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.
The increase in the competitive level and popularity of handball necessitates the optimization of training methods, particularly in the development of explosive strength, which determines jump effectiveness and overall game performance. This study analyzed the impact of specific power training and conventional resistance training on jumping abilities of young handball players. A total of 48 athletes were selected for the experiment and randomly assigned to a power training (PT) group, a resistance training (RT) group, or a control (C) group. The training program included plyometric exercises, dynamic neuromuscular activations, and reaction-time-based stimuli, with their effects evaluated through vertical jump tests (CMJ and SJ). The results indicated significant increases in jump height, maximum power, and relative maximum power in the PT group (p < 0.05), suggesting that specific power training more effectively supported the development of dynamic variables than standard resistance training methods. While the RT group demonstrated gains in strength, the corresponding improvements in vertical jump performance were modest and not as substantial as those seen in the power training group. The findings highlight the crucial role of neuromuscular mechanisms in generating explosive power, as well as the importance of training methods based on the stretch-shortening cycle.
Precise timing of ball-racket contact is a critical determinant of stroke performance in tennis, yet few studies have objectively quantified this variable across different players’ groups. This study developed and validated a hybrid vision-based framework combining K-nearest neighbors (KNN) background subtraction with Hue-Saturation-Value (HSV) color segmentation to analyze the spatial relationship between the contact point and the apex of the ball’s trajectory. Twelve participants were recruited and stratified by skill level and gender, each performing 30 forehand and 30 backhand strokes, yielding 720 stroke events. Contact point overlap ratios and vertical height distributions were extracted, and two-way ANOVA was used to examine main and interaction effects. Results indicated a significant effect of the skill level, with top-level players demonstrating higher overlap ratios and reduced vertical deviations compared to average-level players (p < 0.001, partial η² = 0.386). Gender differences were negligible among top-level players but pronounced in the average-level group, particularly for backhand strokes (p < 0.001). These findings highlight the skill level as the dominant factor influencing contact point precision, while gender disparities emerge primarily among less experienced athletes. The proposed computer vision approach offers a low-cost and scalable tool for objective stroke assessment and has potential applications in individualized training feedback and performance monitoring.
