## 4 Discussion  
The primary aim of this study was to assess the relationship between reactive strength ability and sprint performance in field sport athletes. The results indicate that reactive strength is likely a key strength quality of sprint performance, particularly in mid-to-late acceleration phases. A notable finding from this study was that large relationships were observed between reactive strength and sprint times beyond 5 m; however, these were not statistically significant. This suggests that reactive strength may not be a key strength quality in early acceleration. Previous research has indicated that maximal isometric strength is strongly associated with early sprint acceleration (0-5 m) in male athletes, emphasising the importance of non-time-dependent strength qualities during the initial acceleration phase [38]. The lack of association between the physical quality of reactive strength and early acceleration performance may also be due to a lack of dynamic correspondence between the test (10-5 RJT) and the outcome measure (0-5 m time). Reactive strength testing utilised in this study (10-5 RJT) is a bilateral action characterised by short ground contact times (0.170-0.200 s), a large vertical force component (relative to the centre of mass) and small angular displacements at the hip and the knee [39]. The initial steps of early acceleration are unilateral in nature, tend to be longer in contact time duration, have a greater horizontal force component, demonstrate larger joint displacements at the hip and the knee, and are concentrically biased [40]. However, large relationships were observed between RSI and sprint performance at 5-10 m, 10-20 m, and 20-30 m segments. Reactive strength is likely a key strength component of mid-to-late-phase acceleration sprint performance. This finding is in agreement with research from [PERSON] et al. [3], which also demonstrated that the reactive strength index, measured with an \"ankle rebound jump\" protocol, was associated with mid-to-late-phase acceleration in sprimters but not with early acceleration phase. These findings suggest that reactive strength, especially as it pertains to ankle function, is a key component in the later stages of sprint acceleration. Further, supporting this, a study on football players found that higher unilateral RSI and isometric plantar flexor muscle strength were linked to faster 20 m sprint times and improved acceleration between 10 and 20 m [41]. This indicates that both the reactive and isometric strength of the ankle are crucial for sprint acceleration performance. These insights highlight the importance of ankle-specific reactive strength in sprinting, emphasising that training programs aiming to enhance sprint performance should consider incorporating exercises that target ankle function and reactive strength. The findings of this study and previous research [3] indicates that reactive strength becomes increasingly important as athletes enter the mid- to late-acceleration phase of sprinting. In such phases, the ability to produce high forces rapidly with short ground contact times is a key determinant of sprinting performance [18]. The dynamic correspondence between the test (10-5 RJT) and the criterion task (late-phase acceleration) is likely quite large, with late-phase acceleration exhibiting shorter CT\({}_{\text{SPRINT}}\), greater vertical force components (relative to the centre of mass) and smaller joint angular displacement during ground contact at the hip and the knee. An important and novel finding of this study is the identification of a potential mechanism by which reactive strength may positively influence sprint performance. The correlation between CT\({}_{\text{SPRINT}}\) and CT\({}_{\text{JUMP}}\) strengthens throughout the sprint phases from a moderate relationship in the early phases to a large significant relationship in the analysis of steps 15 and 16 (within the 20-30 m sprint distance).