There is considerable controversy these days on whether a treadmill or an elliptical trainer burns more calories. Treadmills and ellipticals are the #1 and #2 most popular selling fitness equipment.
Many dedicated treadmill users are switching to elliptical trainers. The appeal is the low impact, upper and lower body workout. Although treadmills still outsell elliptical trainers. The reason being, the most common form of exercising is walking and jogging.
Fast Fat Burner
In my research, I came across a number of reports and studies, and in general, it appears that both machines give comparable results in burning calories. In fact, using a calorie burn calculator on http://www.healthstatus.com, I found that a workout on an elliptical gives you the same results as running on a treadmill, but you burn fewer calories if you walk or jog on a treadmill.
Calories burned in 60 minutes by a 150 lbs. user:
Walking, 2 mph - 189
Walking, 3 mph - 297
Jogging - 477
Running, 7 mph - 783
Elliptical Trainer - 774
There was a basic flaw to the results, since it allowed you to compare calories burned at different levels of exertion on the treadmill, but not on the elliptical trainer. Often I see people working out on an elliptical at health clubs, and they are basically going through the motions. The calories they burn are no more than what you would achieve from a casual walk.
So which machine is better at burning calories?
It depends on which machine will motivate you the most and push you to the highest level of exertion.
If you are a devoted walker or runner then the treadmill is an obvious choice. The treadmill offers you a more forgiving surface in comparison to asphalt or concrete. It provides you with various programs that can add variety to your exercise. But to get results you need to crank up the speed and/or incline. Without pushing yourself, you will limit the number of calories you burn.
As mentioned, the elliptical trainer is growing in popularity due to the low impact, and combined upper and lower body workout. Since the machine moves in an elliptical motion and your feet never leave the pedals, it minimizes the impact and strain to your ankles, knees and back. This is an appeal feature to the aging baby boomer generation.
In addition, an elliptical trainer workouts both the upper and lower body simultaneously. The upper and lower body exercise utilizes the quadriceps, hamstrings, glutes, chest, back, triceps and biceps. Studies suggest that exercising numerous muscle groups increases fat burning efficiency. The larger the muscle mass involved in an exercise, the more effective that exercise is for improving fat mobilization, burning calories and building muscle endurance in an efficient period of time.
This would suggest that an elliptical trainer would burn more calories, but there is no denying that running also efficiently burns calories.
So which machine should you purchase?
If your joints are suffering from strain or just old age, and if you would like to exercise your upper body, the elliptical trainer is a good choice. For walkers, joggers or runners you can't go wrong with a treadmill.
In either case, to burn calories you need to exert yourself. Both machines offer a variety of challenging program. Most now come equipped with an "Interval Training" program. You alternate between high-level exertion and cool down periods. This type of training burns calories more efficiently in less time. With proper supervision from your doctor, try to push yourself to new limits.
I'm sorry I did not offer a definitive answer. It really is up to you to find the machine that best suites your needs, and will help you achieve your personal best.