Treadmills don't only provide the cardio workout benefits of walking or running - treadmills also have the same positive and negative issues for the human body.
Walking and running, whether on treadmills or pavements, are weight bearing activities. Weight bearing activities such as running on treadmills helps strengthen your bones by causing them to produce new cells. When your feet impact harder surfaces, the bone-building happens more quickly. The less give in the ground surface, the stronger the impact - and so, potentially, the stronger your bones. Treadmills with firm running beds provide more impact than softer beds.
Hard surfaces, whether sidewalks or firm treadmills, are better used for walking than jogging or running paces, because while impact helps build strong bones, too much impact can hurt your joints. For less impact, use treadmills that have belts with some give. If you have problem joints, you can get similar cardio workout benefits from elliptical trainers.
To work out on treadmills, no matter how firm or how fast, make sure you warm up for five minutes first. Start slow for one minute, then work for half a minute on your heels and half a minute on the balls of your feet; repeat. Speed up slightly and take longer strides for one minute. Increase the incline and walk for one minute, then return to your main workout level and increase the pace for a minute. Now it's time to do your stretching. And don't forget to wear quality shoes, which is important for cushioning impact as well as proper alignment.
