Platelet-rich plasma (PRP) is an autologous concentration of human platelets and has been used for the treatment of tendon, ligament, and muscle injuries. However, it contains deleterious cytokines and growth factors that can cause fibrosis and inhibit optimal muscle healing. PRP therapy has grown in popularity over the past few years but the effect of the PRP with physical rehabilitation is not clear. PURPOSE: To assess the effect of physical rehabilitation with PRP injection on the treatment of hamstring strain injuries. METHOD: Eight physically active males (age 22.7±3.6) with acute hamstring strain injuries and nine matched controls (age 21.9±2.8) were recruited as research participants. Approximately 60 mL of blood was drawn from an antecubital venipuncture then centrifuged to approximately 5-6 mL of PRP by BioMet System. The PRP was injected into the biceps femoral muscle using ultrasound guidance with a single injection that occurred after 5-7 days of injury and before an 8 weeks physical rehabilitation program. After 48 hours of PRP injection, the serums were vascular endothelial growth factor (VEGF) (0.346 ± 0.182 vs 1.504 ± 0.463 pg/L), platelet-derived growth factor (PDGF) (0.352±0.11 vs 5.72±1.57 pg/L), and Insulin-like Growth Factor-1 (IGF-1) (0.577±0.28 vs 1.101±0.381) (p \u3c 0.05). Dependent measures were taken immediately before the PRP injection (pre-test), and after the 8-week rehabilitation program (post-test) for the two groups and included hamstring force (HF), knee flexion range of motion (ROM). RESULTS: There were no significant differences between the posttests of the two groups in hamstring force (105.75±3.18 N vs 107.06± 1.64 N), and (ROM) (148.62±0.78 N vs 147.36± 0.88 N) (p \u3e 0.53). CONCLUSION: Despite the theoretical benefits of PRP to regenerate muscle tissue and expedite return to activity, results indicated that PRP did not affect HF or ROM values when compared to a control group not receiving PRP