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cial knees to replace the diseased joints of patients with bone cancer or certain other ailments. During the transplant surgery, the doctors leave the patient's lower and upper leg untouched while they remove the afflicted area. They then cement the metallic substitute in place, retaining the body's own ligaments. Built of a cobaltchrome or titanium alloy and polyethylene, the implant owes its existence as much to engineering as it does to medicine.

LAWS OF MECHANICS

The new science of biomechanics is harvesting what we have learned in building structures from cars to cranes to

spacecraft and turning this knowledge

back into that most complex of contraptions-the human body. Biomechanical science approaches the body armed not

with traditional medical concepts but

with notions of torque, load, stress, lift

and drag. From the view of the biome

chanician, we owe our ability to move about and support ourselves chiefly to the

everyday laws that govern fulcrums, le

vers, pulleys and counterweights.

Human beings and machines are both physical structures that, if they are going to function, must come to terms with the same physical laws, says Dr. Frederick Vosburgh, of Rockefeller University in

New York City. "There is a correspon

dence between what we design and what nature has designed," he adds. "And the

key to that correspondence is that there is a selection of what works and what doesn't work in both spheres."

Scientists often find that even the most obscure of man's inventions may turn out to be little more than hand-me-down tricks long ago mastered by nature. Braces designed to stabilize the fuselage against twisting in rockets and airplanes were built and perfected only after the turn of the century. However, when Vosburgh and his associates recently investi

gated the fibrous structure of sharkskin,

they discovered that a shark's rear fins

are held rigid in almost the same fashion

as a fuselage. Aerodynamic laws, it

seems, forced human engineers to reach

the same conclusions nature did-we just

arrived at our answers a bit later.

More and more, biomechanicians are

analyzing human form and function with

the same tools used to test inanimate de

vices and using what they find to help the

human body work better. At California's

Coto Research Center, biomechanician

Gideon Ariel is employing sophisticated

electronic systems to decipher and im

prove the performance of athletes.

Currently, Ariel is designing what may

be the world's first computerized footwear-a running shoe with a microchip nestled in its sole. The chip operates as a pressure and load gauge, recording and interpreting foot impact and stride length. At the conclusion of an exercise period, the runner simply removes the device and plugs it into a home computer to learn his average speed, the distance he ran, the calories he burned and how much weight he is likely to lose.

Ariel is also one of several biomechanicians who have been using ultra-highspeed films, moving at the rate of up to 10,000 frames per second, to record acts as simple as walking or as complex as a basketball lay-up shot. He then projects the films onto a screen with a grid and thousands of coordinates. A computer can thus follow a specific spot on the volunteer's anatomy as it passes across the grid and assess how far, how fast, how efficiently and how expertly the subject's limb travels in a given instant. The device, which breaks movement and agility down into countless tiny fragments, helps distinguish previously indistinguishable elements of motion. So well does this unforgiving scrutiny work that Ariel has been asked to apply his techniques to members of several professional sports teams and even to athletes on the 1984 Olympic squad.