For weeks she had run along her city streets, "hitting the wall" at a mile and a half, fighting a stomach cramp here, tugging at her shrunken shorts there.

She had dutifully trudged along, expecting at any moment to experience the "high," the sense of well-being, or at least one moment when she would think of something other than stopping.

The jogging books had told here that there was pleasure in this process. She was sure that the only thing that stood between her and the "high" was the weather or the asphalt or the hills.

But now, here she was on this perfect dirt road, under this perfect sky, on this perfect 75-degree day, struck with a perfectly obvious fact: She was miserable. In one flashing moment she knew what so many others before her had so long denied. She hated running.

At that point there were only two alternatives: to throw herself upon the nearest chaise, never to rise again, or to accept running for what it was - an endurance contest, a fitness regimen. On that long, lonesome road, she continued her pursuit of unhappiness.

At least, as she counted her breathing like a Lamaze patient, she was not alone. In a country critized for self-indulgence, it seemed that half the people were committed to this sort of miserable self-discipline.

Physical ascetism, self-denial, had become positively trendy.

Among the chic-est people, Perrier water had replaced Cutty Sark, running had replaced lounging, yogurt dips with vegetable slices had replaced sour cream dips with potato chips. To a foreigner, the whole scene must have looked a bit odd. Here, in a country full of cars, millions of people had taken to running. Here, in the breadbasket of the world, millions more are constantly dieting. Nearly the whole republic was into a regimen of one sort or another.

She had this peculiar feeling, right above her shin splint, that people were artificially reproducing what was once a natural necessity. They had turned occupational hazards into recreational ones.

After all, the people who work with their bodies for a living don't lift bar-bells in their spare time. The people who dig coal don't go home at night and ride exercycles. It's the white-collar workers, the sitters of the world, who had made James Fixx a rich man.

It is, furthermore, the great-grandchildren of the pioneers and frontiers-man who now pay to spend their vacations going Outward Bound. It's the descendants of overworked farmers who join exercise clubs. Endurance, once a necessity for survival, was now a matter of willpower.

Maybe there was rebellion against easy modern living, a kind of pain-seeking. She didn't want to get puritanical about this, but it seemed odd. Just as religion had given up self-flagellation and fasts, the secular world had taken them up with a vengeance. It was as if people suspected deep down that comfort was bad for the body, and indulgence weakened the spine.

The old prohibitions were, of course, changing. They were now delicated to the purification of the body. People who were once told to have sex only on Saturday were now told to have bacon only on Sundays. People who once mated for life now struggle to keep the same measurements for life.

In many places, refined sugar had been given up for an indefinite Lent. Cholesterol had been declared unkosher. Avocados had become the forbidden fruit of the dieter.

People all around her counted their calories and their mileage with the obsession of sinners. They did penance for too many of one, with more of the other.

Well, she refused to make a hair shirt out of a half-time or even two miles. Perhaps it was a law of human physics to seek some kind of balance - to seek new restraints, tests, rules, when the old ones loosened. Perhaps there's something pleasurable in proving ourselves as well as being ourselves.

Running was a hateful thing to do. But it was a great thing to have done. As she sprinted the last tenth-mile she remembered the best part: finishing.