Carrying less weight means you need less force to accelerate that weight, (force = mass x acceleration) Newton's second law. Less force over a distance is less work (work = force x distance). As a runner you are always accelerating and therefore applying force as you speed up/slow down, push through the friction of the air, push up against gravity, and overcome frictional losses of your foot landing on the ground. A smaller mass to accelerate means less force you must apply and less force means less work.
The energy consumption of humans running is approximately 1 kcal/kg/km, regardless of speed. Running 1 kilometer for a 90.7 kilogram (200lbs) person will consume 90.7 kcal of energy, however a 77.1 kilogram (170 lbs) person will consume roughly 77.1 kcal of energy. This means less weight (mass) also yields a more efficient runner, requiring less energy to travel the same distance.
Having less body mass also means you generate less heat since you perform less work, you can also dissipate heat easier. Heat is generated by muscle as it performs work. Maintaining lower heat allows you to perform at higher levels for longer periods of time.
Some running sources say that you can cut 2 sec/mile from your pace for each pound that you lose. Losing 10 lbs can cut your marathon time by nearly nine minutes, or a 5k time by one minute. Of course there are extremes where you will no longer benefit from this weight loss as it begins to cut into your muscle mass.
|Sample Results of Metabolic Test for 27 Year Old Male|
Your baseline metabolism (also called: basal metabolic rate: BMR, or resting metabolic rate: RMR) is the amount of energy, in the form of calories, that your body consumes/transforms in a day if you were just to sit around.
You also have two other sources of energy consumption on top of your baseline metabolism: daily activity such as going to the grocery or walking around the house, and your exercise. The sum of all of these is your daily metabolic burn or consumption, measuring in calories.
In order to maintain your present weight, you must eat as many calories as your body burns. To lose weight you must eat less than your body burns. This can be done by burning more, eating less, or both. I would recommend not starving yourself or changing your eating drastically as it will have detrimental effects on your baseline metabolism and you will not lose weight. Instead, you should target to eat approximately your baseline metabolism every day. This will mean that you are running a deficit of the calories you consume through activity and exercise which will cause you to burn your fat reserves and lose weight in a safe and healthy way, and at a reasonable rate (about 1-2 lbs per week).
You can determine your baseline metabolism by taking a test administered at a clinic or fitness center. You may need to search for local doctors offices or ask your doctor where you can take this test. I was able to get mine tested through a program at work. The test takes 10 minutes. You breathe into a tube as you would normally breathe, while resting in a chair. They also put a clamp on your nose to make sure all of your exhaled breath is analyzed by the machine to determine your resting metabolic rate. It works by using indirect calorimetry, burning 1 calorie requires 208.06 milliliters of oxygen. This relationship means caloric burn rate and oxygen intake are related and interchangeable. The machine measures the volume of air exhaled and the concentrations of oxygen in the exhaled and inhaled air to determine how much oxygen was consumed and converted.
The result of this test will help you plan you diet in a way that helps you lose weight effectively and safely.
Korr makes metabolic testing equipment