You’ll be drenched after this workout, but it may not be sweat. If you need a nasty workout for your lungs (and more of your back than you may think), then hit the pool for some laps. You can either do interval work in the pool, swimming for, say, 100 meters, then resting for a minute and repeating 10 times, or you can just swim a steady distance (think 2,000 meters).Either way, it’s a solid workout, and it’s low-impact to boot, sparing your joints and tendons from the wear-and-tear that comes with many other workouts.