Both cycling and running has similar cardio benefits.
Both cycling and running can help you tone and slim down your legs. However, it is important to note that you can't spot reduce fat in your legs. In order to slim your legs, you must reduce your overall body fat. Both running and cycling are effective for cardio and burning fat. When combined with healthy eating, your legs will slim down and gain some muscle definition.
Creating a Calorie Deficit
Between your cardio routine and your diet, you need to burn more calories than you consume to lose weight and burn fat. The Centers for Disease Control and Prevention recommends losing between 1 to 2 pounds per week for long-term success. To achieve this, you need to create a daily calorie deficit between 500 to 1,000 calories, as a pound of weight is equivalent to 3,500 calories. By replacing high-calorie foods such as condiments, fast food and soda with lean protein such as chicken breast, vegetables and fruits, you can reduce your calorie intake without consuming less food.
Burning Calories Quicker
Running generally burns more calories than cycling. Jessica Matthews of the American Council on Exercise states that using a treadmill is the most effective choice of equipment for burning calories -- beating out others, such as the stationary bike. According to the American College of Sports Medicine, an individual who weighs 150 pounds will burn a 1,000 calories in an hour when running at a seven-minute mile pace. The same individual will burn 850 calories when cycling at a pace of 16 to 19 miles per hour.
An Exercise Program
To burn fat and slim your legs effectively, perform vigorous cardiovascular workouts, such as high-intensity internal training (HIIT). This exercise helps you burn calories and fat, both during and several hours after the workout is complete. Start this exercise with a five-minute warm-up on a stationary bike or treadmill. Rev up the intensity as high as you can for one minute, then slow down to a moderate pace for two minutes. Continue these intervals for 20 to 30 minutes, depending on your level of fitness.
Choosing What Suits You
You are more likely to burn the most calories performing an exercise you enjoy. For instance, if you enjoy cycling more than you do running, you are more likely to exercise for a longer duration or higher intensity. You should also consider your health when selecting a workout to slim your legs. Those with joint or bone issues such as osteoarthritis may be better off cycling due to its low-impact nature. High-impact workouts such as running are more ideal for athletes or those with strong bones.