Remember Mark Spitz, U.S. Olympian with the aquatic "Midas Touch"? At the 1972 summer games in Munich, Spitz captured gold in the individual 100-meter and 200-meter freestyle, 100-meter and 200-meter butterfly, and as part of three medley relay teams.

Boston University had its own Spitz-like Water Dog. University Hall of Famer Scott Riewald ('92) competed during his Terrier years in much the same way as Spitz, entering up to seven events at a meet (most competitive swimmers enter no more than three) and churning up win after win with a variety of strokes. His numerous University and America East individual and relay records remain unbroken.

But now, as director of biomechanics at USA Swimming, located at the U.S. Olympic Training Center in Colorado Springs, Riewald says, "I don't know if you'll see another Mark Spitz, who excelled in as many events as he did. Swimming is much more specialized. There is a more concerted effort to identify a swimmer's abilities earlier on and to focus on a stroke that emphasizes these abilities." Ironically, Riewald the generalist is now part of that effort. USA Swimming, formed in 1978 after the passage of the Amateur Sports Act, is responsible for the conduct and administration of swimming in the United States and, in this capacity, formulates rules, conducts national championships, selects athletes to represent the U.S. in international competition, and disseminates safety and sports medicine information.

Riewald draws on his training as an engineer -- and his firsthand experience -- to study the biomechanics of swim stroke strengthening. His career path is not exactly surprising: "Scott totally dedicated himself to the sport of swimming from day one," says BU's head swimming and diving coach, Reagh "Doc" Wetmore. "He'd work on his weakest strokes the most, and he did everything he could to improve." As a sports scientist, Riewald suggests improvements to swimmers from youth to masters-level based on a biomechanical analysis of swim stroke patterns made from each swimmer's performance in a state-of-the-art swimming treadmill called the flume (see "The Phenomenal Flume").

"Most swimmers and even their coaches don't understand how things move through the water," says Riewald, who has always been fascinated by the human body and how it moves. After earning his undergraduate degree in biomedical engineering from the College of Engineering (Riewald achieved a 3.86 GPA while making and breaking numerous BU and North Atlantic Conference swimming records), he earned a master's and Ph.D. in biomedical engineering at Northwestern, studying sensory motor performance in children with cerebral palsy.

At USA Swimming, Riewald is both researcher and educator; he designs lectures and workshops to teach the basics of biomechanics, physiology, and sports psychology to swimming coaches. "There are a lot of things that a coach can't see that are just as important as getting a swimmer to swim fast," says Riewald, "so it's important for me to get that information to the coaches in a format that is easily understood." Swimming coaches generally believe that performance improves with training, but Riewald shows coaches and swimmers how significant improvements can be made through technique changes as well. "I don't think I put all of this together when I was at college," he says. "If I could take what I know now back to the BU pool, I would be an even better swimmer."

Let's Get Physics-al

Why do some people swim with the ease of a porpoise while others thrash about like fish out of water? In truth, there are no "natural-born" swimmers; both graceful and graceless swimming depend upon hydrodynamics, or the physics of fluids. What distinguishes a good swimmer from a great one is not just practice in the pool, but applying what you learned in school. Knowing basic principles of engineering and physics -- understanding what happens when an object (a swimmer, in this case) meets resistance from the water, for example, and how to minimize this resistance -- can make you a better swimmer.

• Archimedes' principle. A body in water is buoyed up by a force equal to the weight of the water displaced. When the weight of the water you displace is greater than your weight, you float, because the force of buoyancy is greater than the force of gravity.

• Specific gravity. People float at very different heights in the water -- why? The ratio of the weight of a body to the weight of the water it displaces is its specific gravity. Pure water has a specific gravity of 1.0; this is the standard against which other objects are compared. A body with a specific gravity less than 1.0 floats; one with a specific gravity greater than 1.0 sinks. People with lots of muscle, heavy bone structure, and little body fat do not float as easily as those with more body fat and less muscle. Females generally are better floaters than men (the average female has 21 to 24 percent body fat, while the average male has 15 to 20 percent); so, too, are very young children (who have more fat weight and less muscle) and older people

• Drag, or resistance. Movement in the water is affected by three types of water resistance: form drag, wave drag, and frictional drag.

- Form drag is resistance related to the object's shape and

profile in the water. A tight, narrow shape experiences less form drag than a broad shape; the narrow shape has to push less water aside. A streamlined position in the water (legs together, arms tight above head or to the sides) reduces form drag.

- Wave drag is resistance caused by water turbulence. The faster the swimmer, the more wave drag. Smooth, even strokes with minimal up-and-down and side-to-side movement help reduce wave drag. Movement under water, such as during turns, also reduces wave drag.

- Frictional drag is resistance caused by the surface texture of the body as it moves through the water. That's why competitive swimmers wear swimming caps and smooth, snug swimsuits; some even shave their body hair.

• Bernoulli's theorum of laminar flow. As a fluid moves around an object (a swimmer), its molecules either speed up or slow down and stay parallel to the molecules on the other side of the object. Molecules that slow down because of drag create pressure against the object, while those that speed up pull the object toward them with a force called lift. Lift and drag combine to affect the movement of a swimmer through water.

• Conservation of momentum. Circular stroke patterns are more efficient than linear movements because back-and-forth movements use force to stop moving in one direction and then to resume movement in another direction. Keeping ankles stiff while doing the flutter kick results in a less powerful kick because of the back-and-forth, linear motion. With relaxed ankles, the more "rounded" path increases efficiency. n

The Phenomenal Flume

The flume, or swimming treadmill, is located at the International Center for Aquatic Research at the U.S. Olympic Training Center. A simulated current keeps the swimmer in place during stroking while the hypobaric chamber adjusts the simulated altitude so a swimmer can work out at sea level (thereby adjusting the 6,035-foot altitude of Colorado Springs) or in higher-altitude conditions (such as in Mexico City, which is approximately 8,000 feet above sea level).

Because no two swimmers perform the same stroke in exactly the same way, cameras at each of the flume's underwater viewing windows (on each side and at the bottom) record a swimmer's stroke and body positioning. The tape is digitized, a computerized biomechanical analysis of stroke patterns is made, and a propulsion chart is generated so stroke patterns can be analyzed.

The flume weighs nearly 1 million pounds, is 25 meters long, 4 stories high, and holds 50,000 gallons of water. Its 265-horsepower pump moves the water at speeds up to 3.0 meters per second, which is equal to a 33-second, 100-meter freestyle swim. Since the world record for this event is 48.2 seconds (held by Russian Aleksandr Popov), the flume will be able to test swimmers for years to come.