Reactive Strength Ability Is Associated with Late-Phase Sprint Acceleration and Ground Contact Time in Field Sport Athletes

Abstract

This study investigated the relationship between reactive strength and sprint acceleration performance in elite under-21 hurling athletes. Reactive strength was assessed using the 10/5 Repeated Jump Test (RJT), while sprint performance was measured over 30 m with split times at 5, 10, 20, and 30 m. Twenty-four male players participated in the study. The results revealed large, significant correlations between reactive strength index (RSI) and sprint times in the 5–10 m, 10–20 m, and 20–30 m splits but not in the initial 0–5 m phase. Further analysis showed that athletes with higher RSI scores exhibited significantly shorter ground contact times (CT_SPRINT) and superior sprint performance in the 20–30 m segment without compromising step length. These findings suggest that reactive strength plays a crucial role in mid-to-late-phase acceleration, likely due to the ability to produce force rapidly during short ground contact durations. The study also identified a significant, negative correlation between RSI and CT_SPRINT, indicating a possible mechanical link. These results support the inclusion of reactive strength development in training programs aiming to enhance sprint performance, especially in field sports requiring repeated high-intensity sprints.

1. Introduction

Team sports often involve intermittent, high-intensity activity combined with periods of lower-intensity movement, requiring athletes to be versatile and dynamic in their physical, tactical, and technical roles [1]. These sports, which frequently feature 70 to 90 min matches, are typically played by teams of varying sizes, including a mix of goalkeepers and outfield players [2]. In many team sports, sprinting is a critical component of performance. Speed and acceleration are key attributes that can influence both offensive and defensive outcomes. For example, rapid acceleration over short distances, such as 20 m, often proves decisive in gaining possession, executing attacks, or neutralising threats [3,4]. Elite players can engage in high-intensity actions every 20 to 30 s, leading to numerous sprints and accelerations throughout the game [5]. Consequently, the ability to accelerate quickly is a vital skill that can determine the success of individual plays and, ultimately, the overall outcome of the match. As a result, developing the physical qualities that enhance sprint performance is of significant interest to athletes and coaches in team sports, as these attributes can be crucial for achieving success on the field [6].

Sprinting is frequently described by step kinematics. Step length is the distance between alternating contacts of each foot, step frequency is the rate at which steps can be reproduced, and ground contact time (GCT) is the duration of time when the leg is in contact with the ground and flight time is the period when the athlete is airborne. Sprinting velocity is the product of step length and step frequency [7]. Improving sprint performance requires an increase in step length, step frequency, or both [4]. A high step length [8] and frequency [6,9] are important for acceleration. Further, lower GCTs are associated with efficient acceleration [6,9]. The ground contact phase of sprint acceleration is considered a fast stretch shortening cycle (SSC) activity with force expressed maximally in GCTs of <0.25 s [10] under the commonly reported threshold for fast versus slow SSC actions [11]. Therefore, acceleration capacity requires an ability to develop force in short time periods via the fast SSC and is influenced by specific strength and power capacities [6]. It has been postulated that reactive strength is a physical quality that influences acceleration and overall sprint performance [3,6].

The stretch shortening cycle (SSC) plays a crucial role in sprint acceleration by enhancing force production through the rapid transition from eccentric to concentric muscle actions [12]. In the initial stages of acceleration, GCTs are relatively long (~200 ms), providing more time for force development through a slower, force-dominant SSC [13,14]. During this phase, athletes generate high horizontal ground reaction forces (GRFs), which are essential for overcoming inertia and driving forward propulsion [13]. These forces are characterised by strong horizontal braking–propulsive impulse, emphasising the importance of horizontally directed force application in the early strides [15]. As acceleration progresses and velocity increases, GCTs decrease substantially (~120–140 ms), limiting the window for force application. To remain effective under these time constraints, the SSC must function more rapidly, relying on increased muscle–tendon stiffness, preactivation, and efficient elastic energy utilisation [16,17]. Consequently, the orientation of GRFs gradually shifts from horizontal to vertical, reflecting a biomechanical transition from force production to velocity maintenance and increased stride frequency [3,18]. In the later stages of acceleration, fast SSC characteristics—such as shorter GCTs, minimised joint displacement, and efficient stiffness regulation—become critical for sustaining high stride rates. Importantly, reducing braking forces during this phase has emerged as a key performance determinant. Research shows that high-level sprinters are particularly effective at minimising horizontal braking impulses, allowing for smoother transitions and more efficient forward propulsion. This ability distinguishes them from team sport athletes, who typically exhibit greater braking forces during late acceleration, contributing to less effective sprint mechanics [19]. Thus, the progressive adaptation of the SSC function not only underpins the shift from force to velocity dominance but also plays a pivotal role in optimising mechanical efficiency and sprint performance in elite populations.

Reactive strength has been defined as the capacity of the lower limbs to bear a stretch load and subsequently switch rapidly from eccentric to concentric contraction [20]. It has also been described as an athlete’s ability to rapidly generate force under a high eccentric load [21]. The reactive strength index (RSI) has been developed as a global descriptor of performance in fast SSC tasks and is strongly associated with vertical stiffness (r = 0.67; 0.42–0.82) [4], which is a key determinant of sprinting performance [18]. The RSI is a ratio of jump performance to contact time and is typically assessed in tasks such as a drop jump (DJ) or repeat jumps. It has also been suggested that reactive strength could enable the conversion of the eccentric load into concentric force over a shorter duration [6]. As such, it has been postulated that reactive strength may influence an individual’s sprint performance. Reactive strength has particularly been associated with early-phase acceleration (0–5 m; r = 0.65, 0–10 m; r = 0.55) [6] and late-phase acceleration (14th–19th steps; r = 0.48–0.54) [3].

Lockie et al. [6] examined factors that differentiate acceleration ability over 5 and 10 m distances in male field sports athletes. Reactive strength was assessed via a DJ from a 40 cm drop height. Contact times in the reactive strength assessment ranged from 0.25 s (fast group) to 0.28 s (slow group). Across both groups, the RSI was significantly correlated with acceleration performance from 0 to 5 m (r = 0.65, p = 0.00) and 0 to 10 m (r = 0.55, p = 0.01). Faster athletes displayed significantly shorter GCTs from stride to stride over 10 m acceleration compared with their slower counterparts. Fast players also demonstrated significantly greater reactive strength compared to slower players. Reactive strength was the largest differentiator between slow and fast athletes across a range of tests, including the countermovement jump (CMJ), bounding tests and the 3-repetition maximum (3RM) back squat. The authors suggest that reactive strength qualities may help to explain the lower GCTs attained by the athletes with better acceleration in the short sprints.

Whilst Lockie et al. [6] demonstrated the association between reactive strength and early-phase acceleration (0–10 m), such associations may be even stronger in the main acceleration phase and maximal velocity phase, where GCTs are lower and performance is more reliant on the application of force, in shorter time periods, vertically into the ground. This has been substantiated by the work of Nagahara et al. [3], who observed in trained sprinters that performance in a reactive-strength-dependent task (ankle jumping) was significantly correlated with overall 60 m sprint performance. The ankle jumping task was ankle dominant and utilised contact times of 0.132 s (±0.008 s). Rebound continuous jumps with contact times of 0.149 s (±0.01) were not significantly correlated to overall sprint performance. A step-by-step correlative analysis showed that ankle jumping performance was most strongly correlated to late-phase acceleration performance (from 23 m to 34 m of the 60 m sprint). Late-phase acceleration is characterised by shorter GCTs and a more vertical application of force into the ground than early-phase acceleration [22]. Late-phase acceleration is characterised by shorter ground contact times (GCTs) and a more vertical application of ground reaction forces (GRFs) compared to the early phase [22]. During early acceleration, a pronounced forward lean and longer GCTs facilitate the production of large anterior–posterior (horizontal) forces necessary to overcome inertia and initiate forward motion [3,13]. As acceleration progresses, athletes adopt a more upright posture and shorter GCTs, resulting in a shift toward a more vertically oriented force application. Consequently, the anterior–posterior component of the GRF decreases in magnitude, though it remains essential for continued propulsion. This necessitates a more rapid and efficient application of horizontal force within a reduced time frame [23,24]. Such findings have been replicated in the literature across varying athletic populations and varying sprint distances. Hennessy & Kilty [25] reported RSI to be significantly related to 30 m (r = −0.79) and 100 m (r = −0.75) sprint performance in female competitive sprinters. Reactive strength was assessed via 30 cm DJs with reported contact times of 0.185 s ± 0.018. Young et al. [26] also reported a significant negative relationship between reactive strength (assessed via 30 cm DJ) and acceleration over 8 m (r = −0.55) among field and court sport athletes. Contact times in the reactive strength assessment were not reported.

However, there have been some contrasting results in the literature with respect to the relationship between reactive strength and acceleration or sprinting performance. Healy et al. [27] found no relationship between RSI and sprint performance in male- and female-trained sprinters. Reactive strength was assessed across two testing protocols: 30 cm DJs with a 0.25 s contact constraint and a hopping task in which the hopping frequency was constrained to a frequency of 2.2 Hz. The constrained frequency of hopping produced GCTs of 0.157 ± 0.019 and 0.158 ± 0.015 for the male and female groups, respectively. The 30 cm DJ protocol produced contact times of 0.170 s ± 0.028 and 0.183 s ± 0.028 for the male and female groups, respectively.

Similar to Young [28], Healy et al. [27] suggested that the sprint athletes studied may have struggled to tolerate the eccentric loads during the DJ test. Healy reported a wide range of DJ contact times (men: 0.137–0.249 s; women: 0.144–0.227 s), indicating varied reactive strength capacities. Healy further argued that DJ RSI may be a poor indicator of fast SSC performance in heterogeneous groups. DJ contact times were notably longer than those observed during sprint acceleration, leading the authors to question the suitability of RSI for sprint-based assessments. The repeat hopping protocol was also considered inappropriate, as athletes appeared to limit jump height to maintain rhythm, resulting in submaximal efforts that did not reflect true impulse generation. Similarly, Young et al. [29] found no relationship between RSI and either early acceleration or maximum speed in track and field athletes, though DJ contact times were not reported. Barr and Nolte [30] also observed no association between RSI from an incremental DJ protocol (drop heights: 12–84 cm) and sprint performance over 10 m, 30 m, and 60 m in female rugby players; DJ contact times ranged from 0.30 to 0.39 s, exceeding the range typically associated with fast SSC.

The extant literature reveals that there is considerable ambiguity in the data regarding the association of reactive strength qualities with acceleration ability. Firstly, previous research utilised reactive strength assessments with contact times that were not indicative of fast SSC performance [30]. Secondly, some research included reactive strength assessments with a level of eccentric loading that was too great for the athletes’ abilities [26]. Finally, studies used acceleration split distances of too great a distance, resulting in the aggregation of multiple acceleration phases [28]. Further, it is not well established whether this relationship is stronger in early- or main-phase acceleration. To the authors’ knowledge, only one prior study [3] has directly examined the relationship between reactive strength (measured by a repeat jump test) and sprint performance, leaving the interplay between these qualities largely unexamined. That study focused solely on performance outcomes and did not consider the underlying movement patterns contributing to sprint acceleration. The present study replicates the assessment of reactive strength in relation to acceleration distances while also integrating a spatiotemporal analysis to explain how reactive strength qualities may translate into sprint mechanics. By examining kinematics, such as contact times and step lengths across early and later acceleration phases, this study provides the first comprehensive evaluation of the mechanical pathways through which reactive strength may influence sprint performance. This dual focus on outcome measures and movement mechanics advances our understanding of how fast SSC capabilities underpin acceleration ability.

The primary aim of the current study was to assess the relationship between reactive strength and sprint acceleration performance. In particular, the aim was to assess this relationship across multiple acceleration distances to understand the influence of reactive strength on discrete phases of acceleration performance. The secondary aim of the study was to investigate the possible mechanisms by which reactive strength may have a positive influence on sprint acceleration performance.

2. Materials and Methods

A cross-sectional study design was undertaken to assess the relationship between reactive strength and acceleration performance in field sport athletes. All subjects were familiarised with the 10/5 Repeated Jump Test (RJT) prior to the testing session. On the day of testing, subjects completed a general and jump warm-up, the 10/5 RJT, followed by a sprint warm-up and 3 × 30 m sprints from a standing start.

Twenty-four U21 male (age, 19.2 ± 0.8 y; height, 1.81 ± 0.05 m; and body mass, 79 ± 6.5 kg) hurling players took part in the present study. All athletes had at least six months of strength training experience. Ethical approval was provided by the institution’s Research Ethics Review Board. Additionally, athletes were informed of the benefits and risks of the investigation, and written consent forms were completed before testing in compliance with the Declaration of Helsinki.

2.1. Procedures

2.1.1. Repeated Jump Test

Subjects completed a general warm-up consisting of jogging, 10 bodyweight squats, 10 bodyweight walking lunges, 10 gluteal bridges, ankle mobility, 10 reactive ankle jumps, and 3 CMJs. For the hopping test, participants performed 1 set of the 10/5 RJT test, which was performed on an optical measuring unit (Optojump, Microgate, Bolzano, Italy) shown to have good reliability (r = 0.782, p ≤ 0.01) and is a valid measure (CV = 9%) of reactive strength [31]. The athletes performed a single CMJ and, upon landing, immediately transitioned into a series of 10 repeated bilateral jumps focusing on maximal height and minimal contact time (<0.25 s). Participants were instructed to keep their hands on their hips to ensure there was no contribution from the arms. Further instruction was given to (a) “minimise ground contact time” (b) “maximise jump height”, (c) “imagine the ground as a hot surface”, and (d) keep “legs like a stiff spring” [32]. From the ten jumps recorded, RSI was measured (jump height divided by contact time), and the five best jumps, as determined by the highest RSIs in each trial, were used to calculate average values for contact time (CT_JUMP), jump height (JH), and the reactive strength index (RSI) [24]. Jump height (JH) calculated by flight time (FT) using the Bosco method (JH = (9.81 × FT2)/8) was used in the analysis [33].

2.1.2. A 30 m Sprint Test

After a ten-minute rest, subjects then completed a sprint warm-up including 2 × 15 m standing starts. All subjects completed 3 maximal effort 30 m sprints from a standing start with six minutes of recovery between sprints. Dual-beam timing gates (Microgate, Bolzano, Italy) were positioned at 5, 10, 20, and 30 m. Split times from 0 to 5 m, 5 to 10 m, 10 to 20 m, 20 to 30 m, and, overall, 30 m were recorded. Timing was initiated at the instant the athlete’s foot left a start pad positioned underneath their rear foot, using a previously validated protocol that synchronised timing gates to the Optojump system, which is an optical measuring unit [34]. Optojump is an optical measuring unit consisting of 2 parallel bars containing LEDS; any interruptions between the bars are detected, and their durations are calculated to obtain kinematic variables such as step length, contact time (CT_SPRINT), flight time, and step frequency. Optojump has been reported to exhibit a measurement error of ±3 cm for stride length, reflecting a high level of precision in capturing spatiotemporal variables during running [35].

2.2. Statistical Analyses

Normality was assessed for all variables using the Shapiro–Wilk statistic. All variables were normally distributed (p > 0.05). Relationships between RSI and sprint times were determined by Pearson product-moment correlations (alpha ≤ 0.05) using SPSS software (version 22.0, IBM Corp, Armonk, NY, USA). The best repetitions based on 30 m sprint times were used for analysis [30]. Correlations were evaluated as small (0.1–0.3), moderate (0.3–0.5), large (0.5–0.7), very large (0.7–0.9), nearly perfect (0.9–1.0), and perfect (1.0) [36]. To determine the relationship between RSI, its derivatives, and step kinematics, two steps were taken from each sprint section and averaged for analysis. The two steps chosen were based on every player taking those two steps within the given section. Therefore, steps 2 and 3 were selected for the 0–5 m section, steps 5 and 6 for the 5–10 m section, steps 10 and 11 for the 10–20 m section and steps 15 and 16 for the 20–30 m section. Relationships between RSI and step kinematics were determined by Pearson product-moment correlations (alpha ≤ 0.05) using SPSS software (version 22.0, IBM Corp, Armonk, NY, USA). Post hoc comparisons were conducted using the Bonferroni correction to control for Type 1 error [37].

3. Results

Descriptive statistics (mean ± SD) for RSI and sprint times are presented in

Table 1. Descriptive statistics of RSI, its derivatives and sprint times and step kinematics.

Variable	Mean ± SD
RSI	1.73 ± 0.34
CTJUMP (s)	0.185 ± 0.018
Jump height (cm)	31.5 ± 4.3
0–5 m (s)	1.115 ± 0.041
5–10 m (s)	0.747 ± 0.024
10–20 m (s)	1.264 ± 0.043
20–30 m (s)	1.189 ± 0.045
0–30 m (s)	4.315 ± 0.141

. Descriptive statistics for the step kinematics for each section are detailed in

Table 2. Descriptive statistics of step kinematics for the average of the two steps in each sprint section.

Variable	Steps 2 and 3	Steps 5 and 6	Steps 10 and 11	Steps 15 and 16
Step length (cm)	130.3 ± 9.9	158.8 ± 11.2	183.4 ± 12.5	198.7 ± 14.7
Step frequency (step/s)	4.2 ± 0.4	4.4 ± 0.3	4.5 ± 0.3	4.3 ± 0.3
Velocity (m/s)	5.4 ± 0.23	6.9 ± 0.27	8.1 ± 0.3	8.6 ± 0.3
CTSPRINT (s)	0.175 ± 0.01	0.149 ± 0.01	0.134 ± 0.01	0.131 ± 0.009
Flight time (s)	0.064 ± 0.011	0.081 ± 0.012	0.092 ± 0.013	0.101 ± 0.014

. Correlations between RSI and CT_JUMP, jump height and sprint times are reported in

Table 3. Inter-correlation matrix between RSI and sprint times.

	RSI	CTJUMP	Jump Height	0–5 m	5–10 m	10–20 m	20–30 m	0–30 m
RSI	1
CTJUMP	−0.774 *	1
Jump height	0.907 *	−0.443	1
0–5 m	−0.355	0.355	−0.309	1
5–10 m	−0.539	0.638 *	−0.363	0.607	1
10–20 m	−0.576	0.517	−0.505	0.718 *	0.827 *	1
20–30 m	−0.602	0.593	−0.493	0.735 *	0.824 *	0.974 *	1
0–30 m	−0.564	0.560	−0.464	0.848 *	0.863 *	0.967 *	0.972 *	1

Results are presented with statistically significant correlations represented in bold using a Holm’s sequential Bonferroni adjusted p value (p < 0.001) *.

. Correlations between RSI and its derivatives and sprint kinematics of steps 2 and 3 are reported in

Table 4. Inter-correlation matrix between RSI and step kinematics of steps 2 and 3 (0–5 m section).

	RSI	CTJUMP	Jump Height	Step Length	Step Frequency	Velocity	CTSPRINT	Flight Time
RSI	1
CTJUMP	−0.774 *	1
Jump height	0.907 *	−0.443	1
Step length	0.182	0.062	0.281	1
Step frequency	0.117	0.248	0.030	−0.836 *	1
Velocity	0.563	−0.345	0.586	0.432	0.125	1
CTSPRINT	−0.437	0.330	0.416	0.519	−0.791 *	−0.367	1
Flight time	0.234	0.089	0.361	0.769 *	−0.757 *	0.142	0.212	1

Results are presented with statistically significant correlations represented in bold using a Holm’s sequential Bonferroni adjusted p value (p < 0.001) *.

, steps 5 and 6 in

Table 5. Inter-correlation matrix between RSI and step kinematics of steps 5 and 6 (5–10 m section).

	RSI	CTJUMP	Jump Height	Step Length	Step Frequency	Velocity	CTSPRINT	Flight Time
RSI	1
CTJUMP	−0.774 *	1
Jump height	0.907 *	−0.443	1
Step length	0.276	0.05	0.349	1
Step frequency	0.056	−0.183	−0.023	−0.831 *	1
Velocity	0.568	−0.369	0.572	0.552	0.0004	1
CTSPRINT	−0.425	0.341	−0.383	0.333	−0.524	−0.154	1
Flight time	0.258	−0.038	0.321	0.701 *	−0.749 *	0.109	−0.167	1

Results are presented with statistically significant correlations represented in bold using a Holm’s sequential Bonferroni adjusted p value (p < 0.001) *.

, steps 10 and 11 in

Table 6. Inter-correlation matrix between RSI and step kinematics of steps 10 and 11 (10–20 m section).

	RSI	CTJUMP	Jump Height	Step Length	Step Frequency	Velocity	CTSPRINT	Flight Time
RSI	1
CTJUMP	−0.774 *	1
Jump height	0.907 *	−0.443	1
Step length	0.225	−0.059	0.261	1
Step frequency	0.115	−0.221	0.048	−0.840 *	1
Velocity	0.616 *	−0.520	0.552	0.271	0.287	1
CTSPRINT	−0.459	0.468	−0.348	0.346	−0.556	0.397	1
Flight time	0.185	−0.052	0.194	0.742 *	−0.779 *	−0.067	−0.079	1

Results are presented with statistically significant correlations represented in bold using a Holm’s sequential Bonferroni adjusted p value (p < 0.001) *.

, and steps 15 and 16 in

Table 7. Inter-correlation matrix between RSI and step kinematics of steps 15 and 16 (20–30 m section).

	RSI	CTJUMP	Jump Height	Step Length	Step Frequency	Velocity	CTSPRINT	Flight Time
RSI	1
CTJUMP	−0.774 *	1
Jump height	0.907 *	−0.443	1
Step length	0.306	−0.146	0.319	1
Step frequency	−0.044	−0.087	−0.085	−0.842 *	1
Velocity	0.471	−0.406	0.425	0.383	0.17	1
CTSPRINT	−0.584	0.643 *	−0.425	0.213	−0.435	−0.331	1
Flight time	0.392	−0.277	0.344	0.804 *	−0.832 *	0.021	−0.123	1

Results are presented with statistically significant correlations represented in bold using a Holm’s sequential Bonferroni adjusted p value (p < 0.001) *.

. Large relationships were observed between RSI and 5–10 m, 10–20 m, 20–30 m, and 0–30 m times. There was a large, significant relationship between RSI and CT_SPRINT. Further, large significant relationships were observed between RSI and Velocity in the 10–20 m section and between CT_JUMP and CT_SPRINT in the 20–30 m section. Large relationships were observed between RSI and Velocity in each section. All other relationships between RSI, CT_JUMP, jump height and step length, step frequency, and flight time were small or moderate non-significant relationships.

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 Nagahara 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 sprinters 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 plantarflexor 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_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_SPRINT and CT_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).

The findings of this study contribute to the limited body of literature on the relationship between reactive strength and sprint performance in team sport athletes by identifying a clear link between RSI and CT_SPRINT. Given the large effect sizes observed in the differences between high and low RSI performers, it is plausible that improving reactive strength through specific training interventions may facilitate the enhancement of sprinting performance, particularly in athletes with poor reactive strength levels (<1.4 units).

Despite the findings, several methodological limitations must be acknowledged. One key limitation relates to the use of the bilateral 10-5 Repeated Jump Test (RJT) as the sole measure of reactive strength. While this test is commonly employed due to its practicality and reliability, it may not fully capture the specific neuromuscular demands of sprinting, which is unilateral and requires a greater horizontal force orientation. This mismatch may partly explain the absence of significant relationships between RSI and sprint performance in the 0–5 m segment. Furthermore, contradictory findings in the literature suggest inconsistencies in how reactive strength is defined and measured, with studies employing different RSI protocols (e.g., drop jumps, ankle rebound jumps, or unilateral tasks), leading to varied outcomes. For example, some studies have reported significant associations between RSI and early acceleration, particularly when unilateral or sport-specific assessments are used, challenging the notion that reactive strength is irrelevant in the initial phase of sprinting. These discrepancies highlight the need for greater standardisation in reactive strength assessment and a more nuanced understanding of how specific test modalities align with different sprint phases. Additionally, the cross-sectional nature of this study limits causal inferences, and longitudinal or intervention-based research is needed to confirm whether improvements in RSI directly translate to enhanced sprint performance across different sprint segments. Furthermore, the results cannot be generalised to other population groups, such as elite sprinters.

Given the lack of association between reactive strength, as measured by the bilateral 10-5 RJT, and 0–5 m sprint performance, subsequent studies should explore alternative assessments that exhibit greater dynamic correspondence to sprint-specific mechanics. Specifically, unilateral tests that incorporate longer GCTs, larger joint displacements, and a greater emphasis on horizontal force production may provide more valid indicators of performance in the initial steps of sprint acceleration. Moreover, the role of concentric strength and its contribution to propulsion in the early acceleration phase warrants deeper investigation, particularly through the use of task-specific assessments such as loaded sprinting, single-leg jump tasks, or horizontal force profiling. Integrating biomechanical analysis with performance testing may also help to identify the neuromuscular characteristics most predictive of acceleration ability, thereby informing more targeted training interventions.