From aqua cycling to aqua yoga, water-focussed workout classes have become more and more popular in recent years. The best option for a low-impact workout is aqua aerobics, because "the water removes much of the strain on joints that accompanies typical land-based aerobics," says Ashley Reaver, RD, ACE-CPT, a certified personal trainer in Oakland, CA. "There is also added resistance when moving limbs in water, which can help to keep your heart rate in cardio range."