Biking and running may both work your leg muscles, but they won't shave off the fat. In fact, exercise does not directly remove the jiggle from any particular area. Before throwing in the water bottle, however, consider that either exercise is a fantastic way to burn calories, helping you slim down all over. Pair the activity with a healthy diet, and you're well on your way to a trimmer body with more slender legs. Plus, you'll add muscle tone for shapelier gams.
You may swear you feel the fat melting from your legs as you exercise, but weight loss only happens with a calorie deficit. To drop a pound of body fat, you must take in 3,500 fewer calories than you use for energy. A safe rate of loss is a pound or two per week, which translates to a deficit of 500 to 1,000 calories per day. You can achieve some of this with exercise, but the fastest way to trim down is to cut calories. Choose smaller portions of low-calorie foods to lose the fat for good.
Because fat loss is all about calories, whichever exercise burns the most will naturally be most effective. But exercise only works if you do it regularly, so the best choice is the one you enjoy most. And luckily, biking and running are comparable in calorie burning -- it all comes down to how much energy you put in. During a 12- to 14-mph bike ride, a 155-pound woman burns about 300 calories in 30 minutes -- the equivalent of a 5-mph run. At 16 to 19 mph, the same woman can bike off about 450 calories in 30 minutes; roughly the same as a run at 7 mph.
Because both exercises burn ample calories for fat loss, other factors may determine your choice. Biking requires a bicycle, helmet and apparel, while you only need the apparel to run, making it more economical. Biking may also be less safe if you're stuck on busy roads or get caught in a construction zone. Running, on the other hand, may be too intense to maintain at first -- you could need to walk for a while to build stamina. Rushing into a running routine can also lead to shin splints or other injuries, because it's so high-impact. And if you're forced to run on hard pavement, you may expose your body to unhealthy impact levels.
Whichever exercise you choose, you'll reap the rewards of a killer cardio workout. As aerobic activities, running and biking both strengthen your heart, allowing it to pump blood more efficiently while lowering your risk of heart disease. The exercise also helps manage cholesterol levels, reducing dangerous plaque buildup. Cardio is also linked to lower incidence of diabetes and certain types of cancer. It releases endorphins to make you feel good, helps preserve cognitive function as you age and could even extend your life.
Nina K. is a Los Angeles-based journalist who has been published by USAToday.com, Fitday.com, Healthy Living Magazine, Organic Authority and numerous other print and web publications. She has a philosophy degree from the University of Colorado and a journalism certificate from UCLA.