For most people a pool is either a place to log laps or a perfect spot to lounge. But it can be much more: Add a set of dumbbells to the equation, and you can turn a pool into an all-in-one training zone.

Ancient Hawaiians may have been the first to develop strength training in water. They would take large rocks into the sea and carry them while they swam along the ocean floor. It’s a brilliant technique, because it removes any injury-inducing impact from a workout, and it gives you better results than strength training or swimming alone. (A weight that feels manageable on land takes far more effort to swim with underwater, and it boosts your heart rate faster than a freestyle stroke.)

Inspired by the Hawaiian method, I designed the five exercises below to be a full, efficient cardio-and-strength routine. Try it with weights that seem too light at first – you’ll be surprised how challenging these moves feel with added resistance from the water.

Dolphin Jacks
Stand in about eight feet of water, fully submerged, holding a light dumbbell in each hand (try 10-pounders), arms out to sides, feet on the pool floor. Explode up, bringing arms down to your sides as you break the surface to take a big breath. Exhale, sink back under the water, and repeat. Do 25 jacks.

Ammo Box
Hold a 20- to 25-pound dumbbell tucked into one arm like a football, and swim under­water – propelling yourself with your opposite arm and both legs – across the width of the pool. Set the weight on the pool’s edge, switch hands, and swim back. Repeat once.

Sea Horse
Stand in the water so that your head is above the surface, and place a 15-pound dumbbell between your thighs. Squeezing the weight to keep it in place, raise your legs straight out in front of you so you can see your toes, and swim forward across the width of the pool and back using only your arms.

Cell Phone
Stand at one end of the pool raising a 10-pound dumbbell overhead with one hand. Sink underwater and swim forward as far as you can while keeping the weight above the surface (as if it were a phone). Stand, switch the weight to your other hand, and repeat once.

Killer Lunges
Stand submerged in the deep end, a 20-pound dumbbell in each hand, right leg lunging forward. Push off the floor to explode up and break the surface. Take a deep breath as you scissor your legs to land back on the floor with your left leg lunging forward. Repeat quickly, aiming to do 20 lunges on each leg.

The Rules of Underwater Strength Training

Get the Right Dumbbells
Use rubber-coated weights. They won’t rust, and they’re less likely to dent the pool floor or sides if you bump them.
Wear a Mask
It keeps visibility clear and stops water from going up your nose.
Don’t Drop the Weights
Same as in the gym, dropping dumbbells isn’t just obnoxious, it’s dangerous. If you’re feeling fatigued, gently set the weights on the pool floor or along its edge.

– Laird Hamilton

Credit: Photograph by Peter Bohler