Is there a difference between running on a treadmill or using an eliptical

With the weather this weekend at wind chills below freezing and not much relief in sight many of us are forced inside to train.  Typically we would slog it out on the treadmill, but over in the other line of cardio machines are the elliptical, with their claim to fame being they provide less impact to the joints.  A big question arises, are the workouts similar?

Surprisingly they have not been compared in terms of oxygen consumption, energy expenditure, and heart rate during a single session until Brown et al in , Comparison of Energy Expenditure on a Treadmill vs. an Elliptical Device at a Self-Selected Exercise Intensity, Journal of Strength and Conditioning Research 2010

The main finding of this investigation was that when healthy, non-active, college-aged, men and women exercise at the same level of perceived exertion, there are no differences between the elliptical and treadmill in terms of total oxygen consumption, or energy expenditure. However, when compared to the same level of perceived exertion, exercise on an elliptical results in a higher heart rate, utilizes a higher percent of maximal oxygen consumption, and has a higher respiratory exchange ratio than does exercise on a treadmill. One explanation is that the arms are more active in using the elliptical, which could also result in a higher heart rate. The finding that total oxygen consumption, VO2peak, and total energy expenditure were higher in males than females was not unexpected, due to the larger overall body mass of the males compared to the females.

Overall, the results of this study suggest that the elliptical can be a viable alternative to the treadmill for those seeking improvements in cardiovascular fitness and overall health. With the added benefit of lower impact on the joints, the elliptical then becomes a great cross-training method for those who perform a large volume of  running. In addition for quality training sessions for either aerobic threshold or VO2 max, periodic use of the elliptical may be of benefit as it elicits higher heart rate and VO2 peak at the same level of perceived exertion and the elliptical reinforces that concept of shorter strides and quicker turnover which appears to be beneficial for injury reduction

Specifically from the study
• There were no differences in RPE (rating of perceived exertion) between treadmill and elliptical.
• There were no differences in total oxygen consumption between the treadmill and the elliptical, However on the elliptical the subjects elicited a higher percentage of VO2peak than did the treadmill.
• There were no differences in energy expenditure between the treadmill and the elliptical.
• The mean heart rate for both genders during elliptical exercise was higher than treadmill exercise.
• Mean RER (respiratory exchange ratio) for both genders during elliptical exercise was higher than treadmill exercise.