Large thigh muscles are a result of two factors: your predominant muscle fibre type and the amount of resistance applied when exercising. More muscular body types, known as mesomorphs, respond quickly to resistance exercise, and thus develop big thigh muscles. To get rid of those big muscles, it is important to do exercises that lengthen and work the muscles without adding resistance.
Lunge your way to slimmer thighs. Find a space where you can perform 15 to 20 walking lunges. From a standing position, hold your hands at your hips and take a long stride forward with your right leg, bringing your knee to a 90-degree angle over the heel while lowering your left leg in the process. Draw your left leg up to standing and then repeat, alternating legs across the floor. Complete two sets. Do these just twice a week with at least 48 hours between conditioning sessions.
Execute body-weight squats. Stand up straight, then lower your hips, bringing your knees near a 90-degree angle. Pause and return to standing. Imagine tapping your backside on a chair as you complete 15 to 20 repetitions. Rest 30 seconds to a minute and then repeat for a total of two sets. You'll be using your thigh muscles in an endurance-enhancing way, which will focus on slow-twitch muscle fibres rather than the fast-twitch, which get bulky with heavy weights. Do squats on the same two days you do lunges.
Perform cardiovascular exercise three to five times a week. Shoot for five. Increase your number of days by gradually adding one a week until you reach five days a week. Increase your time per session if you're already exercising as many days a week as you can. If you're currently doing 20 minutes, increase to 22 and then to 25 in consecutive weeks. Increase until you're doing 60 minutes at least once or twice a week if your schedule will allow it. Choose exercise modes that minimise workload to your lower body. For instance, keep the resistance down on your spinning bike and keep your risers low in a step aerobics class. Walking, jogging and swimming are ideal cardio exercises as they promote elongated muscles and minimum additional resistance.
Do Pilates. Promoting development of longer, leaner muscles, Pilates is an effective conditioning exercise. Find a mat-work class or video. Exercises specific to the lower body include side leg series, scissors and leg circles (see Resources). You will primarily use your body weight against gravity as resistance. While you'll be losing muscle mass, you'll be retaining some tone in your thighs.
Be patient. It may seem like the muscle mass you want to lose came on overnight, but it will take a little time to take it off. Eat for the body you want to have, not the one you have now. That might mean cutting back on some calories. Safe and permanent weight loss and gain is slow and steady. For specific nutrition information, contact a registered dietitian.