Power speed harnesses 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 backward with a power speed harness are as follows:

First, you will need to put the shoulder harness on backward so that the lead line is in the front of the body. Assume the starting position, then run backward for several yards (30 to 40 yards is typical). Tow the load using maximum leg power. Try to incorporate the use of hand [running] motions. Doing so will enable you to perform the drill faster.

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.