We aim to recruit 40 patients who are receiving ultrasound-guided intratendinous (IT) or intramuscular (IM) PRP injections. Blood will be drawn immediately before (baseline); 15 minutes after; and 3, 24, 48, 72 and 96 hours after receiving PRP therapy. A fraction of the therapeutic PRP preparation will be isolated for growth factor analysis. Serum concentrations of growth factors will be quantified by ELISA. Statistical analyses will be conducted to assess the change in each growth factor following PRP injection. To understand the impact of injection site on systemic growth factors, changes in concentration will also be compared between the intratendinous and intramuscular groups.