In addition to improving cardiovascular conditioning, exercise can give you a fit, toned appearance. Some girls may think, however, that they are overdoing their exercise regimes when they develop large, muscular looking legs. Girls cannot become overly muscular from working out due to differences in the types of fibers that make up their muscles and lack of testosterone. If the size of your legs becomes larger after you have been exercising for a couple of months, this difference is probably because you have developed a layer of muscle over a layer of fat. Follow sensible diet and weight guidelines to reduce body fat while you maintain your exercise routine and you'll notice slimmer, more defined legs.
Weigh yourself. Look up the figure you got in growth tables for your age. Find your age on the bottom or horizontal axis of the chart. Locate the 25th percentile on the right or vertical axis of the chart and jot down the number at the intersection of these two points. This figure would be 112 pounds for a 17 year old girl, for example. This is the low end of the average range. Find the intersection between your age and the 75th percentile and jot down this number, which is the high end of the average range. This figure would be 140 pounds for a 17 year old girl, for example. If you are 17 and weigh 118 pounds, you are of average weight because the range for 17 year old girls is between 112 and 140 pounds.
Calculate your body mass index, which is the proportion of body fat you have relative to your lean tissue. Calculate your height in inches. If you are 5 foot 5 inches tall, for example, you are 65 inches. Square your height in inches by multiplying it by itself. If you are 65 inches, for example, your height squared would be 4,225 inches. Divide your weight in pounds by your squared height in inches. If you are a 5 foot 5 inch girl who weighs 118 pounds, for example, the answer would be .03. Multiple this figure by 703 to get your BMI, which is 21.09 in this example.
Use a growth chart to compare your BMI to other girls your age. Find your age on the bottom of the chart and align it with 25th percentile. Jot down this number as it is the low range of average, in the previous example it's 19. Find the figure at the 75th percentile, which is the highest number in the average range, in this case 23.25. A 17 year old girl, for example with a BMI of 21 is within the normal range as a BMI of between 19 to 23.25 is considered normal.
Take a reality check. If you think your legs are too muscular and your BMI and weight are well within the average range, perhaps you are comparing yourself to other body types that are taller, underweight or built differently than you. If, on the other hand, your BMI is above the 75th percentile, you may want to consider losing some weight as you continue working out to tone your muscles.
Lose the Fat
Cut down on your carbohydrate intake to reduce your excess body fat, according to professor of nutrition at the University of Alabama, Barbara Gower. Choose fruits and vegetables over processed foods. Girls should keep their total fat intake between 25 to 35 percent of their total calories, according to the Center for Disease Control and Prevention. Choose polyunsaturated and monounsaturated fatty acids, which include fish, nuts and vegetable oils over saturated fats, such as that found in potato chips.
Burn some excess calories. Choose aerobic activities if you are trying to lose weight, such as brisk walking, bicycling, jogging or dancing. Aim for at least 60 minutes a day of moderate-intensity exercise. Exercise at a vigorous-intensity level at least 3 days per week according to the CDC fitness guidelines for children.
Aim for a reduction in net calories of 3,500 per pound of weight loss desired. A girl who weighs 118 pounds, for example, would need to burn 875 extra calories a week through a combination of exercise and diet restriction to lose a pound a month. She might burn 3,000 extra calories by doing 60 minutes of aerobics twice a week, for example, and cut down her caloric intake by 500 calories per month.
Make small changes each day for big overall results. Try a combination of techniques, such as cutting down portion sizes, asking yourself if you are full when you are eating, trying not to eat when you are distracted and chewing slowly, according to the website Seventeen.