The aim of this study was to determine the minimum playing time in matches required to produce reliable acceleration - speed (AS) profiles from global navigation satellite system (GNSS) data. The playing time of 25 professional rugby union players was recorded using GNSS technology and segmented into four sections from 40, 80, 120 and 160 minutes of play. For each interval, the impact of integrating new match data on the AS profile was assessed, aiming to identify the saturation point where additional data did not induce significant changes in the profile outputs. A repeated measures ANOVA and Bonferroni post-hoc tests were applied to examine the variations of AS profile between time intervals. This led to identify the saturation point for assessing "robust" values of theoretical maximum acceleration (A0) and maximum speed (S0). A substantial lack of significant effect was observed for A0 (p = 1.00) and S0 (p = 0.99) in the section of 160 minutes, with an intra-subject variability of 1.50 and 1.20% for A0 and S0, respectively. Determining AS profiles for rugby players is essential for monitoring performance in training and match contexts. Our findings indicate that an equivalent of two full rugby union matches is required to generate a reliable AS profile.

Rugby players must develop excellent levels of conditioning during adolescence. However, this pivotal period of life is also characterized by a surge in biological growth, which further increases the energy and nutritional requirements of this population. This study examined within-individual differences in energy intake (EI) and energy balance (EB) of 46 young rugby players during a pre-season micro-cycle. Two clusters were identified with significantly different characteristics and EB states, suggesting that young rugby players adjust their EI to match their body composition goals. The first cluster is characterized by players with a low body fat% (12.87 ± 2.53). They had a positive EB (330 ± 517 kcal), suggesting a goal of increasing muscle mass. Conversely, the second cluster is characterized by a higher body fat% (23.1 ± 1.6, p < 0.005) and reported a negative, lower EB (−683 ± 425 kcal, p < 0.005), suggesting a goal focused on reducing fat mass. Although our study provides more optimistic results than previous ones regarding the high risk of inadequate EI in young rugby players, we emphasize the importance of rigorous nutritional support, especially for players aiming to lose weight, to avoid severe caloric restriction, as well as the downstream effects of such practices on their nutritional status, given the higher risk of macro- (e.g., CHO < 6 g/kg/d) and micronutrient (e.g., iron < 11 mg/d, calcium < 1300 mg/d, vitamin D < 5 mg/d) deficiencies.

Potential estimation (PE) in rugby union traditionally emphasizes physical, anthropometric, and biological attributes to distinguish between playing positions. Forwards are typically characterized by greater strength and power, whereas backs rely more on speed and agility. However, how these differentiators evolve across developmental stages remains underexplored. This study aimed to examine age-related changes in discriminative variables influencing positional differentiation across U14, U16, and U18 categories. A total of 139 national level male rugby players were assessed: U14 (n = 64), U16 (n = 51), and U18 (n = 24). Anthropometric data (height, body mass, body mass index (BMI)), maturity status (Y-PHV, MO), sprint performance (T10, T30), and horizontal force-velocity (F- v ) profiling were collected. ANOVAs and post hoc analyses explored differences across age and position. Decision tree models identified key discriminative variables, and a feature importance analysis was performed, complemented by a recurrence analysis. Findings revealed significant age- and position-related differences (p < 0.05). BMI and maturity variables were the most relevant at U14, while sprint and F- v metrics gained importance with age. In U18, physical performance indicators such as peak power, theoretical maximal horizontal force, and slope force velocity emerged as dominant. These results suggest a transition from anthropometric to performance-based differentiation across age groups, offering key insights for refining PE strategies in youth rugby.

Purpose: Youth rugby governing bodies have progressively revised competition formats to align game demands with children's developmental characteristics. However, empirical evidence remains limited on whether these structural modifications increase children's locomotor and technical engagement during match play. This study compared locomotor intensity and technical engagement between former (old rules, OR) and revised (new rules, NR) French Rugby Federation (FFR) formats in U8 and U10 rugby players. Methods: The revised formats reduced team size from 8 vs 8 to 5 vs 5 in U8 and from 10 vs 10 to 7 vs 7 in U10, while simplifying game structure through the removal or streamlining of some set-piece situations. A total of 214 male players were monitored using 10-Hz GPS and video analysis (U8: 86 players, 45 OR/41 NR; U10: 128 players, 43 OR/94 NR). Locomotor variables included relative distance, sprint distance, maximal in-match speed, accelerations, and time in each locomotor zone, all expressed per minute of effective playing time or as a percentage thereof. Technical variables included successful and unsuccessful passes and tackles, and tries, per minute of effective playing time. Linear mixed-effects models were used. Results: In U8, NR was associated with significantly greater sprint distance per minute ( p < 0.001), higher maximal in-match speed ( p < 0.05), greater sprint time proportion ( p < 0.01), and more tries and tackles per minute ( p < 0.001) compared to OR. In U10, NR generated greater technical action frequency across most variables ( p < 0.001), while OR produced greater sprint distance per minute ( p < 0.05). Conclusions: The revised NR formats provided children with greater opportunities to move at high intensity and interact with the game, consistent with the aim of creating more age-appropriate game environments through reduced player numbers and simplified game structure.

Maviel, C, Vercruyssen, F, Duché, P, Bourdin, S, Morin, J-B, and Couderc, A. In-season individualized resisted sprint session improves in-situ acceleration-speed profile in professional rugby backs. J Strength Cond Res 40(11): 1392–1399, 2026—This study aimed to evaluate how resisted sprint training sessions with individualized load calibration influence the in-situ acceleration-speed profile in professional rugby. Recent findings highlight the importance of individualized load prescription based on the force-velocity profile and horizontal propulsive power, both closely linked to sprint performance in rugby. Two groups of professional rugby backs were examined: a control group (CG, n = 11, 2023–2024 season) and an experimental group (EG, n = 17, 2024–2025 season). The CG completed standard in-season training with no resisted sprint work, whereas the EG performed a resisted sprint protocol using the 1080 Sprint system calibrated to 50% of each player's maximal sprint velocity (S ₀ ), derived from the preintervention in-situ acceleration-speed profile. Sprint sessions were performed once per week and consisted of four 15 m resisted sprints at a constant target velocity. Significant improvements were observed in the EG for propulsive power (4.5 ± 3.0%, p < 0.001), S ₀ (2.7 ± 2.1%, p < 0.001), and maximal acceleration (1.8 ± 2.7%, p = 0.03), whereas no significant changes were found in the CG. These findings suggest that implementing individualized resisted sprint training sessions is a promising strategy to improve in-situ sprint mechanical outputs during the competitive season.