You may hope to burn off a pound in a day, but an attempt to burn 3,500 calories all at once on a regular basis is not healthy. Depending on your size and speed, it could take anywhere from 3 to 10 hours, or 180 to 600 minutes, on the treadmill to burn all those calories. A marathon session like this isn't good for your body, and can be downright dangerous. Always consult your doctor before beginning any new exercise regimen.
How Long Do You Go
A 155-pound person burns about 596 calories in 60 minutes going 5 mph on the treadmill. At this rate, it'll take almost six hours to burn 3,500 calories. Even if you weigh more -- say 185 pounds -- and go at a faster pace of 6 mph, it will still take almost four hours to total 3,500 calories burned. A 125-pound person will need to go six hours at the 6 mph pace. A 300-pound person burns calories at a faster rate, but he is unlikely to be able to keep up a jogging or running pace for a sustained period of time. If this larger person goes 3 mph on the treadmill, he burns about 594 calories per hour -- so it will still take almost six hours total to reach the desired 3,500-calorie burn. If the 155-pound or 185-pound people walk at 3.5 mph, it'll take between nine and a half and 11 hours to finish the goal.
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A Sustainable Approach
You are better off breaking up the workout over several days to burn the 3,500 calories. The Centers for Disease Control and Prevention recommend a minimum of 30 minutes of moderate-intensity cardio per day, five days per week. Exercising more affords greater benefits, including a higher calorie burn, but speak with your health care provider about how much she recommends you aim for each day. A weekly weight loss of one to two pounds is said to be safe and sustainable for most, and usually comes about with a combination of exercise and dietary measures.