I also agree with the above replies, please note that weights should not be added to the lower extemeties for the same reasons. Knees would take on the most of the problem with legs snapping into extension quicker and harder than without weights. When clients want to add a boost to their walking program we find hills, and even repeat going up and down them, long stairways, or some lunge walking can get the heart rate to boost into an interval. I have used the Nordic walking Poles in Wisconsin, in the middle of summer, and aside from people cleverly yelling “Hey! Where’s the snow?!” they really add speed and effort to the walk.