According to 12 Minute Athlete, it's common to experience an increase in the size of your thighs at a certain point in a new workout routine. Actually, this phenomenon is not exclusive to your thighs, but it's just more noticeable within that area. In most instances this issue will self correct as you progress through the routine; if not, there are some steps you can take.
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The Science Behind Your Dilemma
From an aesthetic point of view, exercises can be designed to help you lose weight or build muscle, and in many cases the workout will accomplish both. According to Dr. Mustafa Gil, M.D., an assistant professor of Physiology at Ataturk University in Erzurum, Turkey, when you engage in high-intensity workouts, you recruit low-endurance muscle fibers known as fast twitch, or glycolytic, fibers. These fibers are consequently broken down and as they rebuild they get larger.
The Second Half of the Equation
Muscle hypertrophy -- the enlargement of muscle fibers -- is not the only culprit here. When you first begin your workout you will experience significant results in the area of weight loss. As you progress, your body will adjust to the intensity of the exercise and you will experience a plateau in which you will see a noticeable decline in the rate at which you are losing weight. This decline in fat loss, coupled with muscle hypertrophy, equals bigger thighs.
Lower Your Workout Intensity to Slow Hypertrophy
Although hypertrophied thighs can be a little scary, especially for women, it's not necessarily a bad thing. According to Share Care, increasing lean muscle mass assists your body in burning calories more efficiently; however, if you want to retard the growth of your thighs, lower the intensity of your workouts. You can do this by reducing the weight resistance, and eliminating explosive movements and rapid recovery times between sets.
Adjust Diet and Cardio
To ensure you are able to maintain a safe and steady weight-loss rate, modify your diet by lowering it by 300 to 375 calories per day. Insert some random variations into your workout so your body cannot adjust to it. You can adjust the weight, reps, recovery time and more. You want to keep your body guessing so it can't adapt. This will allow you to maintain a steady rate of weight loss. When adjusting your workout or changing your nutritional diet, be sure to consult your physician to ensure you are not placing yourself at risk.