The elliptical trainer was originally designed by an inventor who came up with the idea for the elliptical motion by filming his daughter running alongside his car, then replicating that running motion in a machine that gave running benefits, but put less strain on the joints.

And he was right. A study at the University of Missouri measured oxygen utilization, lactic acid formation, heart rate, and rating of perceived exertion on an elliptical trainer as compared to a treadmill, and found that the elliptical exercise was nearly identical to the treadmill exercise in every respect – but the elliptical trainer created far less joint impact.
Another study compared muscle activity patterns of the quadriceps and hamstrings in walking on the ground, walking on a treadmill, stationary bicycling, and the elliptical trainer. The elliptical trainer produced significantly greater quadriceps utilization and greater quadriceps and hamstring coordination than any of the other modes of exercise! And a study at Willamette University found that when you pedal backwards
on an elliptical, your quadriceps utilization skyrockets even more.

On an elliptical trainer that includes arm motion, a shoulder, chest, biceps and triceps workout can be incorporated simultaneous to a lower body cardiovascular workout. In addition, the upright posture on an elliptical trainer will utilize more of your core muscles, and if you go “hands-free” without using the railing on an indoor elliptical trainer, you can increase balance and posture training effects too.

In short, you can save a ton of time by working your upper body muscular endurance, lower body muscular endurance, cardiovascular fitness, and core all at the same time on an elliptical trainer.