Dear Alice,

I have a question about walking for weight loss. My walking buddy believes the theory of walking distance is what helps you lose weight best versus my theory that it is the speed at which you walk that matters. So, could you help me figure this one out? Which matters most in ultimate weight loss: speed or distance?

Speed walker

Dear Speed walker,

If Speed and Distance were competing in a race for the #1 weight-loss title, Distance would come out slightly ahead. Specifically, duration matters slightly more than intensity, though intensity is also an important factor. Here's how duration wins the fat-burning game: Exercise results in weight-loss when you either, a) expend more calories than you take in, or b) burn fat during your workout. Or both.

The body gets its energy from three primary sources: carbohydrates, fat, and protein. For the first 20-30 minutes of exercise that gets your heart rate up, carbohydrates are usually the primary source of muscular energy. Carbs are ideal because they are quick and easy fuel, requiring the least amount of oxygen to burn. If you were to suddenly get up from your computer and sprint for one minute, you would be burning carbs. However, once exercise time exceeds 30 minutes, there is an increased reliance on fat stores for energy because you begin to run out of the easy stuff.

Here's where intensity comes in. At low to moderate intensities (50—70 percent of your maximum heart rate), fat is the preferred fuel for muscles because you are burning calories at a slower rate and are thus not requiring the "quick" energy found in carbs. At higher intensities (70 percent or more of your max heart rate), the accumulation of lactic acid in the muscles inhibits fat utilization and carbohydrates become the primary source of energy. Therefore, low to moderate intensity exercise is ideal for maximum fat burning, especially if you have the time to devote to a longer exercise regimen (over 30 minutes). An individual's personal fitness level also determines their ability to burn fat. Higher fitness level is correlated with a greater ability to burn fat at all intensity levels because your body uses oxygen more efficiently when you're in good shape.

If you aren't sure about your max heart rate, an often followed guideline involves having a conversation while you exercise. If you and your walking pal can hold a conversation as you walk, you are likely doing low to moderate intensity working out. But if you are too out of breath to talk comfortably, you have probably crept up into the high-intensity realm. Thus, your calorie burning will go up, while your fat burning will go down.

Generally, regardless of which method burns more body fat, low-intensity exercise may be more appropriate for inclusion in an exercise program because it is better tolerated and will therefore result in more adherence to the program. It is also less likely to result in injury. However, a benefit of walking at a faster pace is that it helps improve cardiovascular function and fitness level. In time, a person who trains at higher levels of intensity can slowly increase his or her exercise time, building up endurance. A benefit of walking at a slower pace is that it allows a person to be in motion for a longer duration before becoming tired, which helps to build up endurance. In time, a person can slowly increase the intensity (speed up his or her walking), improving his or her level of fitness. Improvements in fitness occur by increasing the body's use of oxygen. Whether the intensity is high and duration is short, or the intensity is low and duration is long, relatively the same amount of oxygen is utilized and the same number of calories is expended.

What really counts is to be consistent in any activity you choose to do. Mixing it up — some days going for intensity with shorter, faster walks, and some days going for endurance with longer, slower walks — can keep you on your toes (pun intended). It can also make your exercise routine more interesting, fit into any schedule, and keep you and your buddy satisfied and happy.


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