Riding an exercise bike works your thighs, so it seems reasonable that it should reduce the fat on your thighs. But unfortunately that's not exactly how exercise works. The good news is that riding an exercise bike can help you lose weight overall and tone your thighs, giving you the great looking legs you're looking for.
Reducing Thigh Fat
Using an exercise bike won't specifically reduce your thigh fat -- this is because you can't simply lose fat in a desired part of your body. When you lose fat it will happen throughout your body. So no exercise is specifically good for losing thigh fat. But cardiovascular activities like riding an exercise bike are good for losing fat in general, so you can expect to reduce your thigh fat -- along with your overall body fat -- with an exercise bike.
Calories Burned
The number of calories you burn with an exercise bike will depend on the intensity of your workout as well as your weight. The intensity of a stationary bike is measured in watts -- the amount of energy you produce which is displayed on most stationary bikes -- as opposed to speed. If you weigh 130 pounds, an hour of very light cycling at an intensity of 50 watts will burn just 118 calories, but if you weigh 200 pounds it will burn 182 calories. An hour of very vigorous cycling, producing 250 watts, will burn 679 calories for a 130-pound individual or 1,047 calories for a 200-pound person.
Weight Loss
If you burn more calories than you consume, your body will burn fat as a source of energy. You need to burn 3,500 calories more than you eat to lose 1 pound of fat. So if you weigh 150 pounds and cycle vigorously at a 250-watt intensity, burning 1,047 calories an hour, you would have to exercise for approximately three hours and 20 minutes to see 1 pound of fat lost. So if you ride an exercise bike at that pace for an hour and seven minutes, six days a week you could expect to lose approximately 2 pounds per week.
Toning Thighs
While riding an exercise bike won't spot reduce fat on your thighs, it will help tone your thigh muscles. Because cycling works the legs, you can expect regularly riding an exercise bike to contribute to stronger, more toned legs, specifically including the thighs as well as your hips and rear end.