BEFORE we all get lost in the dust from the next army of joggers plodding by, let's put the Fitness Fad into a little historical perspective. In the past, fitness was a word generally reserved for horses. A few stubborn athletes were expected to persist in their sporting ways into later years. But the number of jocks keeping fit was no more nor less than the number of eggheads who went on reading books - real books - after they had finished school.
We're talking about a couple of life's distinct minorities.
In the past, any socially acceptable exercise resembled golf, if indeed it was not golf. The huffing and puffing was, first and foremost, sedate. One barely needed to remove a necktie to perform.
When most adults now jogging were children, only kids under 12 ran in public. Any grown man seen on the street, picking 'em up and laying 'em down, would be arrested on suspicion of fleeing the scene of a crime.
Even professional athletes had the decency to give up strenuous exercise after the public stopped paying them for it, just as most college professors had the decency to give up reading books after finishing graduate school and getting their lectures down pat.
To continue exercising (or reading books) into adulthood has always been regarded as an aberration by the majority of sensible citizens.
Of course, not too many people nowadays get caught reading to excess. But as a research paper from First Manhattan Company of New York says: ''Fitness has spread from a small group of premier athletes to the masses.''
Fitness has spread somewhere else too - from the streets and playgrounds and health clubs, straight into the sanctity of the home. Once, no American home was complete without a game room. A game room contained a three-legged pool table (or a Ping-Pong table with no net) plus a sofa with the stuffing coming out. A game room was the place where we slouched and slumped and generally relaxed. Now the game room has been claimed as the home gym where we do none of the above.
Goodbye to historical perspective - you can't see for the jiggling.
The dreaded gym teachers of our childhood have us on the hop at last. Only they don't look like the gym teachers of our childhood. They look like Jane Fonda. Across the country, some 380,000 videotapes of ''The Jane Fonda Original Workout'' flash before our bulging eyes as we self-agitators shake and rattle our framed posters of Jack La Lanne right off the wall.
Are we really ready for our homes to be built around a gym, with a ''lo-cal'' kitchen as an annex?
Too late. It's already happened, if you believe the people who are counting the Fitness Fad in dollars and cents, like the editors at Industry Week. They report that, compared with just a year ago, Americans are spending 48 percent more on home gym equipment - treadmills, exercise bikes, rowing machines, and all the other tools that operate on us. Annual sales of products ''related to sports and exercise'' now total $26.7 billion - a figure that seems more consistent with the Pentagon budget. A four-color ad in a Sunday paper reveals that a ''complete fitness system,'' ergonomically engineered, as they say, for more than 100 exercises, has been marked down by $300.11. If you superbly conditioned sprinters hurry, you can now purchase for a mere $3,199.88 this instrument that looks like one of the more fiendish devices from a medieval dungeon - with a chrome job.
The Fitness Fad is getting to be an old joke. But do we realize how far the joke has taken us?
What exactly are we doing besides exercising when we buy leotards, headbands, and ''aerobic'' shoes (sales up 50 percent in 1984), then nearly drop from exhaustion and near-bankruptcy?
In our solitude (just me and my torso), have we discovered that lifting weights is a simpler balancing act than dealing with other people?
Are we escaping an unmanageable world by reducing existence to so many push-ups, so much toe-touching?
Who knows? But an obsession with the Perfect Body is an idea that affects a lot more than the body. As our physical proportions improve, the proportions of our lives are getting a little bizarre. Before we all go jogging off into the middle distance, nibbling our sunflower seeds, perhaps we should ask ourselves: Will the '80s pass into history as the decade when we made living ''naturally'' the ultimate artifice?ay and Friday column