Treadmills are the most popular cardiovascular machines. They are very easy to use, if you can walk or run, you can use a treadmill. They are also one of the best ways to burn fat. Studies have shown that running on a treadmill burns fat more effectively than most cardio exercises. For those concerned with low bone density, running or walking are good load-bearing exercises that have been shown to increase bone density. There are many types of treadmills, fold-up models, models designed for walkers, heavy-duty designs for runners, even ones that can monitor your heart rate and adjust your workout accordingly!