We've previously evaluated several models of elliptical exercisers, nonmotorized machines that feature orbital lower-body motion and a push/pull upper-body motion. One important measurement to capture is a model's functional response to a workout.

We measure breathing and cardiovascular indications of how the body produces the energy necessary for a workout. We use a telemetry system to monitor the heart rate of an exercising panelist, and chemical sensors to monitor samples of expired breath. With all of this information, we are able to determine how much effort each elliptical exerciser demands of a panelist, and if the model offers a workout that will improve health and fitness.

As part of our overall assessment of each tested model, we also look carefully at design: Is the equipment comfortable on the joints? Are the features easy to use? Is the equipment noisy? The evaluation of these "human factors" contributes in a significant way to our product Ratings.