What exactly is a biomechanic? The Biomechanics page at Vassar College's site gives a good description: "A biomechanic (or biomechanist) applies physical principles to understand how an organism functions, how it is constructed, and how its performance and evolutionary potential might be limited. In this way, a biomechanic combines techniques and concepts from the fields of comparative physiology, functional morphology, evolutionary biology, physics, biochemistry, and mechanical engineering." In other words, a biomechanic studies any aspect of the mechanical side of biology.

The field of biomechanics covers a wide range of topics, anything from the strength of a cytoplasmic structure to the buoyancy of a blue whale. A good deal of biomechanical work examines locomotion, how animals get around - flying, jumping, running, swimming, walking, wiggling, or whatever. Being walkers more than runners or swimmers (and certainly more than fliers), humans tend to look very carefully at gait, which is the way a terrestrial animal moves. Horses give us a good look at different gaits, such as walking and trotting. Humans can use several gaits, too, from walking to skipping to running.

To take a tour of animal gaits, turn to the Gait Analysis Page. It provides many links to pages about gait. Wherever one goes, one should make sure to stop by Clinical Gait Analysis. Among other things, this site posts a Case of the Week, which is a description and a movie of a patient with a walking problem. This site also gives visitors a wealth of data on the patient, such as measurements of various flexions and extensions. For visitors who want to test their knowledge of gait, this site offers Teach-in pages, which lead to a series of experiments along with data and questions. The Gait and Clinical Movement Analysis Society will help one keep up with most of the general activities in this field. This site publishes an electronic newsletter and maintains links to a variety of laboratories and information about meetings.

Many animals get around without taking many, if any, steps at all. For a broad introduction to the biomechanics of getting around in water, return to Vassar's Biomechanics page and wade around in its section on swimming. This area includes descriptions of the muscles involved in swimming and how they make a fish's body undulate. Visitors can also study photographs and descriptions of many aquatic animals, including a dolphin, a marlin, a skate, and others.

Many insects also swim, especially during early developmental stages, and it appears that swimming somehow spawned flight. A primitive insect called the stonefly performs a behavior that looks like something between swimming and flying. In some cases, the stonefly holds up its wings like little sails and skims across the water like a windsurfer. On the other hand, this insect can also flap its wings to use them like a propellers to power its skimming. Jim Marden, an expert on insect flight in general, studies the stonefly and others. He posted QuickTime movies on his Web site of their surface-skimming. Fortunately, he posted short segments that download quickly. Despite the short length of the movies, they show the behavior quite well. Beginners who still need to "get their wings" - folks who would like an introduction to the physics of flight - should visit a page called On the Wings of a Dragonfly, which gives just that. Although the creators of this page directed it at children, they explain the basics of flight in a way that anyone might find interesting and helpful.

To get additional details of the physics of flight, tour the Vertebrate Flight Exhibit at the University of California Museum of Paleontology. It goes over the basic principles of flight, including drag, lift, and thrust, and explains different kinds of flying, such as gliding or parachuting.

Beyond locomotion, the field of biomechanics studies many other things. For instance, a biomechanic might measure the strength of any biological material, from a molecule to a molar. Unfortunately, few pages on the Web examine the basic research side of measuring strength. Nevertheless, such measurements often lead to various medical applications, especially ones involving bones.

The Berkeley Orthopaedic Biomechanics Laboratory, for example, applies "the principles of engineering mechanics to understand basic biological processes and mechanisms related to the structure and function of bone." Visitors can explore a variety of ongoing research projects at this site, including one called Prosthesis Design. This project uses finite element models of hip implants to test how a specific prosthetic device will perform. Then, the design of a device can be changed and retested to look for ways to make it perform better, or last longer under the repeated stress created by the rhythm of walking.

Still, some areas of biomechanics seek even more stress by studying sports. Sportscience will help one keep track of general information on the biomechanics of sports. It posts articles about the science of all kinds of sports, as well as links to meetings. Other sites provide more information on specific athletic events. Baseball, for instance, might never seem the same after a tour of the Biomechanics of Baseball Pitching at the Johns Hopkins Orthopaedic Biomechanics Laboratory. Here, a sequence of frames shows a player's skeleton during a windup and pitch. In addition, colored arrows show the arising forces. If one can wait just a few minutes for a download, one can watch an MPEG movie of this pitching skeleton; the skeleton winds up, rears back, and fires the ball home. All the while, arrows show the changing forces during the pitch. Finally, the virtual camera spins around to show the pitcher from every angle in a 360 degree perspective.

A thorough review of the Web might turn up pages that post biomechanical information for most any sport. For example, one page shows the forces involved in pole vaulting. The International Society of Biomechanics in Sports helps surfers find such links. It also hosts a newsletter, and can connect visitors to the pages of other related societies.

In fact, one can spend hours just exploring the sites of societies dedicated to biomechanics. Here are a few of them: the American Society of Biomechanics, the Canadian Society for Biomechanics, the Deutsche Gesellschaft für Biomechanik, the European Society of Biomechanics, and the International Society of Biomechanics.

A tour of the biomechanical sites on today's Web might not unveil all of the mysteries behind the toughness of trees, the flight control of animal aviators, or how ocean creatures stay put beneath the surface of a rough sea. Nevertheless, such a tour serves up a basic introduction to this field, giving everyone the chance to take a walk on biology's mechanical side.

Biomechanics World Wide - this list of links leads visitors to home pages of biomechanists throughout the world, and offers pages grouped by topic, such as "gait and locomotion," as well as journals and societies.

Glossary of Biomechanical Terms - this page lists common biomechanical terms, from accelerometer to work, and gives a basic definition of each.

Biomechanics Yellow Pages - links to companies offering biomechanics research tools, including forceplates, motion-analysis software, and various transducers.

BioMechanics Magazine - an online edition with access to some articles, plus extensive links to other biomechanics-related sites.

Biomch-L Newsgroup - gateway and archive for this email list on biomechanics.

Web sites mentioned in this column:

• Biomechanics (Vassar College)
• Gait Analysis Page
• Gait and Clinical Movement Analysis Society
• On the Wings of a Dragonfly
• Vertabrate Flight Exhibit (University of California Museum of Paleontology)
• Berkeley Orthopaedic Biomechanics Laboratory
• Sportscience
• Biomechanics of Baseball Pitching
• International Society of Biomechanics in Sports
• American Society of Biomechanics
• Canadian Society for Biomechanics
• Deutsche Gesellschaft für Biomechanik
• European Society of Biomechanics
• International Society of Biomechanics