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 your leg muscles.
Combining cardiovascular exercise with targeted thigh resistance training will change the appearance of your legs.
Read more: A Beginner Leg Workout Routine
Exercises for Your Thighs
Choose moderately intense to challenging cardio exercises to do every day. Perform multi- and single-joint exercises at least two to three days a week on nonconsecutive days.
1. Exercise Aerobically Every Day
Perform cardiovascular exercise at a moderately-intense rate for 150 to 300 minutes per week for moderate fat loss, or 75 to 150 minutes a week vigorously for significant fat loss, according to the Physical Activity Guidelines for Americans.
2. Choose a Challenging Activity
Choose any activity that you enjoy, but it should be challenging to burn more calories and fat. For example, a 155-pound person can burn 298 calories if she walks for one hour at 3.5 mph, according to Harvard Health Publishing. The same person can burn 596 calories an hour by jogging at 5.0 mph. Jogging will lead to greater results over walking.
3. Interval Train for Calorie Burn
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.
4. Multi-Joint Exercises
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.
5. Single-Joint Exercises
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.
Read more: 10-Minute Leg-Sculpting Workout
Choose challenging cardio over easy cardio exercise for decreasing body fat. Vary the cardio workouts you perform to avoid a fitness/weight-loss plateau. Change the thigh exercises you perform every four to six weeks. Use enough resistance that it is hard to finish eight to 12 repetitions per exercise. See a physician before beginning any exercise program. Combine a healthy, balanced diet with your exercise program for better results to your thighs.
Do not start with the maximum amounts of recommended exercise. Stop exercising if you feel pain, dizziness, lightheadedness or nausea. Do not perform thigh exercises every day hoping for faster results. Do not drastically cut your calories hoping for faster fat loss.