You may marvel at the speeds that elite distance runners are able to maintain over the course of a 10k or marathon race, along with the fact that they seem to have minimal body fat. Although you will probably never be able to achieve their race times, you may wonder if losing a few pounds will help you run faster times. Many factors play into the magnitude of speed gain with weight loss --- in particular the amount of fat lost, how much weight you can safely lose, incorporation of interval training, and how weight loss affects your training.
Fat Loss
Not all pounds are created equally. Losing a pound of excess body fat will likely make running feel easier and improve your aerobic capacity since fat is essentially inert --- you must carry the weight with you while running. Conversely, losing a pound of muscle will reduce your overall metabolic rate and may reduce your strength, since this is the mass that powers your run. Therefore, to maximize your running speed gain, you should aim to make the majority of your weight loss from fat, not muscle.
Amount of Weight You Have To Lose
The amount of weight you can lose without compromising your health will dictate how much faster you can run. A body mass index --- or weight in kilograms divided by the square of your height in meters --- between 18.5 and 24 is considered a healthy range. You will probably see the biggest improvement in running speed with weight loss if you are above this range --- provided you are eating healthfully, training consistently, and losing primarily fat mass. If you are already within the healthy body mass index range, your improvement in running speed will likely be much less, and going below a minimal essential level of body fat --- 5 percent for most men and 12 percent for most women --- will compromise overall health and eventually your running.
Types of Workouts
If you run the same moderate-intensity pace every workout, your running performance --- and possibly your weight loss -- will eventually plateau. Your body becomes more efficient at that moderate pace, meaning you will eventually burn fewer calories running the same pace. Incorporating interval training --- short bursts of fast running interspersed with slow jogging or walking --- may help you burn more fat than continuous aerobic exercise, according to a 2008 study in the "International Journal of Obesity." Interval training improves running speed even without weight loss; combined with the additional fat loss, interval training could make an even greater impact on your running speed.
Quality of Training
Losing weight requires that you consume fewer calories than you expend. If you drastically reduce your calorie intake however, you will lack the energy to train optimally. Reducing your calorie intake by no more than 200 to 300 calories per day will allow you to maintain your energy to run and lose weight gradually at the same time. When you reach your target weight, you will be faster not only due to fat loss, but because you were able to run quality workouts in the process.
References
- "International Journal of Obesity"; The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women; Trapp et al, January 2008
- "Science and Practice of Strength Training, 2nd Edition", Vladimir M. Zatsiorsky and William J. Kraemer; 2006
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