference. It didn't go through their center of balance.

To see why this is important, imagine being seated in a car on a Ferris wheel. The center of balance is the hinge it is mounted on. If an attendant pushes on the car directly towards the hinge, it won't move. However, if he shifts and pushes a little more upwards or downwards, the car will begin to swing.

It is the same with walking. If your body isn't pushing off the ground in line with the center of balance, the natural tendency will be to rotate, and your head will end up where your feet were.

To keep from going head over heels, stroke victims compensate by using their muscles and joints in different ways, and often require physical therapy to correct it. Unfortunately, the gait they are trying to correct is only a symptom, and other compensations must be made unless the ultimate cause is fixed. That's where muscular control comes in.

When the brain sends a signal to a muscle, it can be telling the muscle one of a few different things. The signal can mean shorten, stiffen, generate force, or simply 'become active'. But which is it? This could apply to athletics, Gruben said, but perhaps not yet.
"I think we need to get those questions answered before we ask why one person can perform better than others," he said.

In spite of all that remains unknown, a coach or an athlete working on improving athletic ability is not operating completely in the dark. Gruben let on that there is some truth in the methods that have been used for many years.

One man who has been using those methods is Rick Witt, coach of the University of Wisconsin-Stevens Point men's track and field and cross country teams, and 1996 National Collegiate Athletic Association Division III Cross Country Coach of the Year. He records video of runners and analyzes it to help them become more efficient.

"What we try to do is to look at any of the things the individuals do that are not taking advantage of physics," he said. "My job is to look at these people and find the mistakes they are making so we can remedy them and make sure they are maximizing how efficient they can be." That is biomechanics. Biomechanics means applying the laws of physics to biological systems.

The form Witt's runners use is not universal. For example, the form of a sprinter differs significantly from that of a distance runner. Sprinters lift their heels much higher, shortening the length of the lever that is their leg, and leading to quicker turnover and faster top speed, explained Witt.

A distance runner requires less force, but over a longer time. Witt pointed out that while not as important as certain other physical aspects of an athlete, biomechanics can make as much as a 10 to 15 percent difference in performance, or three minutes over a 30-minute cross country race. He compared a runner to the engine of a car. "Having an efficient engine is not going to make up for having less horsepower, but if you have similar engines and one is tuned up and one is not, which one is going to win?"

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