When not to use it:
- Going backwards or sideways (laterally). Going backwards or sideways on the treadmill is a great way to hurt your knees or back, and not help you laterally or backwards on the ground.
- Going very fast. The higher the speed, the greater the friction forces and thus stress on the knees, feet, and ankles.
- As a crutch to hold onto. Holding on to the handles at a steep incline will put the body at 90 degrees relative to the ground (the same as it is when walking on flat land) and now you are using your arms for pulling to keep you on the treadmill. You’re better off with a zero grade and not holding on. Isn’t it great when simpler is better?
- As your primary cardiovascular tool. The ground outside should take far more of your walking and/or jogging time if you value the benefits and want to decrease the unnecessary risks of exercise.
When to use it:
- Bad weather. If the weather or outside conditions are overly stressful, it’s better to train indoors for your walk, jog, or run.
- As a gauge of speed improvement. When going long distances at a walking pace, or just a longer jog/run, having the treadmill show your speed is immensely helpful. It sure beats trying to stare at your phone or your watch while running.
- For short-term convenience. You’re at the gym and want to get a few minutes of walking or jogging in, but where you are is neither convenient nor time-efficient to do outside at the moment.
- As part of your jogging or walking cool-down. You don’t have to look where you’re going, and you can (gasp) watch tv without worrying about running into anyone or vice versa.
And make no mistake, walking or running is far more important daily activity than swimming, elliptical, biking, rowing, or any other form of cardiovascular activity or cardiovascular equipment usage. It’s not even close. They all have value, but walking or running (whatever you’re able to do) provides the most value, and barring current injury or ailment, far less risk.