## 4 Discussion  
The purpose of this study was to investigate the changes in pain intensity and tendon morphology following f-ESWT using ultrasound imaging to map these changes in patients with patellar tendinopathy. Our study focused on two main questions: immediate pain changes before and after f-ESWT and pain changes two weeks after the first f-ESWT session. On examining the immediate changes in pain before and after the first f-ESWT irradiation, we found no change in patellar tendon thickness but observed a significant decrease in NRS in both the first and second irradiations. Further, although there was no significant difference in tenderness and blood flow area between the first and second irradiation, there was a stark decreasing trend between the two sessions. Previous studies have reported that early pain relief is associated with the destruction of free nerve endings [16; 21]. In the present study, pain in the patellar tendon at rest decreased before and after irradiation, suggesting that f-ESWT irradiation may have destroyed nerve endings and had an analgesic effect. Further, the pathogenesis of tendinopathy involves [22; 23]. In our participants, this abnormal vascular network tended to decrease after f-ESWT, even though we checked the blood flow area before irradiation. We believe that the destruction of blood vessels by irradiation may have contributed to a decrease in fluid factors, such as neurostimulants, from blood vessels, thereby reducing the pain [2; 34]. In a comparative study of pain changes 2 weeks after the first f-ESWT, we found no change in patellar tendon thickness but observed a significant decrease in NRS between PRE(2) and POST(2) compared to PRE(1). We also observed a significant decrease in tenderness and blood flow area in POST 2 as compared to PRE(1). The recommended frequency of irradiation is three sessions at intervals of seven days [35]. In this study, we performed two irradiations performed every 14 days and observed significant improvements in NRS, tenderness and blood flow area in a short period. These results suggest that continuous f-ESWT irradiation over multiple sessions may enhance the pain relief effect and promote the recovery of tissue function [17]. Although this was not significant, we observed increasing trends in NRS, tenderness and blood flow area during the 7 days from POST(1) to PRE(2). Our subjects were college athletes who exercised regularly, and we did not add restrictions on physical activity during the study period. Therefore, they might have engaged in athletic activities during the f-ESWT period, which may have led to an increase in NRS, tenderness and blood flow area. Our results proved the immediate and short-term usefulness of f-ESWT in restoring the condition of an injured patellar tendon. Since the pain relief effect persisted even during exercise in our participants, we believe that f-ESWT is a useful treatment modality that does not require prolonged withdrawal for post-treatment recovery, unlike surgery. In the past, there have been reports that there was no difference in the effects of ESWT with and without irradiation, although subjective pain was reduced [36]. In addition, there may be cases where the tendon is not actually repaired even though it is subjectively improved, thus it is important to combine objective evaluation with subjective evaluation. There are several limitations in our study. First, while evaluating the blood flow area, it was not possible to distinguish between the abnormal vascular network produced during the inflammatory process and the neovascularization produced during the repair process. Second, it can only be tracked up to twice f-ESWT, not long-term. Thirdly, the sample size was small and including a heterogeneous group of unilateral and bilateral patella tendinopathy. Forth, the selection of ultrasound images is made by only one doctor, and the reliability of multiple doctors has not been examined.