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Is there any need to run or jog if I walk 10 miles almost everyday?(r/Fitness)
Your body adjusts differently in response to training at different heart rates. Different heart rate zones correspond to different types of training, including recovery, general aerobic, lactate threshold, VO2 max workouts, etc.
Training at a heart rate in the “aerobic zone” has plenty of cardiovascular benefits, including increasing the number and size of mitochondria (producing more energy aerobically), increasing aerobic enzyme capacity (improving efficiency of mitochondria), and increasing the number of capillaries surrounding your muscle fibers (delivering oxygen more efficiently where it’s needed).
Both running and walking (and cycling and dancing and rowing and so on, basically any prolonged activity that increases your heart rate) can develop cardio, but unless you are huffing and puffing on a power-walk, it is more difficult to reach this “aerobic zone” via walking than with running. Yes, you are still making cardiovascular benefits in the “recovery zone,” but they are not quite as large as the benefits in the “aerobic zone.”
How would you know you’re improving your cardio? When under the same environment and weather/temperature conditions, your running pace gets faster at the same heart rate or heart rate zone. This has been proven over and over again with the millions of runners in the world. Again, the same goes for walking, but don’t expect to get the same benefits in the same amount of time if you’re only going at a leisurely pace inside the “recovery zone,” which is what I’m assuming OP is doing on his commute.
Sources: the website and Pfitzinger’s “Advanced Marathoning” book
EDIT: Added extra stuff + formatting.