It sure is a bit difficult to say. Basically, this depends on a few factors: age, weight and space to walk. You can burn about 150 calories per hour, according to the hypothesis. If you want real exercise, you'll get a variable speed unit that lets you set your own pace. Just use the lawn mower to move the grass quickly. Many self-propelled lawn mowers can go up to 4 miles per hour. This is faster than walking in the park.