The purpose of this study is to evaluate the safety and effectiveness of electrical stimulation (low levels of electricity) on low back pain. This study involves a Peripheral Nerve Stimulation (PNS) system. The System delivers mild electrical stimulation to the muscles in the low back. The System includes up to four small wires (called "Leads") that are placed through the skin into the muscles in the low back. It also includes up to four devices worn on the body that deliver stimulation (called Stimulators).