In the sparkling sunshine yesterday, runners at the finish line of the Boston Marathon said they had taken very much to heart the new warnings about drinking too much water during a race. ”I was conscious of not taking huge amounts of water,” said Ian Bloomfield, 52, of England, who pronounced himself ”quite pleased” with his time of 2 hours 45 minutes. ”I was very aware of hyponatremia,” the potentially fatal result of overhydration.  Brian Paff, 24, of Chicago said he had had hyponatremia in a college race. ”I passed out from it,” he said. Yesterday, he was careful not to drink too much.

This column is for everyone who hates to exercise, or would like to exercise, sort of, but really, truly, deeply believes they don’t have enough time or just can’t do it.

I have been standing on my head, off and on, for about 35 years now,  as well as sitting cross-legged breathing through one nostril at a time, and — my favorite — lying flat on my back, utterly relaxed, in the so-called “corpse pose.”I am, in other words, one of the 15 million Americans who, according to a Harris Interactive Service Poll done in 2003 for Yoga Journal, have fallen in love with this ancient Indian practice that’s part meditation, part exercise. To the cognoscenti — and our numbers grew by nearly 29 percent between 2002 and 2003 — yoga is a pleasant practice that seems to enhance physical and emotional strength, flexibility and balance. But does it?

It can be rather bewildering, frankly. We all know by now — duh — that we’re supposed to exercise.But how? By lifting weights? Or running? How much? A short walk from the parking lot to the office, or miles and miles a day? How often? Once a week on Saturday mornings, if someone else can watch the kids, or every day? How hard? Til we’re a breathless, sweaty mess or just pleasantly glowy? And most of all, in our crazy, overscheduled-lives, when?

What this fat, out of shape country needs is a Diet and Exercise Czarina. I hereby volunteer.

First, let’s get two philosophical things straight. Eating too much and exercising too little is obviously a matter of individual responsibility. Nobody’s force-feeding us, or tying us down so we can’t exercise.

Hardly anyone thought it was possible for a human being to run a mile in less than four minutes – until Roger Bannister did it in 1954. Within 3 years, nine other men had done it, too.

There we stood in our color-coded bathing caps, 1336 women — nervous, excited and all lined up in “waves” on a recent summer Sunday morning on the shores of (I kid you not) Lake Chargoggagoggmanchauggauggagoggchaubunagungamaugg in Webster, MA.

Kelly Hall, 34, was in fantastic shape, routinely biking 100 to 200 miles a week in preparation for last year’s AIDS Ride from Boston to New York. Usually, she trained with other riders, who made it a point to take food and hydration breaks. But one day last June, Hall, a strategic planner at Partners Community Health Care in Needham, decided to ride alone, despite the 95 degree heat.

Remember how good it used to feel, hanging out in the sun, letting your face acquire that nice, ruddy glow?

Then came all those depressing public health messages telling us that the sun was dangerous, that we should feel guilty about even the slightest tan.

Marybeth Turner, a 35-year-old Lexington mother of two young children, has great legs. And arms. And abs. And strength. And balance. And endurance.

Perhaps not surprisingly, given all that, she also has a personal trainer, in her case a huge, gentle guy named John Damon, co-head trainer at the Mt. Auburn Club in Watertown.