Treadmills let you get in a great cardiovascular workout in all seasons and weather. You may worry about the risks to your knees, though -- especially if you've already suffered a knee injury. While treadmill running does present risks for your knees, they are manageable with proper training and form. Ask a trainer or doctor to coach or guide you if you have pressing concerns.
Your knees comprise delicate tendons and ligaments that hold together and interconnect with your leg muscles. A common running injury to the knee is runner's knee or a dull pain behind the knee cap. This is usually attributed to strength imbalances in the thighs, which causes cartilage to grind against the kneecap. Incorporating lower body strength training into your workout will help solve runner's knee. You may also suffer shock injuries or tears to the ligament or tendon. All of these are risks of running in general, though, and aren't more likely from a treadmill.
When it comes to shock absorption, treadmills are actually better for you than running on pavement. Because your knee is a primary shock absorber when you run, a treadmill can go a long way toward preventing injury. Some treadmills absorb shock better than others. Thicker belts or even shock absorption decks under the treadmill decrease the risk of knee injury. If you've hurt your knee before, look for treadmills with as much shock absorption as possible.
Proper Running Form
Your form when you run on a treadmill has a lot to do with your risk of knee injuries. If you run with poor form, you can twist your feet or legs, hurting your knee. Run with your posture upright and relaxed. Some treadmill runners may step ahead of their center of gravity because their posture is incorrect or because they aren't used to various inclines. This risks knee injury. Land on the balls of your feet. Avoid landing on the heels. Proper landing allows your body to distribute shock appropriately. Keep the knees slightly bent at all times. Consult a trainer if you're unsure your form is accurate.
Treadmills turn at the same speed, whether your body is ready or not. Start off slowly and manually adjust the speed as you warm up. Starting off too fast and maintaining a high intensity run before you've properly warmed up and settled into the proper running form can injure your knees. Adjust the speed as many times as necessary to accommodate your knees and body, providing for a proper warm up, run and cool down period.
Overtraining and Knee Injury
Overtraining leads to an increased risk of knee injury. Because your knees are in a constant state of movement when you run, you may risk irritating the tendons and ligaments. You can run safely on a treadmill up to five days a week once you're conditioned properly, but if you feel even twinges of pain, give your body one or two days for recovery.