You may swear you feel your thighs shrinking with every mile on the treadmill, but the truth is that exercising doesn't directly affect fat deposits. There's no such thing as spot reduction, but running does play a role in overall fat loss by burning calories. Reducing total fat will shrink your body proportionately for smaller thighs. Running also tones leg, thighs and glutes for a shapelier figure. Ultimately, what you eat will have even more effect on body size than exercise, so watch your diet to see results.
Running and Calories
As one of the top calorie-torching exercises out there, running helps you create the energy deficit required for weight loss. If you weigh 155 pounds, a treadmill jog at 5.2 mph burns about 335 calories in 30 minutes. At a pace of 6.7 mph you'll incinerate more than 400 calories in 30 minutes, and at 10 mph you'll blast a whopping 600 calories in the same time frame. To put this in perspective, a pound of fat equals 3,500 calories.
Running engages quadriceps on the front of your thighs and the hamstrings in the back, as well as glutes, hip flexors and core. These muscles will get stronger and better toned on the treadmill, but running still doesn't replace strength-training exercises such as lifting weights or performing squats and lunges. Strength training is important for muscle building, posture and overall health, and it can also make you a better runner -- provided you work all major muscles. If you work your quads but not your hamstrings, for example, you create an imbalanced gait that can lead to injury when you run.
Building a Routine
If you're new to the joys of running, take it easy at first. Start by walking, and when you feel comfortable, set the treadmill to around 5 mph for a brief jog. Alternate jogging and walking until you can jog straight through without becoming breathless, and eventually incorporate faster speeds. You'll probably feel sore after your workouts, even at low speeds, until your muscles adapt. Warm up and cool down every time you run; a brisk five- to 10-minute walk will do it.
Other Treadmill Benefits
Vanity is by no means the only reason to hit the treadmill. Running increases your aerobic fitness by forcing your heart and lungs to work hard, resulting in greater efficiency over time. The activity also releases stress, easing anxiety and possibly even depression. As a runner, you have a lower risk of high blood pressure, high cholesterol and heart disease than a non-exerciser. Your mind will stay clearer as you age, and your immune system may be more effective in warding off colds and flus.
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