The investigators developed the use of intramuscular peripheral nerve stimulation (PNS) for the treatment of HSP, which involves the temporary placement of a percutaneous intramuscular electrode to stimulate the axillary nerve motor points to the deltoid muscle. The deltoid muscle is stimulated for 6 hours per day for 3 weeks, causing comfortable, non-fatiguing contractions. This treatment, which occurs in the community setting, results in pain relief for up to 12 months when compared to treatment with a hemisling. A systematic review of randomized controlled trials (RCT) with pain as the primary outcome concluded that intramuscular PNS was the only treatment to provide long-term relief of pain for those with HSP. We have completed two RCTs that have demonstrated that a short-term PNS treatment (i.e., 3 or 6 weeks) provides pain relief. The first trial demonstrated efficacy in long-term pain relief in more than 60% of subjects for greater than 12 months. The second trial corroborated the finding that more than 60% of subjects receiving PNS achieved long-term pain reduction, and also showed that PNS reduces pain more than that achieved with physical therapy. The mechanism of action of PNS in reduction of HSP is not yet known. Thus, the primary objective of this RCT is explore the mechanism for HSP reduction.