The elliptical trainer (also known as a cross-trainer or also just the elliptical) is a stationary exercise machine that provides an aerobic workout. Ellipticals combine the features of a stair-step with a ski machine; you stand on pedals that move on an elliptical track with a roller.With most elliptical trainers, the user can vary the intensity, which is based on resistance and hill preferences. Seniors in particular should find the elliptical trainer a particularly useful device. Aging adults, who are prone to knee pain but need some sort of mechanism for indoor cardiovascular workouts will find the elliptical particularly noteworthy. Unlike the treadmill, its stationary counterpart, the elliptical stimulates the experience of running (or walking) without putting excess pressure on your knees. In addition to the low-impact benefit of the elliptical, there are a number of optional features that seniors might want to keep an eye out for. Each individual body ages at its own unique pace so it is essential to understand the relationship between the machine and the biomechanics.