Look again at the results of the Syracuse University study. Men burned more calories than women during both segments because they weigh more. Moving a body that weighs more requires more energy; hence, it burns more calories. The difference between running and walking is similar to the difference in weight, physicswise. Walking requires far less movement than running does.
Consider what Runner's World writer Amby Burfoot points out. When we walk, we maintain a level center of gravity and we propel ourselves by sticking our legs out one at a time and bending slightly at the knee as they carry that center of balance forward. Running, on the other hand, is far more complex and involves much more effort than walking. When a human runs, he or she achieves forward movement by essentially hopping from one foot to the other. Each hop requires the entire bulk of the person to be lifted from the ground and pushed forward. This distinction in motion explains why running burns more calories than walking -- it just requires more energy [source: Burfoot].
So how many calories does running burn? Again, weight is a major factor. So, too, is the distance the person runs and the duration. The Mayo Clinic uses the general rule of thumb that a runner can calculate the approximate amount of calories he or she burns during a run simply by multiplying one's weight in pounds by 0.75. For a 160-pound person (73 kilograms), running a mile burns 120 calories. Remember that duration and distance are also factors as well. If that same person runs eight miles (12.8 kilometers) in one hour (or eight miles per hour), he or she will burn approximately 986 calories [source: Mayo Clinic].
For more information on running and energy, see the links on the next page.