What if you could melt fat, tone your body and feel like a kid again—all in just 10 minutes a day? Fitness legend Denise Austin, 69, says you can, and the secret is as simple as jumping in the pool.

Finding new (and fun!) ways to mix up your workouts will keep your muscles guessing and you from getting bored and bailing on your fitness routineboth of which are super important if you want to see ...