A treadmill is a stationary exercise machine designed to promote cardiovascular fitness and leg strength. Treadmills are commercially available in a number of different designs, all of which accommodate both walking and running at a variety of speeds. The stair climbing machines, often referred to by the Stairmaster trade name, are similar in their training purpose to the treadmill, as each provides for continuous forward motion.

Treadmills were first developed in the 1800s as a means of producing power; animals were employed on treadmills to power grain threshing machines and other agricultural equipment. The first treadmill designed for an athletic purpose was built in the early 1950s in the United States, so that medical doctors could perform accurate heart monitoring on patients with known cardiovascular problems. Modern treadmills and stationary exercise bicycles are the most common method for performing electrocardiogram (ECG) and blood-pressure testing on persons at risk for heart disease.

A treadmill is typically constructed with a set of rollers or other repetitive motion devices overlaid with a rubber compound running surface. The modern treadmill is equipped with a computerized digital screen and various monitors that display the controls that govern the speed and the incline or decline of the running surface. Most treadmill control mechanisms are compatible with various brands of heart monitors and biofeedback devices, which permit the treadmill users to obtain a comprehensive reading as to their workout quality. It is for this reason that the highly controlled exercise obtainable through a treadmill is very useful for persons with a predetermined cardiovascular condition, where the user can operate the device at a rate consistent with a known safe limit.

The treadmill is not a low impact exerciser in the fashion of an elliptical machine or a stationary bicycle, in that the running motion performed on a treadmill is identical to that of an athlete running anywhere. The surface of the treadmill, as a rubber construction, is often more forgiving than that of the roads used by distance runners, but there will be significant forces directed into the lower legs and feet in a treadmill running session.

More sophisticated treadmill models will permit both the significant adjustment of the ramp elevation on which the user runs, as well as a reverse motion, which permits forms of running training. Reverse action on any stationary machine is most effective in maintaining the proper distribution of muscle power between the quadriceps and the hamstrings of the upper leg; an imbalance in their typical optimal ratio of quadriceps to hamstring, 3:2, is a primary factor in the cause of muscle pulls and strains in these structures.

Stair climbing machines are often used by persons seeking general cardiovascular fitness benefits as well as a more specific cross training effect. Stair climbers are built with similar computerized control equipment to those provided on treadmill machines, permitting the user to vary the speed and the intensity of each workout. Stair climbers also have a reverse motion available in their operation, for the same benefits as created by the treadmill reverse feature. Other than the day-to-day act of climbing a

Exercising on a treadmill can be good cardiovascular exercise and is an alternative to running outdoors.
set of stairs, the stair climbing machine does not replicate the movements of any particular sport.

The chief distinction between the treadmill and the stair climber is the true low impact nature of the stair climber exercises. On a stair climber, the contact between the user's foot and the machine is constant, limiting the impact directed into the foot and leg to those of the force generated in the climbing motion. On all such devices, hand rails are constructed along the area where the user is positioned to perform the exercises. The most demanding workouts on both a treadmill and a stair climber are those where the user does not hold the handrail during exercise. The less external balance provided to the user by the rigid machine, the more reliance that the user must place upon the abdominal, lumbar (low back), and groin muscles to maintain balance. The development of these muscle and tissue structures is the building of the core strength of the athlete. Both stair climbers and treadmills provide a beneficial resistance training effect for the musculoskeletal structure of the legs, hips, and pelvis.

There are differences in the fitness benefits obtained between running outdoors and a treadmill workout. All other factors being equal, a runner exercising outdoors will expend a greater amount of energy than a similarly situated athlete on an indoor treadmill. The treadmill, in a controlled, indoor environment, eliminates external factors such as cold air and wind resistance. For an outdoor runner, wind resistance may account for up to 5% of the energy expended by the runner. The treadmill runner derives a benefit from the manner in which the machine operates, as the rotating motion of the treadmill will pull the runner's feet slightly backwards with every stride, reducing the energy the runner requires to push off the running surface with each step. At greater running speeds, the outdoor runner will expend as much as 9% more energy than the treadmill runner.

For runners who desire a controlled environment, either for health reasons or to avoid adverse environmental conditions, the treadmill and the stair climber are excellent cardiovascular options.

Tri-athlete in the waves.

SEE ALSO Cross training; Fitness; Health; Stationary bicycles, elliptical trainers, and other cardio training machines.