a good method to burn the maximum amount of calories possible is interval training, which is where one goes from say for example, running fast on the treadmill for 30 secs, then walking on the readmill for 60 secs, and keep repeating for about 20/30 mins it seems like it would get annoying to keep changing the settings but it actually prevents me from getting bored!! also this would apply to walking very fast, then walking slowly, i guess you could do this with the crosstrainer.