Table 1. Data Summary for the Growth Factors after PRP Injectiona
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Figure 5, The concentration of the growth factors after the PRP injection. PRP, platelet-rich plasma; hGH, human growth hormone; IGF-1, insulin-like growth factor-1; FGF-2, basic fibroblast growth factor; VEGF, vascular endothelial growth factor; PDGF, platelet-derived growth factor.
The performance of the growth factors after a single PRP injection was enhanced and increased significantly from 24 until 96 hours. Indeed, hGH was peaked within the 24-hour window, although the results were not significant after 4 weeks or 8 weeks. Similarly, IGF-1 is significantly increased by 24 until 96 hours after PRP, while its’ activation was decreased after 4 weeks and 8 weeks but with significantly difference compared with the pretest and the control group 8 weeks’ test. Furthermore, IGF-1 is generated in the liver in response to hGH, is the primary downstream mediator of hGH, and is the most specific marker of supraphysiological hGH exposure  .
Figure 6. Difference between the case and control group in the concentration of the Growth Factors after 8 weeks. hGH, human growth hormone; IGF-1, insulin-like growth factor-1; FGF-2, basic fibroblast growth factor; VEGF, vascular endothelial growth factor; PDGF, platelet-derived growth factor.
Despite that both groups performed the same rehabilitation program, our study reported a significant increase in the growth factors for the control group after 4 and 8 weeks (Table 3, figure 6). However, the values of the case group after 4 weeks for the case group were more advanced than the 8 weeks’ values of the controlled (Figure 7,8). Therefore, the PRP injection enhanced the concentration of the growth. It is notably that the physical measurements of hamstring force and knee flexion range of motion were not significant at either 4 or 8 weeks. Wallace et al demonstrated that an acute bout of exercise increases total circulating IGF-1 by only about 20%  .
Figure 7, Difference between the case and control group in (NFROM) Knee flexion range of motion after 8 weeks.
Figure 8, Difference between the case and control group in (HF) Hamstring Force after 8 weeks.
By comparison, participants in case group who treated with PRP and exercise program. Our study demonstrated a 38% increase in IGF-1 in case group and 9.5% in control group. Relative to baseline, suggesting that PRP treatment activates the hGH-IGF-1 pathway but that a single PRP injection is important to combined with the exercise to maximally stimulate.   (Table 3) (Figure 6). We also observed FGF-2 and VEGF also peaked after treatment with PRP. Fibroblast growth factor contributes to angiogenesis by stimulating the proliferation of endothelial cells to enhance the proliferation of satellite cells, which are the stem cells of mature muscle . Basic fibroblast growth factor may enhance athletic performance by inducing muscle hyper- trophy and increasing oxygen transport. Vascular endothelial growth factor is a powerful stimulator of angiogenesis and could have noteworthy performance-enhancing effects if it entered systemic circulation and exerted its effects in tissues other than the site of injury .
The potential effects of autologous biological substances to hasten muscle healing were reported in several case reports   . Borrione et al  noted that athletes with grade 3 muscle strains treated with PRP showed earlier functional improvement and more complete recovery than those treated nonoperatively. Hamid et al  demonstrated that a single PRP injection was effective in accelerating recovery for grade 2. However, the PRP Group achieved full recovery significantly earlier than controls and returned to play after 27 days while control group returned after 43 days. Another approach successfully treated an athlete with a grade 2 semimembranosus muscle injury with a single 3-mL infiltration of platelet-enriched plasma under ultrasound guidance. The athlete was pain free and allowed to train at the preinjury intensity 21 days after treatment . The effect of a preparation rich in growth factors (PRGF) to hasten muscle recovery was reported in a 35-year-old professional bodybuilder diagnosed with a right adductor longus rupture. The athlete successfully returned to competitive training within 1 week after the third PRGF injection . The effect of PRP in accelerated and associated a hamstring injury was also observed in the current study. The PRP preparation contained a high concentration of several growth factors including TGF-b, FGF-2, and insulin-like growth factor-1, but the amount of platelets and WBCs present was not stated. Additionally, the actual effect of PRP on soft tissue healing is not fully understood,22 our findings supported the possible role of higher growth factors (concentration level) in hastening recovery as postulated by previous researchers   . Sanchez et al reported full functional recovery of hamstring and adductor muscle injuries 2 times faster in 20 professional athletes treated with a PRGF .
Similar designed study by Rettig et al was investigated the effects of an autologous PRP injection and was retrospective case-control study conducted to determine the effect of the PRP on return time to play after acute hamstring injuries. The study included 10 professional National Football League (NFL) players with acute hamstring injury. The participants were divided equally into PRP and Control groups. Under ultrasound guidance the PRP group patients were injected once with 6 mL of PRP. Both groups were performed the same rehabilitation program. Several differences were identified between the study by Rettig et al and the current study. For instance, the