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Facts of the Matter Richard Brill |
ASSOCIATED PRESS
When horses are galloping, they are either fully airborne -- as Empire Maker, above right, was at the Belmont Stakes last Saturday -- or they have just one hoof touching the ground, as did Ten Most Wanted, center, and Funny Cide.
Motion analysis finds
many modern applicationsOne of the most beautiful sights in the natural world is a horse in full gallop. The horse is engineered by evolution to run, and the beauty of it inspired artists for centuries to study the motion as they tried to capture the image on canvas. Yet the details and complexity of the motion escaped analysis until the final quarter of the nineteenth century.
The problem was that horses' legs move too fast for the human eye to capture their exact sequence. There were many theories and much discussion about the details of the motion, professed by generations of philosophers, artists and other observers of nature. Some held that there were brief periods when all four hooves were off the ground, while others believed a galloping horse had at least one foot on the ground at all times.
Artists portraying the gallop were faced with a choice of how to freeze the motion in ways that were esthetically appealing but also realistic-looking. The convention was established to depict a horse in full gallop with front and rear legs fully extended as if flying. In reality this doesn't happen, and watching a horse run it is apparent in retrospect that the legs are never splayed out that way.
It wasn't until the invention of the camera that the debate could be settled. Documented in a famous sequence of photographs published in 1877, Eadweard Muybridge set up a series of stop-motion cameras and trip wires to capture images of a horse that galloped past a row of a dozen cameras. The photographs showed not the idealized and graceful motion that artists depicted, but instead a less esthetically appealing skipping motion. When painters began to incorporate the actual motions in their paintings, critics didn't like it, complaining that something didn't look right.
Muybridge's lesser-known contemporary Etienne-Jules Marey developed a method of exposing a sequence of photos on a single plate, but the defining work of slow-motion photography was that of Harold Edgerton, who developed high-speed cameras in the 1940s that could expose millions of frames per second to virtually stop motion.
Although Muybridge was not the first to study gait, his analysis of the motion of the horse and other animals, humans included, spurred the development of biomechanics and motion pictures. Aided by the computer, biomechanics has found applications in many areas today in science, medicine, art and entertainment, to name a few.
In orthopedic medicine and rehabilitation, motion analysis helps to guide the mending process of an injury. In manufacturing or business, motion analysis enhances the efficiency of certain jobs or tasks. In sports medicine, motion studies improve performance in a variety of sports. Motion analysis has aided in the development of a space suit for NASA, and in the film industry, motions of various kinds are digitized and used in computer animation.
As it turns out, the gait of a horse is very different when walking, pacing, cantering, trotting and galloping. Not only does the sequence of movements of the legs differ, but the efficiency of energy usage is also different. The latter is also true for the rider. Being familiar with the rhythms of the different modes is important to riders who must adjust to it, to become "one" with the horse and to be in resonance with it.
Beginning riders get bounced around until they learn to anticipate the movements of the horse.
Anyone who has watched a western movie is familiar with the three-beat, broken rhythm of the canter (mostly added to the movie in post-production). The trot, by contrast, is a faster gait in which the legs move in diagonal pairs, while the pace is a gait where the legs on one side are moving roughly in synch. The gallop is a coordinated skipping motion that alternates between front and back legs; most of the time, the horse is either flying or has only one foot touching the ground. This allows four power strokes per stride, and also explains why a horse with one bad foot cannot gallop, since each of the four legs supports the entire weight of the animal at some brief time during each stride.
Motion analysis of contemporary thoroughbreds plays a diagnostic role from the beginning. Colts are routinely filmed at the trot since it is inherently symmetrical, and signs of lameness are exaggerated compared with the walk. Upon closer analysis the diagonal limb pairs in the trot do not strike the ground simultaneously; the rear leg normally precedes the front at both impact and lift-off. In a horse who is lame, the sequence and timing may differ slightly. This can be corrected in some cases, or fine-tuned to increase the efficiency, and therefore the speed, of the horse.
The science of gait analysis is not yet sufficiently advanced to the point that it can routinely pick future Triple Crown winners, but it holds great promise as a performance predictor and diagnostic aid. Biomechanics and motion analysis have many uses above and beyond thoroughbred racing. Paleontologists use biomechanics to help them understand the motion and running speeds of long-extinct dinosaurs and their roles as either predators or prey.
As NASA scientists searched for an efficient style of locomotion on the moon, Apollo astronauts tried many different gaits. The most preferred one was, surprisingly, skipping. It turns out that body mass to bone strength ratios do not favor skipping of large critters such as people. Preschoolers skip, and it is an efficient means of transport, but as we grow our bones bear a proportionately greater load and skipping soon becomes more of a chore.
But in the low gravity of the moon, the "skipping load" on the bones is tolerable, even wearing the heavy life support and communications backpacks, and is the most efficient pedestrian mode for extraterrestrial strolling.
Film animators have the daunting task of modeling animals, characters and caricatures of various kinds in motion, so they must study the ways that different animals move and the differences between them. Modern animation software uses the digitized results of motion analyses to plot the complex motions of the myriad creatures that fill our movie and television screens. Many of the techniques of computer animation rely on Muybridge's stop-motion concept. His technique was applied in reverse in early rotoscopes and helped to conceptualize the idea of "moving" pictures. His "row of cameras" method is used today, albeit it in slightly different form, in creating the stop- and slow-motion sequences shown in "The Matrix" and other recent movies.
We take walking and running for granted, having learned it long ago, our own bumps and bruises from errors during the learning process erased from memory. That we can do it at all while balanced on two rather spindly legs is remarkable. That we can do it without thinking about it signifies our link to other creatures with legs. That we can study, analyze, perfect, copy and apply it in engineering by using a combination of art and science is nothing short of amazing.
We could all be a little smarter, no? Richard Brill picks up
where your high school science teacher left off. He is a professor of science
at Honolulu Community College, where he teaches earth and physical
science and investigates life and the universe.
He can be contacted by e-mail at rickb@hcc.hawaii.edu
