DESPITE STRONG THEORETICAL EVIDENCE, THE EFFECTIVENESS OF RESISTANCE TRAINING METHODS ON SPRINTING PERFORMANCE IS NOT ALWAYS DEMONSTRATED EXPERIMENTALLY. ACCELERATIVE SPRINTING IS LIMITED BY THE REQUIREMENT OF A FORWARD-DIRECTED GROUND REACTION FORCE DURING PROGRESSIVELY SHORTER STANCE PHASES THAT ACCOMPANY HIGHER SPRINTING SPEEDS, WHEREAS MAXIMAL SPEED SPRINTING IS LIMITED BY THE APPLICATION OF SUFFICIENT VERTICAL IMPULSE DURING STANCE, CONSTRAINING MINIMAL STANCE DURATIONS. CONSIDERING THE MECHANICAL LIMITATIONS AND THE BIOMECHANICAL SOLUTIONS USED BY THE FASTEST SPRINTERS FROM A CONSTRAINTS-LED PERSPECTIVE PROVIDES A FRAMEWORK FROM WHICH PRACTITIONERS CAN EXPLORE THE INCORPORATION OF RESISTANCE AND SPRINT TRAINING IN THE DEVELOPMENT OF LONG-TERM TRAINING PROGRAMS.

The purpose of this study was to compare different methods for assessing plyometric ability during countermovement (CMJ) and drop jumps (DJ) in a group of adults and adolescents. Ten resistance-trained adult men (age: 22.6 ± 1.6 years) and ten adolescent male basketball players (age: 16.5 ± 0.7 years) performed a CMJ and a DJ from a height of 0.40 m. Jump height (JH), contact time, normalized work (WNORM), and power output (PONORM) during the absorption and propulsion phases were calculated from force platforms and 3-D motion analysis data. Plyometric ability was assessed using the modified reactive strength index (RSIMOD during CMJ) and the reactive strength index (RSI during DJ) as well as three indices using propulsion time, propulsion work (PWI), and propulsion power. Adults jumped significantly higher than adolescents (mean difference [MD]: 0.05 m) while JH (MD: 0.05 m) and ground contact time (MD: 0.29 s) decreased significantly from CMJ to DJ. WNORM (MD: 4.2 J/kg) and PONORM (MD: 24.2 W/kg) during the absorption phase of CMJ were significantly less than these variables during the propulsion phases of the jumps. The reactive strength index variants increased significantly from the CMJ to DJ (MD: 0.23) while all other plyometric indices decreased significantly. Neither RSIMOD nor RSI contributed significantly to the prediction of JH during CMJ and DJ, respectively, while PWI was able to explain ≥68% of the variance in JH. Variants of the reactive strength index do not reflect the changes in mechanical variables during the ground contact phase of CMJ and DJ and may not provide an accurate assessment of plyometric ability during different vertical jumps.

The purpose of this study was to investigate the eccentric and concentric force-velocity (Fv) characteristics recorded during drop jumps (DJ) from different heights and loaded jump squats (JS) and to determine the number of jumps required to accurately model the eccentric and concentric Fv relationships. Fourteen resistance-trained men (age: 21.9 ± 1.8 years) performed a countermovement jump (CMJ) and DJ from heights of 0.40, 0.60, and 0.80 m. JS with loads equivalent to 0%, 27%, 56%, and 85% 1-repetition maximum were performed in a separate session. Force platforms and a 3-D motion analysis system were used to record the average force (F¯) and velocity (v¯) during the absorption (CMJ, DJ40, DJ60, DJ80) and propulsion (JS0, JS27, JS56, JS85) phases of the jumps. Eccentric (absorption phase) and concentric (propulsion phase) Fv characteristics were then calculated and linear regression equations were determined when the number of jumps included was varied. F¯ during the absorption phase significantly increased from CMJ to DJ60 while v¯ increased significantly from CMJ to DJ80. The two-point method (CMJ, DJ80) resulted in a significantly lower y-intercept (mean difference [MD]: 0.7 N/kg) and a greater slope (MD: 0.7 Ns/m) for the eccentric Fv characteristics compared to the multiple-point method. F¯ increased significantly and v¯ decreased significantly with increasing external load in the JS conditions. The two-point method (JS0, JS85) resulted in a significantly greater y-intercept (MD: 1.1 N/kg) compared to the multiple-point method for the concentric Fv characteristics. Both DJ and loaded JS may provide means of assessing the eccentric and concentric Fv characteristics with only two jumps being required.

PURPOSE:To investigate the effects of two non-ballistic squat and two ballistic jump squat protocols performed over multiple sets on mechanical variables. METHODS: In a counterbalanced cross-over design, 11 resistance-trained men (age: 21.9 ± 1.8 years; height: 1.79 ± 0.05 m; mass: 87.0 ± 7.4 kg) attended four testing sessions during a three week period where they performed multiple sets of squats and jump squats with a load equivalent to 30% 1-repeititon maximum under one of the following conditions: 1) three sets of four non-ballistic repetitions (30N-B), 2) three sets of four non-ballistic repetitions with a 3-second pause between the eccentric and concentric phases (30PN-B), 3) three sets of four ballistic repetitions (30B), 4) three sets of four ballistic repetitions with a 3-second pause between the eccentric and concentric phases (30PB). Force plates and a 3-D motion analysis system were used to determine the mean vertical velocity, mean vertical force, and mean power output during each repetition.

Moir, GL, Munford, SN, Snyder, BW, and Davis, SE. Mechanical differences between adolescents and adults during two landing phases of a drop jump task. J Strength Cond Res 36(4): 1090–1098, 2022—The mechanical differences between the first and second landing phases of a drop jump (DJ) task performed by adolescent and adult male players were investigated. Eleven adolescent basketball players (age: 16.5 ± 0.7 years) and 11 resistance-trained adults (age: 22.3 ± 1.9 years) performed DJs from a height of 0.40 m. Force plates and a 3-dimensional motion analysis system were used to determine mechanical variables, including landing velocity, normalized vertical stiffness, normalized peak impact force, and work as well as mechanical characteristics of the hip, knee, and ankle joints during the absorption phase of each landing. The adolescents produced greater peak impact forces (mean difference [x¯Diff] = 42 N·kg0.67; effect size [ES] = 1.15) and vertical stiffness (x¯Diff = 126 N·kg0.67·m−1; ES = 1.28) during shorter absorption phases (x¯Diff = 0.09 seconds; ES = 2.67) compared with the adults, despite their lower landing velocities (x¯Diff = 0.21 m·s−1; ES = 1.37). Furthermore, the adolescents generated greater peak extensor joint moments at the lower-body joints compared with the adults (x¯Diff = 2.3 N·m·kg0.67; ES = 1.17), but they did not effectively modulate the energy absorbed by the joint moments in response to the changing demands of the landing tasks. The assessment of the biomechanical characteristics of the 2 landing phases associated with a DJ task revealed that adolescent male basketball players adopt neuromuscular strategies that may increase the risk of incurring musculoskeletal injuries compared with resistance-trained adults.