AMERICA IS ON a physical fitness binge and book-

stores are bulging with books on an infinite variety of exercises. Everyone, it seems, wants a quick fix on better fitness. Do these books help? Alas, most of the half a hundred I've read off current shelves are long on hype and short on content, products meant to meet, not to instruct, a market. And through a sort of Gresham's Law they inexorably drive good books out. Despite this, some excellent books survive to promote fitness and provide an indication of the state of the fitness art now in America.

Physical fitness may be defined simply as efficient functioning. Both the massive Encyclopedia of Sport Sciences and Medicine, sponsored by the American College of Sports Medicine (Macmillan, $39.95)--the Bible of the field, with over 1,000 articles by experts--and C.T. Kuntzleman's The Physical Fitness Encyclopedia (Rodale, out of print) delineate its parts as motor fitness, physique, organic health, and vigor. They also point out that physical fitness is but one aspect of total fitness: others are emotional, moral, intellectual, and social fitness. One can be physically fit and lack total fitness (a current tennis champion is certainly more physically than emotionally fit).

The fascinating Exercising for Fitness, by C.P. Gilmore and the editors of Time-Life ($11.95) quotes a Louis Harris poll in 1978 that found that nearly 60 percent of Americans 18 years of age or older exercise two and a half hours or more each week compared with 24 percent two decades earlier. But this strenuous activity may only reflect good health--not create it. There's no conclusive scientific proof even that it helps you live longer. All it really guarantees is that you'll die healthier than most folks.

John Lenihan's fine Human Engineering (Braziller, $7.95) concludes that the body is a masterpiece of bio-engineering. Made from the most unlikely materials --grit, glue, jelly, and soup--our bodies are so brilliantly designed that no man-made computer or machine can match them. But Lenihan finds two flaws: an inadequate blood supply to the heart muscle and disc problems caused by rewriting the original specifications (the change from four legs to two) without revising the design. His book is squarely on the mark and is a worthy sequel to Adolphe Abrahams' The Human Machine (Penguin, out of print), if not nearly so well written.

Kenneth Cooper's Aerobics (Bantam, $2.50) was the catalyst for the frenzy of exercise, particularly jogging, sweeping America since the '60s. By putting stress on the cardiovascular system causing increased oxygen consumption, his program overcame the heart-blood defect limned by Lenihan. Cooper favored vigorous activities like running, cycling, swimming, and walking, but disdained weightlifting, calisthenics, and diet. His view that physical fitness is best measured by oxygen consumption may be correct, but because it doesn't consider important variables such as relaxation, strength, and calisthenics, it remains only a partial response to better health.

Following Cooper came George Sheehan, James Fixx, and a rash of other runner writers. Fixx's best-selling The Complete Book of Running (Random House, $10.95) has been succeeded by a second book by the same writer, now yclept "Jim," who gets positively gushy on the mystique of the "high" encountered in jogging. A runner before this fad started, I returned to walking when I saw the hated army "doubletime"-- which is all jogging is--becoming an obsessive drive instead of a useful value with mainstream Americans. I still believe that rational jogging can be beneficial, but excessive running on polluted streets in all weathers is downright dumb. Churchill was speaking only of war when he said, "Nothing succeeds like excess."

Judging from the spate of new books on the subject, walking is approaching jogging as a mass exercise. A good thing, too. It is superior to jogging on several counts: though it takes more time (what do we do with all the time we save?), it is better exercise. It permits change: you can relax, think, whistle, sing, smile (have you ever seen a smiling jogger?), or stop to look and listen to nature steadily and whole. The books by Bill Gale --The Wonderful World of Walking (Morrow, $10.95)--and John Man--Walk! (Paddington, $10)-- are breezy, easy-going treatises on the ambling art that provide useful programs and incentive for all ages to try the medicine of solvitur ambulando, "sorting it out by walking."

Choice describes the hefty, well-illustrated manual, The Complete Encyclopedia of Exercises (Van Nostrand Reinhold, $9.95) edited by Hope Cohen. It covers the gamut of exercise, avoids dogmatism, and is genuinely interesting to read and use. The notion that aerobically excellent skipping rope may be as boring as running in place is scotched by Curtis Mitchell's bouncing treatise The Perfect Exercise: The Hop, Skip, and Jump Way to Health (Simon and Schuster, $8.95): his program seems sensible and good fun. Renate Zauner's Speaking of: Backaches (Consolidated, $2.95) adequately covers the field of backaches but neglects to say that swayback (lordosis) is caused as much by pushing out the chest muscles (pectorals) as by weak abdominals, and that soft mattresses produce as many back ills as poor posture.

I'm speaking of mass fitness, not the varsity-pro variety. Too many athletes, forgetting their earlier disciplines, go to pot (even that all-round athlete, Tarzan, in later life smoked, drank, and even got a driver's license!). And many older folk reflect the sentiment expressed by sportswriter, R. Vidmer, "Hell I should have been dead 20 years ago. If I'd known I was going to live so long I would have taken better care of myself." It's never too late: fitness is for the old as well as the young. Walter Noder's terse Speaking of: Fitness Over 40 (Consolidated, $2.95) addresses this aspect felicitously. While boosting the aerobic benefits of graduated exercise, he refuses to discard calisthenics. With Cooper and others, he finds weightlifting of little benefit for seniors (even for younger people it too often produces as much narcissism as strength).

Exercising for Fitness notes that vigorous exercise can be overly tense and so brings relaxation into it. For thousands of years two Asian methods--yoga from India and Tai-chi from China--have claimed to bring better health (you don't have to be sick to get better). Yoga is well-known, Tai-chi, less so. "Slow up, slow up," Talleyrand told his coachman, "I'm in a hurry." Tai-chi answers the Coopers and the Canadian 5BX'ers and others who think efficiency comes from compressing time, by letting time have its due. In Catch 22 Yossarian liked Clevinger because he was so boring. Without being boring, Tai-chi slows the old world down. Like yoga, it is a holistic exercise emphasizing relaxed muscles--anxiety, as Kuntzleman points out, can't coexist with complete relaxation of the sketelal muscles--through a series of postures and movements, correct breathing, and a quiet mind. Both are thriving today in America. Neither is effortless--Exercising errs on this--they are rigorous regimes that only appear effortless (effortless exercise is like saying a foodless meal). The volume by Lilias Folan of TV fame, Lilias, Yoga, and Your Life (Macmillan, $8.95), presents hatha yoga in a lively and instructive way, with, predictably, too much Folan. To get at its innards, you really have to go back to B.K.S. Iyengar's Light on Yoga (1966) or K. T. Behanan's Yoga: A Scientific Evaluation (1937). Tai-chi literature is more sparse, T'ai-chi (Tuttle, $15) by Cheng Man- ch'ing and myself being considered the best of an uneven lot. The book issued from China Simplified Taijiquan by th."

e China Sports Editorial Board--the first published in English--is terse and excellent.

The fine volumes by J.C. McCullagh--Recreation Alternatives: Ways to Play (Rodale, $6.95) and Terry Orlick--The Cooperative Sports and Games Book: Challenge Without Competition (Pantheon, $4.95)--are alike in viewing the search for fitness as fun, cooperative, needing no winners (why this fetish for winning in our culture? Life is a losing proposition; no one ever got out of it alive). McCullagh emphasizes the utility of nature, exercising on woodland paths instead of concrete, and a togethering in free form games everyone can play without the vexing stress of over-competition. Orlick follows a similar path with a program for all ages, drawn from games around the world, a system pivoting on play. We need more of this kind of book.

Many of these books include advice on diet. Food is fuel: it matters. A Zen monk in Tokyo told a friend of mine in response to his question of what the monk ate, "Anything edible." L.E. Morehouse and L. Gross take the same sane tack in their book, Maximum Performance (Pocket, $2.95). The Rodale Cookbook (Rodale, $10.95) by Nancy Albright is an excellent one for meat-eating and vegetarian exercisers alike, while Vic Sussman's The Vegetarian Alternative (Rodale, $6.95) is an exceptional and undogmatic exposition of the vegetarian persuasion. Finally, the best eating rules I know are: don't eat unless you're hungry, don't eat too much--especially meat--and eat slowly. Vintage instructions: they were offered over 60 years ago by Bernarr MacFadden.

But with all this flux are we fitter than we were 50 years ago? Fatter but far from fitter, I'm afraid. Recent data show 24 percent of American women and 14 percent of men are obese--reversing data of a decade ago. So what we may be seeing in the frenzy for fitness is the truth of G.K. Chesterton's observation, "When a man's body is a wreck he begins for the first time to talk about health." In the '20s and '30s, despite the Great Depression, we worked hard, enjoyed a rough plenty, and had much less indigestion and neuroses than now. Today, with the shift of population from the land to the city, from personal and physical to automated and mental labor, from rooted families to ephemeral liaisons, and from too little leisure and disposable income to too much, many are doing regular exercise simply to mitigate high-on-the-hog dissipation. But if we are indeed in retrograde, perhaps instructive books on fitness will help stay the slide.