## 4 Discussion  
The objective of this study was to analyze the influence of hamstring injury history on the neuromuscular fatigue produced by an RSA test in elite female football players. For this purpose, the incidence of neuromuscular fatigue was determined through a CMJ test,  
Figure 4: Percentage difference between the best time compared to the worst time to run a split (%DiffbvsW) through RSA. Control: Subjects without previous hamstring injury; Hamstring: Subject with previous hamstring injury. Figure 3: Percentage difference between SplitTT and Ideal Split: percentage difference between the time to run a specific number of splits and the time if these splits were run as the best of them. Control: Subjects without previous hamstring injury; Hamstring: Subject with previous hamstring injury. * Significant difference between 0–10 m and 0–20 m in the hamstring group considering the first 20 m of the sprints (\(p<0.005\)). harmstring test, and the performance variables of the RSA test itself in subjects according to the hamstring injury history. The main findings from the present study were that, in subjects with previous hamstring injury, the performance was impaired compared with the control group: (1) in the initial meters of the sprint during a RSA there was a higher percentage difference between \(\text{Sprint}_{\text{TT}}\) and Ideal Split in 0-10 m compared to 0-20 m in the hamstring group and (2) in situations of high fatigue there was a higher %Diff1 vs6 compared to %Diff1 vs5 in the hamstring group compared with the control group. The results obtained when analyzing the initial 20 m of the sprints showed that the percentage difference between \(\text{Sprint}_{\text{TT}}\) and Ideal Split decreased in 0-20 m compared to 0-10 m in the hamstring group, whilst it remained constant in the control group. In other words, \(\text{Sprint}_{\text{TT}}\) was further from Ideal Split in 0-10 m than at 0-20 m in the hamstring group, whilst it was similar in the control group. This suggests that performance suffers a larger decline in the first few meters of the sprint in subjects with previous hamstring injuries. Hamstring muscles are known to play a key role during the acceleration phase of the sprint [19]. Therefore, there was a higher decrease in performance in these female elite soccer players with previous hamstring injury in the initial meters of the sprint when acceleration is maximal. This is an important finding because these players had their last hamstring injury at least one season ago and they were theoretically perfectly recovered, however, they may still have a muscular disability. They were not able to apply the same strength and power during the first meters of the RSA test, and they have a lower opportunity to take advantage of the competition and might have a higher re-injury risk [65]. When comparing the lasts two sprints to observe the evolution of performance under fatigue conditions, the %Diff1 vs6 was higher compared to the %Diff1 vs5 in the hamstring group, whilst it was not different in the control group. The performance from the 5 th to the 6 th sprint compared with the 1 st sprint was more reduced in the hamstring group and it indicates that performance is more impaired in a situation of fatigue in the hamstring group. This agrees with a previous a study [66], which showed a larger decrease in performance in soccer players reporting former hamstring strain injury during an RSA (8 \(\times\) 20 m) [66]. In this sense, other authors [67] observed a lower biceps femoris activity in the previously injured limb during the final phase of the sprint [68]. Furthermore, since fatigue has been associated with hamstring injuries [33,34], the higher reduction in performance associated to fatigue in subjects with previous hamstring injury might predispose these subjects to a subsequent injury [67].