We have a natural tendency to walk slow and run fast because it is more efficient to walk slow and more efficient to run fast. As we speed up, walking becomes less efficient and running becomes more efficient. The literature I have seen on this subject suggests that the crossover point (where walking and running are equally efficient) is somewhere between 15 minute-per-mile pace and 12 minute-per-mile pace--depending on the walking and running styles used. My own tests indicate my personal crossover point is somewhere in that range.
Several conclusions can be reached based on the variations in efficiency of walking and running at different speeds.
- Anyone who tells you that the calories burned by a 150-pound man going one mile is the same no matter whether he is walking or running, or going fast or slow, is simply not recognizing the impact of efficiency on going that mile. I'm sure that person would agree that the calories burned by a 150-pound man walking one mile is less than the calories burned by a 150-pound man crawling on his stomach for one mile, or a man swimming for one mile--and that the differences are due mainly to the differences in efficiencies of movement technique. (NOTE: Most calorie calculators for walkers and runners seem to ignore the efficiency factor, and the ones that are based on actual measurements do not overlap. In the latter case, all walking measurements are based on 12 minute-per-mile pace or slower, and all running measurements are based on 12 minute-per-mile pace or faster. If you graph their calorie counts however, you will see that the slopes of the lines for walking and running are different at 12 minute pace.)
- The difference between the world-best marathon time for a male runner (2:04:26 in Aug 2008) and the marathon-equivalent time for the world-record 50K men's race walk (3:00:47 in Aug 2008 based on a 3:34:15 50K) is due mainly to the efficiency gained by the runner in lifting off the ground between each step. (In the flight phase, a runner encounters almost no resistance and adds significantly to the step length. Because speed is a function of step length and step rate--with the latter being about the same for runners and walkers, the runner finishes the marathon 56 minutes ahead of the race walker primarily because of his increased step length. Also note that the race walker could probably have completed the marathon slightly faster if he did not have to still go the extra 5 miles to reach 50 kilometers.)
- A runner does not necessarily get a better workout running for one hour than a walker gets walking for one hour--and vice versa. It all depends on the effort expended, and walkers can expend energy just as quickly as runners. (The body has no way of knowing how fast you travel or how far you go.)
- A runner passing a walker in a race might be working harder, working at the same level, or working less than the walker depending on their speeds and the efficiency of their styles.
Let me give you two simple tests you can perform to confirm the variations in efficiency for walking and running at different speeds. In both tests, make sure you maintain contact with the "ground" while walking, and lift off the "ground" between each step while running.
- Test 1 (on a paved surface) - Part 1: As a walker, ask someone to run along side of you while you walk. They must not get behind you or ahead of you. Then casually walk at about a 1-mile-per-hour pace (60 minutes per mile). I guarantee you they will soon complain about the extra energy required to run at that speed. Part 2: As a runner, ask someone who runs to walk along side of you while you run. They must clearly walk (maintaining constant contact with the ground), and must not get behind you or ahead of you. Then you run at about a 6-mile-per-hour pace (10 minutes per mile). Again, I guarantee they will soon complain about the extra energy required to walk at that speed.
- Test 2 (on a treadmill) - Part 1: Get on a treadmill and bring it up to a 1-mile-per-hour pace while you walk. Monitor your heart rate until it stabilizes and note the pulse rate. Then, at the same speed, switch to running. Your pulse rate will begin to rise as you expend extra effort. Part 2: After your heart rate recovers, get on the treadmill and bring it up to a 6-mile-per-hour pace while you run. Monitor your heart rate until it stabilizes and note the pulse rate. Then, at the same speed, switch to walking. Your pulse rate will begin to rise as you expend extra effort.