Just because it's the beach season, there's no need to spend your day lying around in the sand hiding a physique in need of a good workout. The beach is a natural gym and the sand and the water are nature's own Nautilus equipment.

"Running a mile in the sand is much harder -- perhaps three times harder -- than running on a normal surface," says Kathy Zarcadoolis, fitness coordinator for the New York City Parks Department.

To Zarcadoolis, the seaside is the perfect place for a variety of outdoor workouts. For instance, walking in water is fine for strengthening the calf muscles and strengthening tendons in the lower leg. She also recommends standing in water at chest-level and pulling down with the arms, the palms of the hands down and fingers stretched out to build upper-arm muscles.

"It's a good way to start a program of exercise and still be in the social swim," Zarcadoolis says.

Fitness expert and trainer David Essel, producer of "The Beach Workout," a video filmed on a Florida strand, is even more enthusiastic about the shore.

"Walk a mile in knee-deep water and you'll have a workout equivalent to running a mile on dry land and will have burned about 130 calories," he says.

Jesse recommends walking straight ahead for 100 yards, then walking sideways for 20 steps, alternating from the right to left side. The sideways walk strengthens muscles around the hips. Walking backward can be added to the routine to beef up the hamstrings and the muscles around the knees.

Another Essel trick is to stand chest-deep in water and use an empty 1-quart plastic milk jug as a float that is pushed down under the water as far as it will go. This is much like doing push-ups and will strengthen the pectoral muscles.

To work the triceps, the arms can be extended in an "L" position and the jug is pushed down and then eased up to the water's surface. You can do as many reps as you want and will get a workout similar to one on a Universal-type gym machine.

Essel cautions persons in less than top condition not to run in the sand, because the instability of the surface makes injury more likely. But he does recommend the sand for anyone with a tendon problem in the lower legs or feet.

"If you use your toes to pick up sand it will do wonders for inflamed tendons," Essel says.

Another partisan of the beach is Jane Katz, author of "The Water Workout."

"Exercising on the beach is a win-win situation," Katz says.

Walking in the sand or water 3 or 4 inches deep offers unique resistance, Katz says. She says jogging and walking in water for an hour can burn up 500 calories.

Stretching while lying in the sand before a workout also offers good benefits.

The soft sand acts as a support for the body and since the sun turns the beach surface into a kind of natural heating pad, it warms up muscles and cuts down the possibility of injury during exercise.

Katz's favorite exercise is done while sitting on the beach, with legs in a "V" position. The legs are flexed and the heels dug into the sand. Then a person can move both legs in semi-circles.

The exercise is "almost magic" when it comes to strengthening the knees. If a person tires of just making semicircles the heels can be used to inscribe other designs in the sand. In fact, Katz says that doodling in the sand can be used to build up the entire leg from ankle to hip.

All three shore mavens caution that the one essential piece of equipment for beach exercise is sunscreen -- a severe sunburn can sideline an athlete for weeks.