A quick comparison:
When you compare treadmills to elliptical trainers, you can't help but notice that the elliptical trainer offers an impact-free workout. With the elliptical, there is no impact on the ground, which may appeal to people who need a gentler workout because of joint problems or pain. The treadmill offers more impact, which helps strengthen the bones.
One obvious point that is in favor of treadmills is that it provides a better training experience for a dedicated runner/jogger than an elliptical trainer. If you are training for a marathon or even a 10k, and you don't want to go outdoors too often during the colder months, you are certainly better off with a quality treadmill.
That being said, if you are looking for a quality cardiovascular workout with the maximum amount of efficiency, the elliptical is an excellent choice. Most elliptical trainers give you a total body workout if you have dual action handlebars for your arms and foot pedals for your legs, whereas treadmills focus more on your lower body as they simulate the jogging experience. What is even more interesting, according to recent studies, is that the lack of impact on the joints allows the user to burn roughly the same amount of calories as treadmills with the impression of putting less effort.
Therefore, it is no wonder that ellipticals have been the machine of choice for seniors exercisers with knee problems, as well as physical trainers who are involved in rehabilitating their clients.
This is what Thomas Altena, an exercise physiologist at the University of Missouri-Columbia, had to say: "The physiological responses associated with elliptical exercises were nearly identical to treadmill exercises." He went on to conclude that "both exercise machines are effective for increasing the amount of calories burned and for producing cardio respiratory health and training benefits..."
Finally, one feature which is often overlooked about elliptical trainers is the ability to add variety to your aerobic workout. Whenever anyone is on an exercise plan, one of the biggest challenges he faces is to stay motivated and interested in his workouts. With the treadmill, the ability to change the incline, as well as the intensity are big pluses, which has contributed to its popularity over the last decade. The elliptical trainer matches these features and has a few additional ones of its own.
In addition to changing the cross ramp incline (which is available in Precor models) as well as varying the intensity, you also have the option to not use the handlebar and focus on your lower body. Although this option is not used often, it does add variety to your workout.
However, the most critical feature, and what separates the elliptical trainer from many other exercise machines when it comes to variety, is the forward and reversible feature on the foot pedals. When you are going forward, you feel like a cross country skier hitting the long slopes. However, when you reverse your pedal motion, you can target your lower body in a completely different way. Without question, you are targeting your quadriceps muscles and will soon feel them burn after a few minutes.