The shock absorbers on a treadmill can give your step a bit of spring.
Treadmills use a variety of methods to absorb the shock of your running impact, which can translate to less stress on your joints than running over hard surfaces such as concrete. Running outdoors and on a treadmill have their pros and cons, but if joint pain is an issue, a treadmill with a powerful shock-absorbtion system might be what you need to continue running. Consult your doctor about running on a treadmill if you're new to the exercise or have joint or leg problems.
A wide selection of treadmills exist, but most share similar anatomy. They all have a deck, which is the material along the bottom of the machine that creates the stepping surface of the treadmill. The deck can be made of various materials including particle board and stronger medium-density fiberboard. The belt rotates around the deck; some belts have more cushion than others. More expensive treadmills include springs or shock absorbers under the deck.
Treadmill vs. Hard Surfaces
The ground reaction forces on a treadmill are significantly lower than on hard surfaces, according to the 2008 study "A Kinematics and Kinetic Comparison of Overground and Treadmill Running," published in "Medicine and Science in Sports and Medicine." Hard surfaces such as concrete and asphalt create jarring impacts on your joints with each step. Over time, this can lead to joint injury or pain. The treadmill provides a softer surface, cushioning each step to reduce joint impact.
Types of Shock Absorbers
Thinner decks on treadmills, such as 3/4 inches or less, often lead to bounce when you step. This softens the blow of each step, but it can throw off your cadence when running; it's best to use these types of treadmills when you walk instead of run. Runners should use decks at least 1-inch thick, although the shock absorption isn't quite as powerful. Belts offer different levels of cushioning to absorb shock; more expensive belts often provide more cushioning. Higher-end treadmills can have actual shock absorbers in the form of strategically placed springs or rubberized cushions under the deck. Some systems allow you to adjust the level of shock absorption to meet your exercise needs; softer surfaces make your workout harder, as if you were exercising on sand, while harder treadmill surfaces better replicate firmer outdoor surfaces.
More Like Outside
A major difference between outdoor exercise and working out on a treadmill is that you don't encounter the same natural incline changes and air resistance on a treadmill as you do on outdoor surfaces. Combat this by always using a slight incline on the treadmill to better replicate an outdoor walk or run. A 1 percent incline typically translates into walking or running over level ground outdoors. Many machines also offer you the ability to create an incline program that changes the incline to simulate running over flat surfaces as well as up and down hills while still taking advantage of the softer running surface on a treadmill.
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