Best Cardio Ever: 15 Ways to Make It Really Work

Avoid the Achy Breaky

"You can become a faster -- and healthier -- runner by cross-training, because you're strengthening weaker muscles," says Holland. "Cycling is a great cardio complement, because it works your quads, and running emphasizes your hamstrings."

Add a Pilates or yoga session into your weekly routine. "Runners tend to have really tight hamstrings and are usually pretty inflexible," says Holland. "Pilates and yoga are safe ways to limber up."

Just two 15-minute total-body strength-training sessions per week can make your muscles stronger and less susceptible to injury when running or walking, says Holland. Include some balance-building moves, such as single-leg squats or deadlifts, in the mix to help prepare your body for the uneven terrain outdoors, says Bob Seebohar, RD, endurance coach and sport dietitian for the U.S. Olympic Committee.