The key is to start slowly. The general rule is to increase your time or distance by no more than 10% each week.
"The reason we make that suggestion is not because the heart and lungs can't handle it, but the joints and muscles are a little slower to adapt to the stress of vigorous exercise," Stuhr says. Too much too soon, and you can develop tendinitis or a variety of muscle or joint problems.
Equipment: It's important to get a good pair of running shoes, and, for women, a quality sports bra. Pay attention to the surface on which you run. Paths and grass are softer, but they're uneven and could have holes. Concrete is harder, but good shoes help absorb shock.
Pros: Running is an excellent cardiovascular exercise. A 150-pound woman can burn 306 calories running for 30 minutes at 5 mph (a 12-minute mile). A study published in the Archives of Internal Medicine in 1999 found that aerobic exercise like running may be as effective as medication for treating depression in some people.
Cons: Running can be hard on muscles and joints and can cause injuries such as shin splints and tendinitis.
Not only is bicycling an excellent cardiovascular exercise, but you can really explore your community by cycling to different neighborhoods or in parks, bike paths, or trails. Many people cycle to commute to work.
While running tends to target the hamstrings (the muscles in the back of your thighs), cycling uses the quadriceps (the muscles on the front of the thighs) more.
It's important to make sure your bike is fitted properly to your body; otherwise, you'll put too much stress on your back or knees.
"I recommend finding a bike shop or a demo program where you can try a bike out," says Tonya Laffey, a professional mountain biker and founder of MTB Chick Racing. "I would highly recommend getting a fit kit, which measures you for the bike."