Darjan Smajla

Objectives: Evidence on the effects of curvilinear sprint (CS) training in female soccer players is limited. This study examined the effects of adding a weighted vest during CS training on sprint and vertical jump performance in youth female soccer players. Methods: Sixteen players were randomly assigned to a CS training group (CON; n = 8) or a weighted vest CS training group using 10% body mass (WV; n = 8) for six weeks (one session per week). Pre- and post-intervention testing included a 30-m linear sprint (LS), CS performed to the left and right sides, squat jump (SJ), and countermovement jump (CMJ). Peak sprinting speed (S _peak ) measured via Global Navigation Satellite System during LS, weaker-side, and stronger-side CS, as well as jump height, were analysed as primary outcomes. Curvilinear sprint asymmetry (CS _ASY ) was calculated as a secondary outcome. Results: Paired-samples t-tests showed significant improvements in weaker-side CS for CON (+3.5%) and WV (+5.3%), accompanied by significant reductions in CS _ASY . Significant decreases in SJ and CMJ height were observed only in the CON group (−7.6 and −7.7%, respectively). The ANCOVA revealed greater post-intervention S _peak in stronger-side and weaker-side CS for the WV group. Conclusion: Curvilinear sprint training improved weaker-side CS performance in youth female soccer players, whereas training with a weighted vest additionally mitigated declines in jumping performance. Curvilinear sprint training with or without a weighted vest may enhance direction-specific sprint speed in youth female soccer players.

Introduction: This exploratory study examined how eccentric braking characteristics (braking rate of force development (RFD) and braking force impulse (FI) relate to push-off force distribution and jump height during bilateral and unilateral countermovement jumps (CMJ). Methods: Data from 206 physically active individuals (basketball players and students) were retrospectively analyzed. Hierarchical multiple regression models predicted jump height, with sex and training status entered as covariates, followed by braking RFD and braking FI, and finally the early-to-late push-off FI ratio. Additional models examined whether braking variables predicted the FI ratio. Results: In bilateral CMJ, braking variables and the FI ratio significantly improved model fit beyond sex and training status, with the FI ratio emerging as a strong independent predictor of jump height (lower early-to-late push-off FI ratio: β = −0.367, p < 0.001). Braking FI was positively associated with jump height (β = 0.165, p = 0.003), and braking RFD also showed a positive independent association in the final model (β = 0.197, p < 0.001). In unilateral CMJ, the FI ratio similarly predicted jump height (lower ratio: β = −0.311, p < 0.001), whereas braking RFD was not independently associated and braking FI showed a modest positive effect (β = 0.154, p = 0.009). Braking RFD positively predicted the FI ratio in both jump tasks, indicating an association with a more early-loaded push-off profile. Conclusion: Jump height was consistently related to push-off force distribution, with relatively greater late-phase FI (i.e., a lower early-to-late ratio) associated with superior performance. Braking FI showed modest positive associations with jump height, whereas braking RFD primarily influenced push-off force distribution and displayed task-dependent relevance for performance.

This study investigated the reliability and validity of linear sprint tests (LS) and curvilinear sprint tests (CS) using a GPS device (GPEXE lt). Twenty-one (21) student athletes completed a 40 m LS as well as a left and right CS. Maximum sprint speed (MSS) and split times at short (0–10 m), intermediate (0–20 m), and long (0–30 m) distances were determined using the GPEXE lt and single-beam timing gates (TG). Intrasession reliability and concurrent validity of GPEXE lt were assessed. The GPEXE lt consistently showed high reliability for MSS (ICC ≥ 0.95; CV ≤ 1.8%), despite underestimation compared to TG (bias = −2.57 to −0.95%; ICC ≥ 0.87). Acceptable reliability was observed for CS and LS intermediate and long distance split times (ICC ≥ 0.91; CV ≤ 2.1%), with lower reliability for short distances (ICC ≥ 0.70; CV ≤ 3.6%). The GPEXE lt split times for CS and LS showed good agreement with TG (ICC ≥ 0.66), but were overestimated at long distances (5.5–9.7%) and short distances (11.1–14.6%). Although the MSS was found to be the most reliable and valid variable to assess LS and CS speed performance with GPEXE lt, caution is needed due to limited validity.

Team sports involve various sprinting actions, including curvilinear sprints, yet their neuromuscular factors have been understudied. The aim of this cross-sectional study was to investigate the relationship between lower limb muscle strength, strength asymmetries, linear sprint and curvilinear sprint performance. At two visits 12 male (age: 24.8 ± 4.7 years, height: 1.82 ± 0.06 m, body mass: 80 ± 6.58 kg) and 6 female (age: 20.8 ± 1.33 years, body height: 1.60 ± 0.02 m, body mass: 55.3 ± 2.88 kg) student-athletes completed isometric strength measurements of the knee flexors (K_F), knee extensors (K_E), hip abductors (H_ABD), hip adductors (H_ADD), as well as linear sprint and curvilinear sprint to the right and left. Sprint split times over 30 m (t₃₀) were measured and curvilinear sprint split time deficits ( t_30deficit) and inter-limb strength asymmetries were calculated. Very large negative correlations were observed between H_ADD and H_ABD strength on one side and t₃₀ of curvilinear sprint to the left ( r = −0.75 and −0.71; p < 0.001) and right ( ρ = −0.81 and −0.70; p < 0.001) on the other. The regression model consisting of H_ADD, H_ABD, and K_F explained 76% and 67% of the variance in left and right curvilinear sprint t₃₀, respectively. Similarly, 59% of the left curvilinear sprint t_30deficit variance was explained by the H_ABD and K_F strength. High inter-limb H_ABD strength symmetry was related to better left and right curvilinear sprint t₃₀ ( r = 0.71 and ρ = 0.75, p < 0.001). These results highlight the pivotal role of hip strength for curvilinear sprint speed, and emphasize the need of symmetrical H_ABD muscle strength to optimize neuromuscular function during curvilinear sprint.

Background: Strength and conditioning experts widely recognize the dynamic strength index (DSI) as a tool for assessing an athlete’s ability to utilize strength in dynamic actions. The DSI is calculated as the ratio of peak force in dynamic actions versus isometric ones. To date, the influence of fatigue on the DSI is still not fully understood. This study aimed to explore the effects of both dynamic and isometric fatigue tasks on the DSI. Methods: A total of 24 physically active participants underwent fatigue tests involving repeated countermovement jumps (dynamic) and repeated isometric mid-thigh pulls (isometric) in separate visits. Results: The results revealed a marked drop in performance, with dynamic force showing a more significant reduction (p < 0.001; d = 1.57) than isometric force (p = 0.015; d = 0.30). After the isometric fatigue task, the DSI increased, indicating a more substantial decline in isometric force (p < 0.001; d = 1.75) compared to dynamic force (p = 0.313; d = 0.08). Following this trend, the DSI decreased post-dynamic fatigue (p < 0.001; d = 0.99) and increased post-isometric fatigue (p < 0.001; d = 3.11). Conclusion: This research underscores the need to consider fatigue’s task-specific effects on the DSI, enabling more tailored training methodologies for athletes.

Jumping performance is one of the key components of volleyball game, thus evaluating jumping ability through different biomechanical variables offers opportunity for performance optimization. The aim of this study was to assess the associations between reactive strength index (RSI), reactive strength index modified (RSI_mod) and approach jump performance in male volleyball players. Forty volleyball players performed drop jump (DJ) form 40 cm high box, bilateral and unilateral countermovement jumps (CMJ) and approach jump. RSI in DJ was calculated as the ratio between jump height and ground contact time, while the RSI in CMJ tasks (RSI_mod) was calculated as ratio between jump height and jump time. Our results indicate that the relationships among different RSI variants and approach jump in volleyball players are moderate to strong (r = 0.42–0.73), with the highest correlations being observed for RSI_mod from bilateral CMJ (r = 0.676–0.727). Those observations are in line with the principle of movement specificity, which suggests that the best performance indicator should be the task that best resembles the demands of the sport-specific movements. Further research is needed to reveal more about the potential of implementing these findings for training optimization through monitoring RSI and RSI_mod values.

This study aimed to determine if there is a difference in postural stability in highly trained adolescents and young adult athletes regarding sex and sport. The participants were young athletes (n = 464) from seven different sports. We considered the center of pressure (CoP) velocity (total, anterior–posterior (AP) and medial–lateral (ML)), CoP amplitude (AP and ML), and CoP frequency (AP and ML), as assessed by single-leg quiet stance test. Significant interactions were found between sex and sport for all CoP variables (p < 0.02). Additionally, a significant main effect of sport was also found in all CoP variables (p = 0.01). Regarding sex, significant effects were found for all CoP amplitude variables (p = 0.01), as well as for CoP velocity variables, except for CoP ML (p = 0.06). Moreover, there was no sex effect for CoP frequency AP (p = 0.18). The results of the current study confirm the claim that the criteria for optimal postural strategies for elite athletes likely depend on a given sport.