You can't spot reduce fat from a specific area of your body. You also can't convert fat into muscle. What you can do is firm up your flabby thighs by reducing the amount of body fat from your whole body -- which will include the fat on your thighs -- and toning the leg muscles. Combining cardiovascular exercise with targeted thigh resistance training will change the appearance of your legs.
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Perform cardiovascular exercise three to five days per week for moderate fat loss, or five to seven days per week for significant fat loss, according to the American College of Sports Medicine. Exercise for 30 to 60 minutes each session at a moderate to high intensity for the best results.
Choose any activity that you enjoy, but it should be challenging to burn more calories and fat. For example, a 160-pound person can burn 277 calories if she walks for one hour at 3.5 mph, according to the MayoClinic.com. The same person can burn 584 calories an hour by jogging at 5.0 mph. Jogging will lead to greater results over walking.
Interval-train. Incorporate high-intensity interval training into your workout for greater fat loss. For example, you can alternate walking and running if you cannot run for an extended period of time. Start with a five minute walking warm up. Run fast for 30 to 90 seconds, followed by one to three minutes of brisk walking. Alternate walking and running for the duration of your workout.
Train your legs two to three times per week on non-consecutive days. Do one to three sets of 8 to 12 repetitions per exercise. Choose two to four multi-joint exercises for your workout. You can do squats, lunges, step-ups or any of their variations. These exercises work the glutes, quadriceps and hamstrings muscles in your lower body. Hold a set of dumbbells while executing each exercise. To perform a squat, stand with your feet shoulder-width apart, bend at the hips and knees, lowering your body and standing back up. Go right into lunges by standing with your feet hip-width apart and stepping forward with one foot. Lower your body by bending the hips and knees and press back up to the start position. Alternate your legs for toning on both thighs. Perform step-ups by using a bench and stepping up on top of it and lowering yourself with the same leg. Perform repetitions on both legs for balanced thigh toning.
Perform two to four single-joint exercises in addition to your multi-joint exercises if you want to target your thighs more. Leg extensions, leg curls or any variations are appropriate. Perform leg extensions in a seated position to tone the fronts of your thighs by straightening and bending the knees. Perform a lying leg curl by lying on your stomach. You raise and lower a weight by bending and straightening the knees to tone the backs of your thighs.