IN THE SHALLOW END OF A POOL in Rancho Santa Margarita, California, former Stanford running back and current NFL free agent J.R. Lemon, 23, gasps for breath as he works out with aquatic dumbbells that look like wiffle balls with fins. Wearing matching widgets on his ankles, he thrashes his hands and feet back and forth so fast the water bubbles like a spa. Then, grabbing a thick elastic band tied to the pool ladder, Lemon leans back, loads his calves and quads, and explodes rearward before the taut band flings him back. When the 30-minute workout ends, Lemon is exhausted. "In the water, the harder you push, the harder it resists, yet I feel great—not beat up like with weights," he says. "You can't push this hard in the gym—you'll get hurt. It's definitely helping my first step get faster. Just like Marv said it would."

That would be Marv Marinovich, 67, a former Oakland Raiders conditioning coach who advocates explosive stop-start plyometric movements in lieu of conventional weight training. "Power isn't just strength, and it isn't just speed," he says. "It's strength-speed—how quickly you can apply your force. It's what you need to change direction to avoid a tackle, to swerve away from an open car door when you're on your bike." Marinovich's method exploits the principles of plyometrics: Stretching a muscle right before you contract it fires more bundles of muscles at once and capitalizes on elastic energy produced by tendons and ligaments, generating a higher jump or quicker cut than if you started from a static position. Proof that it works? Since Lemon began Marinovich's program last August, he's added four inches to his vertical leap.

Marinovich became an instant aqua convert last summer when he saw the water dumbbells made by Aqualogix. "I have seen nothing that facilitates my training methods like this," he says. "Nothing else lets you do such real-world movements." Translation: Dragged through the water, aqua-bells provide resistance in every direction. To help you reach your maximum potential, Marinovich has devised the ultimate high-performance, low-impact training plan. It builds strength, speed, agility, and power—while putting the least stress on your body. Perform each exercise in short, high-speed, back-and-forth bursts. Work until you can no longer maintain correct form, then shift quickly to the next exercise. Continue to cycle through as long as your form lasts. Do the program at least three times per week. And after you see the results, you'll have one more reason to put a pool in the backyard.

The Gear

1). Aqualogix Bells ($59 per pair) and Fins ($49 per pair); aqualogixfitness.com
2). Resistance band Inch-thick type found at any hardware store, $10
3). AQx aquatic training shoes Water-specific shoes that protect soles, add grip, and have "gills" that add resistance. $80; aqxsports.com

1. HIP FLEXION AND EXTENSION
What It Works: hip flexors, glutes, hamstrings Equipment: fins Form: With hands on the pool's edge, extend one knee up to your chest, then thrust the leg back and as high as you can, keeping it straight. Alternate legs. This addresses two of the most significant speed-stoppers in athletes: weak hip flexors and tight hamstrings.

2. THE MERMAID
What It Works: obliques, lower back Equipment: fins Form: Stand six inches from the edge of the pool in chest-high water. Hold the edge and put legs together as one unit (think mermaid). Then, bracing your hands, arms, and shoulders against the edge, swing your legs from side to side without pausing. Try to keep them parallel with the side of the pool, like windshield wipers. Swing legs as high and as fast as you can. To work the obliques at different angles, alternate between bent and straight knees.

3. SHORT KICK
What It Works: lower abdominal muscles Equipment: fins Form: Stand on one foot and lift your other foot barely off the pool bottom by slightly bending your knee. Swing the free foot forward six inches and then behind you six inches. Keep it as low as possible without scraping bottom, and move it rapidly back and forth.

4. SCISSORS
What It Works: groin, hip lateral movements Equipment: fins Form: Hang your body off the edge of the pool in water deep enough to keep your feet off the floor. Hold on with your hands, or place your arms on the edge, if that's more comfortable. Split your legs as wide as possible, as if doing a jumping jack, then quickly and powerfully bring them back toward the center and cross them, left leg in front of right. Next round, do the split, then cross right in front of left. As you alternate, put equal effort into the push-out and pull-in. Don't bend your knees.

5. TORSO TWIST
What It Works: Obliques, hips, core Equipment: bells Form: In the shallow end, stand on the balls of your feet and bend your knees. Put your arms out to your sides, with hands just under the surface. Twist your trunk and head quickly to one side while moving the bells through the water. Twist in the opposite direction. Repeat.

6. THE SPRING
What It Works: feet, ankles, calves, legs Equipment: bells, four-foot elastic band Form: For the vertical version (shown), stand straight up in chest-high water while holding the aqua-bells at your sides. Rise up on your toes. Slightly bend legs, then blast straight up like a rocket, with feet leaving the floor. Land back on your toes and blast off again and again. For the horizontal option, tie the band around the pool ladder in any depth of water. Hold on to the band with both hands a foot apart at waist level. Lean back with face up and put your feet against the pool's edge. Aggressively push off the wall with your toes, staying off your heels and midfoot altogether. Repeat.

7. CROSSOVER FLY
What It Works: arms, chest, shoulders Equipment: bells Form: Standing in the middle of the pool with water at chest level, hold the bells in each hand, with arms stretched horizontally at the sides and the bells just under the water's surface. Holding arms and elbows with a slight bend, sweep arms forward and cross them in front of your body. Then sweep them backwards quickly. On the backswing, push your wrists against the resistance and bend your elbows, which allows the shoulder blades to converge, giving you greater range of motion.

8. THE PRISONER
What It Works: wrists and hands Equipment: bells Form: Squat in the shallow end of the pool so the water is chest- to neck-deep. Hold an aqua-bell in each hand and place your hands in front of you at navel level, elbows firmly at your sides, bent 90 degrees. Your hands should be only an inch or two apart, like you're wearing handcuffs with one palm up and one down. Keeping your hands the same distance apart, elbows still at your sides, move hands as if tracing a sideways figure eight in the water, forming circles about the size of a volleyball. Your elbows should bend and open but not leave your sides. If moving two arms at once is difficult, work one at a time.