BODY WATCH : High Water Mark : They’re doing <i> what </i> at 5:30 in the morning? Despite exhausting workouts and coaches’ taunts, rowers are devoted to the sport--and its health benefits.

It is 5:30 in the morning and today we are feeling the magic. The sun is beginning to break over Marina del Rey, a seal pup is playing in our wake and the only sound is the whooshing of our four-oared racing shell slicing the surface of the water.

It’s not always this way. When you have four people tugging on 12-foot oars before daybreak, trying to balance a boat that is as long as a truck but barely as wide as your forearm is long, there’s going to be some discord.

Often, too, you have to contend with the admonitions of that man there in the rubberized dinghy; he is the Southern California Boat Club’s Buz Tarlow--6 feet, 4 inches and 240 pounds worth of critiques, crude jokes and sporadic praise.

But occasionally, you feel the magic, and that’s what tempers the raised eyebrows and stifled gasps of friends who ask, “You’re doing what at 5:30 in the morning?” Their surprise is understandable. Until seven months ago, the only explanation for my being up before sunrise was that I hadn’t yet gone to bed.

The rewards are tangible. Rowing affords devotees cardiovascular benefits that are unrivaled by any sport, except perhaps cross-country skiing. In fact, a standard 6,000-meter “piece” (a continuous row of about 3 1/2 miles) easily chews up more than 400 calories in just 23 minutes--compared with the 350 calories per 30 minutes a fitness runner or cyclist will burn. At the competitive level, rowers burn an astounding 1,600 calories in one hour.

The fitness benefits are certainly part of the draw, but rowing, many participants say, holds a more visceral appeal.

For Eric Fisher, a 35-year-old Los Angeles architect who rowed in graduate school at Harvard, it’s the “grace you get from doing something that requires both fluidity and strength.” For Kim Crossett, a 32-year-old graphic designer in Santa Monica who has been rowing for just more than a year, it’s a source of life lessons as well as an athletic pursuit.

“This is something that you can’t expect to be perfect at right away,” she says. “I’ve gained a lot from learning to just hang in there.”

As far as Tarlow’s concerned, Crossett’s persistence has paid off: He’s assigned her to his women’s “A boat,” a racing shell that competes against universities and other boat clubs in formal regattas held regionally and nationally. This means as many as five rows a week with Buz often in tow, eagle-eyed to the slightest imperfections in technique. At speeds of about seven minutes a mile, something as simple as how curled your fingers are on the oar handle is enough to throw off the entire set--or balance--of the boat.

Each stroke of the oar can be dissected into a hundred individual biomechanical movements. Multiply that by the number of rowers in a boat and it’s clear why Tarlow will occasionally pepper his shouted commands with an uncharacteristically soothing, “Zen rowing! Let’s see some nice relaxed Zen rowing.” Oddly, it often does the trick, as the crew surrenders to some wisdom the body has but the intellect seems to fight.

“It may be a thinking man’s sport,” Fisher says, “but thoughtfulness can get in the way.”

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Tarlow, who rowed crew for four years at Harvard and then went on to coach one of the university’s rowing programs, moved to Los Angeles in 1989 in the hope of establishing a club heavy on coaching and short on pretension. Many of his members are former college athletes, but some have never engaged in sports.

I approached him late last winter after years of having been a dedicated gym rat. Unimpressed, he chided, “If you want to stick with this, you’re going to have to get into shape.”

I quickly saw his point. So little of my gym routine translated into the athletic movements required in rowing. My leg strength was weak--more than 75% of a rower’s power is generated by the legs, which push back on a sliding seat after the oar has been placed in the water. And my level of cardiovascular fitness was not capable of the sort of hard, all-out endurance that rowing required.

Since joining the club, my workout routine has shifted dramatically. Uphill cycling, trail-running and 10 to 15 continuous sets of sprints on the famed Santa Monica steps have landed me a seat in one of Tarlow’s racing boats.

“The sport requires fierce concentration, persistence, and a commitment of time and energy,” Tarlow concedes. “But it pays back in dividends.”

He points to the bodies of rowers and to studies that show rowers not only have a low incidence of heart disease, diabetes and other ailments, but also stick with the sport well into their 60s, 70s and 80s. Watching senior-level rowers compete is a sight to behold. Because the sport is low-impact and thrives on experience and endurance over brutish strength, rowers seem to get more fluid--if not faster--as they get older.

Despite these benefits, don’t expect to see a rowing boom on the order of in-line skating or snowboarding. The U.S. Rowing Assn. estimates the number of participants at 100,000--a figure that is growing somewhat, but probably will never approach the 20 million who blade or even the 2 million who snowboard.

But rowing offers something more: moments of exquisite serenity.

On a recent post-storm Sunday afternoon, I let myself into the club and launched a one-man scull off the dock. The water was black and placid, not another boat in sight, as the sky turned from blue to orange. My pace slowed to a paddle and in the thin string of my wake a seal popped its head up and submerged, over and over, port to starboard, following me down the length of the channel.

If my experience that day had been the only thing I’d ever gotten from rowing, it would have been fine with me. Just perfect.