Changes in body composition and physical performance measures during a regular competitive season among young backs and forwards rugby players.

This study aimed to compare the changes in body composition and physical qualities of under 19's backs and forwards during the season (i.e. from pre-season [Pre-S] to end-season [End-S]). Twenty-seven male youth rugby union players (mean ± SD: age, Forwards [n = 11]: 17.5 ± 1.2 and Backs [n = 16]: 17.0 ± 0.9 years) participated in this study. Participants were tested twice (i.e. at Pre-S and End-S) and completed: anthropometric, body composition, countermovement and squat jumps, 30-m sprint, squat and bench press 1-repetition maximum (SQ-1RM and BP-1RM). Significant differences were observed between Pre-S and End-S for body mass (BM) and lean mass (LM), among both playing positions (p < 0.034; ES > 0.71), whereas all other variables remained unchanged. Regarding physical performance, backs and forwards showed greater SQ-1RM and BP-1RM, respectively (p < 0.043; ES>-0.69). Moreover, backs and forwards exhibited higher split times from 5 to 30 m (p: 0.013 to <0.001). Substantial increases were observed in BM and LM for backs and forwards, which may have negatively impacted acceleration (i.e. 5-m sprint time) and initial sprint momentum for both playing positions. Our findings highlight the importance of carefully balancing changes in BM and body composition, to avoiding the detrimental effects of these variations on sprint performance.

Relación de la coordinación motriz, edad y sexo con la fuerza y agilidad en escolares / Relationship between motor coordination, age and sex with strength and agility in schoolchildren

El objetivo principal fue analizar el efecto de la coordinación motriz, la edad y el sexo sobre la fuerza y agilidad en escolares de 6-11 años. En el estudio participaron 647 escolares de dos centros de educación Primaria (381 niños y 266 niñas). Se ha realizado un análisis de correlación de Pearson para estudiar la relación entre la edad y la coordinación motriz (medida a través del test 3JS) sobre la fuerza (salto horizontal y salto con contramovimiento) y la agilidad (medida a través del test 4x10). Las diferencias relacionadas con el sexo se analizaron a través del test t-Student y la U de Mann-Whitney, dependiendo de si las variables siguen una distribución normal. Se ha aplicado un modelo ANCOVA donde las variables dependientes son el salto horizontal, el salto con contramovimiento y el 4x10, el factor es la variable sexo y las covariables son la coordinación motriz y la edad. Los resultados han mostrado una asociación positiva entre la coordinación motriz y las pruebas utilizadas para valorar la fuerza y la agilidad. La variable sexo tiene una relación significativa con el salto horizontal, salto con contra movimiento y el 4x10. Tras el análisis según modelo ANCOVA realizado en este estudio, la variable sexo influye sobre el salto horizontal y sobre la agilidad, pero no sobre el salto con contramovimiento cuando se elimina el efecto de la coordinación motriz y de la edad de los escolares. (AU)

The aim of this study is to delve into the effect that motor coordination, age and gender have on strength and agility in Primary stage, specifically in students aged 6 to 11 years. 647 schoolchildren from two primary education centers (381 boys and 266 girls) participated in this study. A Pearson correlation analysis has been carried out to study the relationship between age and Motor Coordination (measured through/by the 3JS test) on strength tests (horizontal jump with feet together and jump with counter movement) and agility (measured through/by the 4x10 test). Subsequently, the gender differences in these variables have been studied using the Student's t test or the Mann-Whitney U test, depending on whether the variables follow a normal distribution. Finally, to delve into the objective of the research, an ANCOVA model has been applied where the dependent variables are the horizontal jump, the counter-movement jump and the 4x10, the factor is the gender variable and the covariates are Motor Coordination and age. The results have shown a positive association between the Motor Coordination and the tests used to assess strength and agility. The gender variable has a significant relationship with the horizontal jump, the counter movement jump and the 4x10. After the analysis according to the ANCOVA model carried out in this study, the gender variable influences the horizontal jump and agility, but not the counter-movement jump when the effect of motor coordination and the age of the schoolchildren is eliminated. (AU)

Muscle Activity, Leg Stiffness, and Kinematics During Unresisted and Resisted Sprinting Conditions.

ABSTRACT: Zabaloy, S, Carlos-Vivas, J, Freitas, TT, Pareja-Blanco, F, Loturco, I, Comyns, T, Gálvez-González, J, and Alcaraz, PE. Muscle activity, leg stiffness and kinematics during unresisted and resisted sprinting conditions. J Strength Cond Res 36(7): 1839-1846, 2022-This study aimed to compare muscle activity, leg stiffness, and kinematics (contact and flight time [FT], stride length and frequency, and trunk angle [TA]) of unloaded sprinting to resisted sprint (RST) using different loads. Twelve male rugby players (age: 23.5 ± 5.1 years; height: 1.79 ± 0.04 m; body mass 82.5 ± 13.1 kg) performed 30-m sprints using different loading conditions (0, 10, 30 and 50% of velocity loss-Vloss-from the maximum velocity reached under unloaded condition). Muscle activity from 4 muscles (biceps femoris long head, rectus femoris [RF], gluteus medius and gastrocnemius), leg stiffness (Kleg), and kinematics were measured during the acceleration and maximum velocity (Vmax) phases of each sprint. Heavier loads led to significantly lower biceps femoris long head activation and higher rectus femoris activity (p < 0.01-0.05). Significant reductions in Kleg were observed as loading increased (p < 0.001-0.05). Kinematic variables showed substantial changes with higher loads during the acceleration and Vmax phase. In conclusion, the heavier the sled load, the higher the disruptions in muscle activity, Kleg, and kinematics. When coaches and practitioners intend to conduct resisted sprint training sessions without provoking great disruptions in sprint technique, very-heavy sled loads (greater than 30% Vloss) should be avoided. However, heavy sled loads may allow athletes to keep specific positions of the early acceleration phase for longer time intervals (i.e., first 2-3 strides during unresisted sprints).

Estimation of maximum sprinting speed with timing gates: greater accuracy of 5-m split times compared to 10-m splits.

This study assessed the validity of 5-m (TG5) and 10-m (TG10) split times measured with timing gates to estimate maximum sprint speed (MSS) against a criterion measure radar gun (RG) during the maximum velocity phase of a 30-m sprint. Nineteen amateur rugby players performed two 30-m sprints. The timing gates were placed at the starting line and at 5-, 10-, 20-, 25- and 30-m. In addition, a RG was used to measure instantaneous velocity. Both trials per participant were used selected as references. MSS obtained from TG10, TG5 and RG showed high intraclass correlation coefficients (0.971-0.978), low coefficients of variation (1.14-1.70%) and smallest detectable changes (<0.02 m/s). Pairwise comparison revealed differences (p = 0.002) in MSS when comparing TG10 to RG, but not TG5 and RG (p = 0.957). Almost perfect correlations were found between RG, TG5 and TG10 (r > 0.926, p < 0.001). In conclusion, MSS obtained from TG5, TG10 and RG presented good intra-session reliability. However, practitioners should be aware that substantial differences exist between TG10 and RG. For the assessment of MSS in team-sport athletes, it is recommended the use of TG5 for more accurate estimations when a gold standard criterion is not available.

Relationships between Resisted Sprint Performance and Different Strength and Power Measures in Rugby Players.

This study aimed to investigate the relationship between a specific isometric-strength sprint test (SIST) and unresisted maximum velocity (Vmax), sprint times across different loading conditions, and the velocity loss (Vloss) loads required to achieve each intended Vloss condition during resisted sprint training (RST) in rugby players. Additionally, the investigation examined the relationship between strength in the back-squat one-repetition maximum (1RM-SQ) as well as isometric squat (ISQT), jumps, and sprint performance variables. Twenty (n = 20) male amateur rugby players performed, on two separate occasions, a structural multiple-joint assessment of jumps, strength, and sprint performance. Interestingly, SIST revealed moderate correlations (r = 0.453 to 0.681; p < 0.05) between 1RM-SQ and ISQT. The SISTrel (relative to body mass), but not SIST, used in the present study showed moderate correlations (r = 0.508 to 0.675; p < 0.05) with the loads needed to reach 10%, 30%, and 50% of Vloss during RST. The SISTrel that measures resultant force application in a more sprint-related position explains much of the individual response of each athlete during sprinting towing a sled and can also be used to prescribe and quantify loads in the RST in a more objective and individual manner.