This study aimed to identify attributes that discriminate selected from non-selected players and predict selection into a rugby league development programme in older adolescent players. Anthropometric, performance and psychological attributes were measured in under-16 (N = 100) and under-18 (N = 60) rugby league players trialling for selection into a development programme with a professional Australian club. Sprint times (P < 0.001), predicted VO (P = 0.002) and push-ups (P = 0.004) were superior in selected under-16 players, and sprint times (P ≤ 0.045), push-ups (P< 0.001) and chin-ups (P = 0.013) were superior in selected under-18 players. Further, 10-m sprint (β = -7.706, standard error [SE] = 2.412), VO (β = 0.168, SE = 0.052) and body mass (β = 0.071, SE = 0.023) significantly predicted selection (R = 0.339) in under-16 players, while push-ups (β = 0.564, SE = 0.250), 10-m sprint (β = -68.477, SE = 28.107), body mass (β = 0.360, SE = 0.155) and chronological age (β = -3.577, SE = 1.720) significantly predicted selection (R = 0.894) in under-18 players. These findings emphasise the importance of performance attributes in junior rugby league and indicate talent identification test batteries should be age-specific in older adolescent players.

Purpose: This study aimed to identify the relationships between lower limb muscle characteristics and mechanical variables derived from the vertical (jumping) and horizontal (sprinting) forcevelocity-power (FVP) profiles. Methods: Nineteen subelite male rugby league players performed a series of squat jumps and linear 30-m sprints to derive the vertical and horizontal FVP profiles, respectively. The theoretical maximal force (F 0 ), velocity (V 0 ), and power (P max ) were derived from both the vertical (i.e., vF 0 , vV 0 , and vP max ) and the horizontal (i.e., hF 0 , hV 0 , and hP max ) FVP profiles. Vastus lateralis (VL), biceps femoris long head, and gastrocnemius medialis (GM) and lateralis muscle fascicle length, pennation angle, and thickness were measured using B-mode ultrasonography. Magnetic resonance imaging was used to calculate volumes of major lower limb muscles, whereas proton magnetic resonance spectroscopy was used to quantify the carnosine content of the GM to estimate muscle fiber typology. Results: Variation in vP max was best explained by GM muscle fiber typology (i.e., greater estimated proportion of Type II fibers) and VL volume (adjusted r 2 = 0.440, P = 0.006), whereas adductor and vastus medialis volume and GM muscle fiber typology explained the most variation in hP max (adjusted r 2 = 0.634, P = 0.032). Rectus femoris and VL volume explained variation in vF 0 (r 2 = 0.430, P = 0.008), whereas adductor and vastus medialis volume explained variation in hF 0 (r 2 = 0.432, P = 0.007). Variations in vV 0 and hV 0 were best explained by GM muscle fiber typology (adjusted r 2 = 0.580, P < 0.001) and GM muscle fiber typology and biceps femoris short head volume (adjusted r 2 = 0.590, P < 0.001), respectively. Conclusion: Muscle fiber typology and muscle volume are strong determinants of maximal muscle power in jumping and sprinting by influencing the velocity-and force-oriented mechanical variables.

Tredrea, MSJ, Middleton, KJ, Bourne, MN, Carey, DL, Scanlan, AT, and Dascombe, BJ. Load centralization does not affect the kinetic and kinematic output of countermovement jumps. J Strength Cond Res 36(4): 1084–1089, 2022—This study aimed to compare the kinetics, kinematics, and performance of countermovement jumps (CMJs) when completed with 2 different loading conditions (centralized or peripheral) across increasing loads. Seventeen subjects (12 men and 5 women) randomly completed 2 series of CMJs with increasing loads separated by a 30-minute rest period between conditions. Subjects were loaded with either a weighted vest (centralized) or straight barbell (peripheral). A randomized, counterbalanced crossover design was used with incremental loads of 10, 20, 30, 40, and 50% of body mass added to the vest or barbell. Measures of peak force, acceleration, velocity, and power were calculated across each subphase of the CMJs. No significant differences were observed in kinetic or kinematic variables between loading conditions. Within each condition there were significant reductions (p < 0.05) in peak concentric velocity and acceleration, as well as significant increases (p < 0.05) in peak force when the external load increased. Furthermore, braking and propulsive phase duration significantly increased (p < 0.05) and jump height significantly decreased (p < 0.05) as the external load increased. Countermovement jump performance was similar in both central and peripheral loading, whereas increasing load significantly affected jump height, force, velocity, and acceleration variables irrespective of load position. The training stimulus from an external load placed centrally or peripherally is similar regardless of where it is positioned; however, from a practical perspective, a weighted vest may provide a more mobile and safer alternative than a barbell.

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