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Body Mechanics

Unique, 3-D modeling techniques have turned some USC athletes into Olympic medalists

July 19, 2004 —

USC's Kaitlin Sandeno will compete in the 400-meter freestyle race during the August Olympic Games in Athens, Greece.
What makes Lenny Krayzelburg's backstroke gold medal material? What sets Kaitlin Sandeno apart from her swim mates in the 800-meter freestyle? What nuances of form did Klete Keller use to close in on Ian Thorpe's world record in the 400-meter freestyle recently?

Skill, a lot of practice, and in some cases, a little help from some high-tech biomedical modeling going on at USC Biomechanics Research Laboratory. The lab, in collaboration with the USC Viterbi School's Departments of Biomedical Engineering and Aerospace and Mechanical Engineering, is running an experimentally based research program to develop state-of-the-art biomechanical modeling techniques for USC athletes who hope to make it to the Olympic Games this year.

"We look at ways to improve a swimmer's flips, dives and strokes, or show sprinters how to spring from the starting line," says Jill McNitt-Gray, associate professor of kinesiology,

Klete Keller, who trained at USC, won the 400-meter freestyle final at the U.S. Olympic trials in Long Beach, CA, and will compete at the Summer Olympics in Athens.
biomedical engineering and biological sciences. "In gymnastics, we'll videotape and model someone's performance to get a sense of how they are generating vertical and angular momentum when they launch a backflip from the balance beam. We can advise them on how to shift their weight just a little or spring up just a little sooner to perfect the performance."

McNitt-Gray specializes in force impact to the lower extremities, an experimental modeling technique in kinesiology that can be applied to a wide range of skilled performers - athletes, musicians and workers at risk of developing repetitive stress injuries - to improve performances without overloading the musculoskeletal system.

Musculoskeletal dynamics

Jill McNitt-Gray
"Integrating experimental and modeling approaches of studying human movement allows us to understand how the nervous system takes advantage of musculoskeletal dynamics and how it distributes load during human movement," she says. "We use engineering mechanics, biology and neuroscience to develop three-dimensional dynamic models of the human body, and then use experimental and simulation results to determine the internal and external forces at work on an athlete's body when they maintain balance, change directions, sprint, flip, or land," says McNitt-Gray, who directs the Biomechanics Research Laboratory on the University Park campus.

The field is called "sports biomechanics," a relatively new field of inquiry spawned by the convergence of knowledge in kinesiology, engineering and human biology. Kinesiology has been around for 35 years, but it's experienced a renaissance with new electronics, video and modeling techniques.

Jill McNitt-Gray, right, works with mechanical engineer Henryk Flashner, who uses motion data to create 3-D musculoskeletal models of athletes.
McNitt-Gray's approach takes several steps. She starts by talking with coaches and athletes to understand the athlete's performance problems. Then she'll attach electrodes to the athlete's body to measure muscle firing patterns and neural control during their performance. With runners, she'll use force plates to measure the amount of push being generated. The data she records during a performance will show her how much force is exerted by different muscle groups and joint movements. She'll combine that model with a video of the performance to come up with some answers.

Krayzelburg's performance

Lenny Krayzelburg’s backstroke — once the centerpiece of USC’s biomechanics research — will take him back to the Olympics in August, despite two shoulder operations and knee surgery.
For instance, an analysis of force measurements and slow-motion video might show her how former Trojan champion Lenny Krayzelburg is moving his shoulders now, after undergoing two shoulder operations. Or they could tell her how Klete Keller is shifting his weight - and how he might adjust it - to increase his speed.

"Simulations will help us identify and evaluate potential solutions that are feasible for each individual athlete," McNitt-Gray says. "Then during training, the coaches will work with the athletes to execute whatever it is - a jump, fall, dive, flip - just a little bit differently, but enough to make a difference."

She works with Henryk Flashner, a Viterbi School professor of aerospace and mechanical engineering, to model the control and dynamics. They concentrate on studying the central nervous system to understand how it is generating force.

Flashner's job is to convert the motion, force and muscle activation data acquired during an athlete's performance into 3-D coordinates and equations of motion. This interdisciplinary approach is based on well-established principles in aerodynamics, he says, and allows the researchers to characterize movements of the spine, joints, arms and legs. The researchers use customized kinetics-processing and dynamics-processing software to crunch the numbers and render 3-D movement simulations. As the simulations are viewed, the researchers can ask a series of "what if" questions about the athlete's movements.

"What ifs are questions like 'what if the athlete modifies the timing of the arm swing? Or what if she strengthens her hip muscles? Or he pushes on the ground in a different direction?'" says McNitt-Gray. "How will these modifications of someone's technique improve the consistency of the athlete's performance under the stress of Olympic competition?"

A musculoskeletal model
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(AVI - 10MB)
A musculoskeletal model of the launch of a backdive shows acceleration forces in different muscle groups, which are color-coded, but closer examination reveals flaws in the diver’s performance at takeoff. Sports kinesiologists and biomechanics will study this motion data and recommend strategies to compensate for weaknesses in the diver’s performance.
U.S. diving team

The researchers' unique modeling has been instrumental in a number of sports training programs, most notably the U.S. diving team. McNitt-Gray takes her lab on the road and works with athletes where they train and compete. She works with divers training at the U.S. Diving Centralized Training Center in Woodlands, Texas, all of whom qualified during trials held in late June 2004 for the U.S. Olympics diving team. She also coaches multi-event athletes at the ARCO Olympic Training Center in Chula Vista, CA.

In addition to Olympics athletes, McNitt-Gray works with some of USC's coaches who want to integrate the latest scientific findings into their athletics training programs. Right now she's working with Mick Haley and Paula Weishoff, who are training the USC women's volleyball team. The work seems to be paying off: USC's women's volleyball team scored two consecutive NCAA championships in 2002 and 2f003.

But she also uses these techniques in a collaborative project with Phil Requejo, a senior research scientist at the Rancho Los Amigos National Rehabilitation Center, to study wheel chair propulsion and balance control of older adults. And the pair collaborates with Rick Naill, a musician and master teacher at the Colburn School of Music, and Anna Pattison and Peggy Tsutsui of the USC Dental School, who are training the next generation of dental hygienists.

Lauren Deutsch, a national level racquetball player and graduate
student in USC's Biomechanics Laboratory, is wired up with electrodesthat will record the electrical activity of her muscles as she worksout.

"If we understand an individual's body mechanics and control mechanisms, we can help them refine their movements and avoid injury to the body," she says. "This goes for dental technicians, athletes, children who play sports, and people who are trying to recover from crippling injuries, such as damage to the spinal cord or losing a limb."

- Diane Ainsworth