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The fundamental determinant of body weight is caloric balance—the number of calories you consume through eating and drinking minus the number of calories you expend through physical activity, digestion of food, and all of your other daily activities. You use calories all the time. Every time you contract a muscle, either voluntarily or involuntarily, you use calories. Your other organs—heart, kidneys, liver, pancreas, brain, and so on—also use calories to carry out their varied functions. Hippocrates wrote that “eating alone will not keep a man well; he must also take exercise.” I’m not sure if Hippocrates ran, but if he did, he would have discovered that running is the most effective exercise to keep a man (or a woman) well, especially when it comes to losing weight and keeping it off. There are three major reasons why:
1. Running creates a great need for energy.
When you run, you lower your carbohydrate fuel tank, you cause slight microscopic tears in your muscle fibers from the strong muscle contractions, and you increase body temperature. As soon as you stop running, your body naturally wants to return these things to their pre-exercise state. So, following a workout, your body rushes to replenish glycogen, repair the microscopic muscle tears, lower body temperature, and synthesize new structural and functional proteins as your body adapts. Your body requires energy (calories) to accomplish all of these tasks. If you don’t run or do any other exercise, there is never a drain on muscle glycogen, nor any muscle tissue to repair or build, nor any reason to make new proteins, so any calories you consume that are greater than your metabolic needs are stored as fat. If you don’t want your calories to be stored as fat, you need to exercise. Research shows that the amount people run is closely linked to how much weight they lose, partly because of the large caloric deficit that running creates. And the converse is also true: The more runners decrease the amount of running they do, the more weight they put on. One of these studies is from the National Runners’ and Walkers’ Health Studies, the world’s largest and longest-running series of studies on the health benefits of running and walking. Scientists divided 41,582 female runners into groups based on their age and the number of miles they ran per week. Compared with those who ran less than 10 miles per week, those who averaged over 40 miles per week had a 10 percent lower body mass index (your weight divided by your squared height; the most common value used to determine obesity), 8 percent lower waist circumference, 7 percent lower hip circumference, and 4 percent lower chest circumference. In every age group, the greater the number of miles run per week, the lower the body mass index and chest, waist, and hip circumferences.
In another study from the National Runners’ and Walkers’ Health Studies, the researchers charted the running habits and body weight of 270 men and 146 women who started running, 3,973 men and 1,444 women who quit running, and 420 men and 153 women who remained sedentary during 7.5 years. They found that body weight and abdominal fat decreased in the people who started running and increased in the people who stopped running and in those who remained sedentary, with the changes proportional to the change in the amount they ran. In other words, the more the previously sedentary people ran, the greater the decrease in body weight and abdominal fat. Conversely, the more the runners reduced the amount they ran, the more their body weight and abdominal fat increased. Running is a great way to burn intra-abdominal fat. Any runner who has ever been injured and can’t run knows how easy and quick it is to put on weight. Running is one of the best ways to keep the weight off and become a leaner and fitter you.
2. Running uses many muscles.
All the muscles in your legs (quadriceps, hamstrings, hip flexors, abductors, adductors, glutes, calves, and the muscles in the front of your shin) are used at different points in the running stride. You even use your abdominal muscles and the muscles in your shoulders a lot when you swing your arms back and forth as you run. The more muscles you use, the more oxygen you use, and the more oxygen you use, the more calories you burn.
3. Running is weight bearing, which provides stress to the skeleton.
Every time your foot lands on the ground, your leg absorbs two to three times your body weight. Multiply that number by the number of steps you take on an average run, and multiply that by how many times you run each week, and you can see how much stress your legs have to deal with, especially if you’re overweight. Because it threatens your body’s survival to have all that stress on it, your body will do what it needs to do—shed weight—to alleviate the stress and assuage the threat to protect itself. Can you burn calories, sculpt your butt and legs, and lose weight in ways other than running? Of course you can. But running burns and sculpts more. And that matters. Other forms of exercise burn so few calories that it’s too easy to get the calories right back after completing a workout—the 30 minutes of walking or cycling it takes to burn 200 calories can be negated in just a few seconds with a glass of Gatorade and a handful of pretzels. Running, with its huge calorie burn, is your best chance to create an environment for fast weight loss and sculpt your lower body. The muscular forces generated when you run are nothing short of extraordinary. Because other activities don’t use as many muscles and are not as weight bearing as running, you don’t lose weight as quickly. These three principles are a central theme throughout this book and will guide you throughout your running and weight-loss journey.
After you determine determine the best time of day to run, all you need is a good pair of running shoes and activewear. After you run, you need to refuel, but be careful not to replace all the calories you burned while running.