For years, inter-limb asymmetry data have been reported in performance science and injury rehabilitation literature, together with routine monitoring in professional practice. Intuitively, many practitioners are almost 'hard-wired' to think that if a sizable inter-limb asymmetry presents itself, then something must be done to correct it. However, before any attempt is considered regarding trying to alter the magnitude of asymmetry, practitioners and researchers should first better comprehend the associated challenges and pitfalls of inter-limb asymmetry data. Once these are understood, a series of robust and pragmatic principles are proposed to enhance the utility of asymmetry data, which in turn, should help ensure that appropriate due-diligence is undertaken, serving to guide subsequent decision-making when considering this metric.
This study aimed to compare maximum acceleration and speed capabilities in professional soccer players, both derived from the acceleration-speed (AS) profile (theoretical maximum acceleration [A0] and speed [S0]) and direct assessment (maximum acceleration [MaxAcc] and speed [MaxSpeed]), according to both (i) sex and the sports level, and (ii) the playing position. A total of 737 professional women and men soccer players were monitored during 5-10 official matches. Data were collected using 18-Hz GPS devices to derive AS profiles and directly measure acceleration and speed output. Across all playing levels, professional men soccer players demonstrated significantly (p < 0.01) higher values than female players for A0 (d = 1.14-1.87), S0 (d = 3.88-4.82), MaxAcc (d = 0.57-1.22), and MaxSpeed (d = 2.46-2.81). Likewise, players of higher sports levels showed superior output than their lower counterparts (First Men's Division > Second Men's Division > Under 20 Men's Division; p < 0.05). Position-specific analysis revealed that midfielders had significantly (p < 0.05) lower MaxSpeed values than other positions such as full-backs (d = 0.63-1.17), wide midfielders (d = 0.82), and forwards (d = 0.67-1.06) in both the First and Second Divisions. Conversely, wide midfielders in the Under 20 Men's Division exhibited significantly (p < 0.05) higher A0 values than central defenders (d = 0.78). These findings highlight the importance of conducting sex- and position-specific analyses of the AS profile to effectively monitor acceleration and speed capacities across different sports levels in professional soccer.
This study investigated how pitch size and a task type (position vs. possession games) influence running demands and external load across player positions in soccer training. Twenty-five young professional soccer players (21.9 ± 1.9 years) participated in 36 training sessions during the 2021-2022 season. Position and possession games were conducted on three pitch sizes (small, medium, large). Players wore GPS devices to measure total distance covered (DC), peak speed, and acceleration/deceleration metrics (low-intensity < ±3 m•s⁻2 and high-intensity > ±3 m•s⁻2). Mixed models assessed the effects of pitch size and a task type on these metrics and positional differences. Possession games elicited higher total DC than position games across all sizes studied (p < 0.005). In the large format, the peak speed was higher in possession than in position games (p < 0.001). On small pitches, possession games resulted in greater low-intensity accelerations/decelerations (ACC<3/DEC<3), but fewer high-intensity accelerations/decelerations (ACC>3/DEC>3) and maximal deceleration compared to position games (p < 0.05). Positional analysis revealed that central defenders and fullbacks reached greater total DC across all three formats of possession games (p < 0.05). Central-midfielders and forwards recorded higher peak speeds in the large possession game (p ≤ 0.01). Wide-midfielders achieved fewer ACC<3 and DEC<3 events in position games during the small format, while fullbacks performed fewer ACC<3 but more ACC>3 in the same format during position games (p ≤ 0.05). Field size and the game format significantly affect external load in soccer. Possession games require greater total DC regardless of size and higher peak speeds on larger fields, while position games involve more high-intensity actions, reflecting players' tactical roles.
This study investigated the effects of static stretching (SS) and its combination with menthol gel on lower limb muscle activation, synergistic patterns, and squat jump (SJ) performance at two knee starting angles (90° and 120°). Twelve participants completed a randomized crossover protocol across three sessions, each involving SJ trials under different intervention conditions. Data were collected via a 3D motion capture system, EMG, and a force plate. EMG data were analyzed using principal component analysis and amplitude calculations, while jump height, ground contact time, peak ground reaction force (GRFpeak), and the rate of force development (RFD) were derived from kinematic and kinetic data. Results showed no significant changes in average EMG amplitude with SS or menthol gel (p > 0.05). However, SS at 120° significantly altered muscle synergy (p < 0.001, d = 2.02), increased jump height (p = 0.002, d = 0.59), and reduced ground contact time (p = 0.005, d = 1.15), GRFpeak (p < 0.001, d = 1.59), and the RFD (p < 0.001, d = 1.47). Menthol gel offset these changes. Additionally, joint angle influenced all performance metrics (p < 0.05). These findings suggest that while SS can enhance jump height at certain joint angles, it may hinder explosive force output, and combining it with menthol gel can mitigate such drawbacks.
The present study explored whether incorporating run-specific isometric exercises (RSIso) into a complex training (CT) routine would provide additional benefits for youth soccer players during the in-season. Twenty-four male athletes (aged 18–19 years) were randomly divided into two groups: one following a conventional CT program and the other performing an identical program preceded by isometric conditioning training (IST-CT). Both interventions were carried out twice per week for eight weeks, with equivalent training volume and intensity. Performance outcomes were assessed through countermovement jump, drop jump, broad jump (BJ), 30-m linear sprint, and the 5-0-5 change-of-direction (COD) tests. Two-way mixed-design ANOVA (between-subjects factor: group [IST-CT vs. CT]; within-subject factor: time [pre vs. post]) revealed significant main effects of time for COD ability with the non-dominant leg (p = 0.01). Significant group × time interactions were observed for peak power (p = 0.01) and BJ performance (p = 0.03), yet post-hoc comparisons did not confirm statistically meaningful differences (all p > 0.05). Overall, both training approaches led to comparable adaptations in strength-speed performance. Although the direction of changes tended to favor the IST-CT condition, the modest magnitude of effects does not allow to draw definitive conclusions regarding its superiority over conventional CT, indicating that further research is required to confirm the practical relevance of these findings.
