Hormones cause women to gain fat on the thighs, according to Patrick J. Bird, dean of the College of Health and Human Performance at the University of Florida, writing for “Scientific American.” Combined with poorly toned muscles, this results in flabby thighs. A workout routine of cardiovascular exercise to burn fat and strength-training exercises using your body weight, free weights and resistance equipment will help you get sleek, toned thighs. Do this workout a minimum of three times a week.