Power speed harnesses are training devices that can be used to compliment running drills. They are ideal if you want to improve overall quickness and driving power in the legs. There are a number of ways to add resistance to a power speed harness. Typically, a weighted sled is used. However, just about anything that creates "drag" will work. Examples might include old tires, wooden logs, etc. Instructions for running with a power speed harness are as follows:

First, secure the shoulder harness. Most will have a waist belt with a buckle in front. Tighten it as needed. Assume the starting position, then sprint for several yards (approx. 30 to 40 yards is typical). Tow the load using maximum leg power. Depending on the amount of weight used, you may have to walk instead of run. To add difficulty to this exercise, simply increase the load, increase running speed, or increase running distance.