||This article needs additional citations for verification. (December 2008)|
An elliptical trainer or cross-trainer (also called an X-trainer) is a stationary exercise machine used to simulate stair climbing, walking, or running without causing excessive pressure to the joints, hence decreasing the risk of impact injuries. For this reason, people with some injuries can use an elliptical to stay fit, as the low impact affects them little. Elliptical trainers offer a non-impact cardiovascular workout that can vary from light to high intensity based on the speed of the exercise and the resistance preference set by the user.
Elliptical trainers first entered the market in the 1990s. A more compact elliptical trainer was invented by Larry D. Miller for Precor and was patented in 2004. Miller created the idea for the machine by filming his daughter running alongside a car, while watching the motion of her legs. His idea was to take that exact motion and put it into a machine that puts less strain on the joints.
Most elliptical trainers work the user's upper and lower body (although some models do not have moving upper body components). Though elliptical trainers are considered to be minimal-impact, they are an example of a weight-bearing form of exercise. They can be self-powered by user-generated motion or need to be plugged in for adjustment of motion and/or for supplying their electronic consoles and resistance systems.
There are three types of elliptical trainers, categorized by the motor or "drive" location. The oldest elliptical design is the "rear drive" type. The "front-drive" elliptical was the second generation design. The latest design technology is the "center-drive".
On some models, the incline of sloping roller ramps beneath the pedal-links can be adjusted to produce varying pedal motion paths. The result of such adjustment changes the burdens on various muscle groups in the legs. Some models can vary the incline, resistance and stride length over the course of a workout according to a preset program. Some trainers can be driven in either a reverse or forward direction. Elliptical trainers are primarily driven via the legs, and most are combination designs having handle-levers attached to each pedal-link to enable a burden on the arms to provide a secondary source of driving power. The user grips the handles below shoulder height and pushes and pulls them while shuffling the feet back and forth within elliptically-shaped paths. Thus the oscillating handle motions are dependently coordinated with the constrained pedal motions. Poorly designed machines are too dependent on the user's leg power, producing excessive handle speeds due to mechanical ratios that do not provide enough advantage to the handle-levers. Consequently such machines feel to the user as if his or her arms are simply going along for the ride, rather than sharing in the work. The better models offer a harmonious combination of arm and leg exercise in the correct ratios.
Some manufacturers produce durable commercial models with extensive programs and made to withstand frequent use in a fitness club environment, at prices typically in excess of US$4,000. Models are available for home use at prices starting at about US$200.
An elliptical cross trainer is comparable to a treadmill in its exertion of leg muscles and the heart. Ellipticals produce an intermediate range of leg motion between that of stationary bikes and treadmills.
Studies have found that the rate at which calories are burned on an elliptical trainer is similar to that on a treadmill. Thomas Altena, a professor of nutritional and exercise physiology at the University of Missouri-Columbia, measured oxygen retention, lactic acid build-up, heart rate, and perceived rate of exertion to compare treadmills and elliptical trainers, finding that the "physiological responses associated with elliptical exercise were nearly identical to treadmill exercise".
Since users do not take their feet off the pedals, there is no footfall noise.
A 2002 study by the University of Idaho shows that varying the stride length on the elliptical trainer can recruit a larger variety of muscle groups. The study also showed that as the stride is lengthened, more calories are burned without any higher rate of perceived exertion by the user. This study is in agreement with the claims made about the adjustable stride length feature on some newer ellipticals.
Common usage 
Though procedures vary between various models, most are similar in that the user adopts a comfortable standing position with his or her spine in a neutral position (with a straight back). The user aligns their knees, hips and ankles; and ensures that their weight is distributed between the heels and the balls of the feet. The user grips the handrails in a smooth controlled motion, striding either in a forward or reverse motion, working through a full natural range of movement smoothly and continuously.
See also 
- The History and Features of Elliptical Machines Accessed 2010-01-04
- 2004 patent Accessed 2009-07-14
- Briley, John L. (July 27, 2004). "Bone Health: A Weight-Bearing Argument". The Washington Post. Retrieved 2008-12-12.
- Kozakiewicz, Hanna. "The Benefits of Using An Elliptical Cross Trainer". Retrieved 2013-02-07.
- Pierson, Vicki. "Elliptical Trainers: Giving The Treadmill A Run For Its Money?". Retrieved 2008-12-12.[dead link]
- American Fitness, "Treadmills vs. Elliptical Trainers," Jul/Aug2002, Vol. 20 Issue 4, p9.
- Browder, K. D; D. G Dolny (2002). "Lower extremity muscle activation during elliptical trainer exercise". Medicine & Science in Sports & Exercise 34 (5): S35. doi:10.1097/00005768-200205001-00198.