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<br /> ACCELERATION
<br /> gear. How could receptors that arc such tern.Acceleration snaps your head back: I physiological pipsqueaks create so your neck and shoulders contain per-
<br /> much fun—and therefore so much me- haps the richest bed of proprioception 0 a
<br /> chanical sport? in your body, charged with the task of
<br /> I was overlooking muscle, and its sell- keeping your eyes level and your bal-
<br /> sort' power. Skeletal muscle is the larg- ance perfect,so that you will be ready to
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<br /> est sensory organ we have, and it reads take action no matter what kinds of up-
<br /> acceleration throughout the whole set the rest of your skeleton is being put `.
<br /> body. I never dreamed such a thing was through.
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<br /> possible. You can—you do—read acccl- Acceleration snaps everything back; `
<br /> elation right down in your little linger. you feel it just the way your face felt the
<br /> Acceleration is one of the most massive pull of gravity plus centrifugal force at
<br /> sensory experiences we ever have. the bottom of the arc of the playground
<br /> The sensors that count, acceleration- swing. At that moment gravity tugged 4
<br /> wise, are the proprioceptors—the "self- harder at the mass of your facial flesh;
<br /> sensors"—little specialized nerve end- and that attempted dislocation of the
<br /> ings that are embedded in the muscle, mass fired thousands of proprioceptor
<br /> the tendons, and the joints, that read endings in the facial muscles. It was an •
<br /> and report on body position, move- unusual feeling and you experimented
<br /> ment, and loading.They are the memo- with it. (Kids are the ultimate sensual- Imagine the neural fireworks for a
<br /> ry banks your coach was talking about ists, doing everything just to find out Formula 1 driver practicing his craft, .
<br /> • when he spoke of"muscle memory" (al- what each new experience feels like. taking all that horsepower through as
<br /> though that term is misleading). They This helps explain everything from complex a series of'patterns as the
<br /> arc the neural devices that weigh and roller coasters to teen-age pregnancies.) course can dish up. (Looked'at this way',
<br /> - judge and perceive whatever you do The same force at work on your facial, aerodynaihic bodywork is a complicated
<br /> with your musculoskeletal system, from muscles was also at work on the rest of way to increase the possible loadings, to .
<br /> . guiding a forkful of pasta safely into ' • boost the forces at work right up to the
<br /> • ' your gob, to 'catching the rear end of breakaway point:) Imagine the balanc- _
<br /> Y Indy car when it starts to break Some of us get very good ing act, the vectoring that's going on, as
<br /> loose at 220 mph. Some of us get very the driver works those tiny little con-
<br /> good with out' proprioceptors. The with our proprioceptors. trek—
<br /> good gas, brakes, gears'lo .
<br /> ones who do are usually called athletes, The ones who do are ' cut a way through all that sensation, to
<br /> of which racing drivers—drag, road, or come up with the alignments and 'ttr
<br /> round-and-round—are one special sub- usually called athletes.' rangements that will keep the car (a
<br /> category. 'Those of us who don't get __— his body) moving in the chosen dire.
<br /> • good at proprioception are called tion at the fastest possible speed.
<br /> .spectators. you, of course, giving you that sweet lit- Skill at that balancing act is usually
<br /> The way human muscle acts as a sen- de perceptual thrill, almost a sexual credited to kinesthetic sense, which is a
<br /> sor requires a kind of neural rigging thrill, that you get when your entire rather vague term for the capacity to
<br /> that would have made the late Colin body is being worked upon by forces read and react to the signals from the
<br /> Chapman proud. Muscle stays alive by larger than usual. proprioceptors. It's a sense that can be
<br /> means of a complex neural loop that Ilard acceleration is the playground improved with practice. At its higher '
<br /> connects sensory (afferent) nerve end- swing times ten, times a hundred,.,the levels it is a very acute sense indeed. It's
<br /> ings to the central nervous system and same category of forces raised 'to the sense that allows the diver to come
<br /> in turn to effector (efferent) nerve breathtaking new heights. Every ounce out of his tuck—after three and a half ;i
<br /> endings. This loop maintains in the of mass on your body is under a dislo- somersaults from 33 feet in'the•air—a
<br /> muscle a steady state of low-grade con- eating force that seems to want to pull the precise instant that will 'enable him .
<br /> traction that keeps it ready for use: mus- the muscle from your bones, to pool' to enter the water absolutely vertical
<br /> cle tone. (Muscle tone has been likened your blood and your flesh on the back-, and with minimum splash:'ft's the sense
<br /> to the idle of a car's engine.) Snip the side of your skeleton. Your propriocep- that tells the trout fisherman just whey ,
<br /> loop at any point and the muscle that it tors light up your central nervous sys- and how hard to set the hook—onithe
<br /> innervates will atrophy like that of a tern like those rows of control panels–at• basis of information gathered from nig •!
<br /> limb in a cast. Mission Control in Houston. sources other'than the Muscles of rbc
<br /> Muscle tone in turn maintains the I'm thinking of acceleration in the hand, wrist, and arm. It's the sense that 'I
<br /> stretch reflex, which is the muscle's drag-strip sense, as a straight-ahead allows the good tennis player to read—
<br /> automatic resistance to the displace- push. C/D's technical editors,who know• from the torque on the racket handle—
<br /> ment of the limb. When the doctor taps a lot more about physics than I do,'will just how far off-center the ball has met
<br /> . your kneecap, he's really stretching the tell you that in any kind of driving there the racket face (and, on'the basis of that
<br /> tendon that connects the kneecap to the arc accelerations in every direction; ac- information, to fire enough muscle fi-
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<br /> thigh muscles. That stretch fires pro- celerations in vectors and angles, side hers of the wrist and forearm +„- ;
<br /> prioceptors in the muscles that tell the loadings and (heart-stopping) unload- pensate and slam the forehand 1.1tiner
<br /> spine there's a mismatch in the length ings. There is no end to the ways you two inches inside the cross-court tine).
<br /> • of those muscles. The spine in turn can find to get your frame tossed about It is the sense that'enables the racing •
<br /> sends signals back to the muscles to and titillated by external forces anddriver to make sure that there'is som
<br /> match up their length, which signals changes of direction. Every one of them where very close to 11,500 rpm (a
<br /> make you,kick your foot. carries this kind of proprioceptive thrill. third gear) available 'to the' dris
<br /> When you twist the throttle on a nun- Every one of them cranks on all those wheels—and that the accelerator pedal
<br /> toreycle, you're changing the loadings nerve endings, pleasuring you with new has just started down—at the precise in-
<br /> On• most of your musculoskeletal sys- sensations. slant the drive wheels drift out to the
<br /> 32 CAR and DRIVER
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