The Effects of Multiple Sets of Squats and Jump Squats on Mechanical Variables.

Rossetti, ML, Munford, SN, Snyder, BW, Davis, SE, and Moir, GL. The effects of multiple sets of squats and jump squats on mechanical variables. J Strength Cond Res 34(4): 1017-1023, 2020-The mechanical responses to 2 nonballistic squat and 2 ballistic jump squat protocols performed over multiple sets were investigated. One protocol from each of the 2 nonballistic and ballistic conditions incorporated a pause between the eccentric and concentric phases of the movements in order to determine the influence of the coupling time on the mechanical variables and postactivation potentiation (PAP). Eleven men (age: 21.9 ± 1.8 years; height: 1.79 ± 0.05 m; mass: 87.0 ± 7.4 kg) attended 4 sessions where they performed multiple sets of squats and jump squats with a load equivalent to 30% 1-repetition maximum under one of the following conditions: (a) 3 × 4 repetitions of nonballistic squats (30N-B); (b) 3 × 4 repetitions of nonballistic squats with a 3-second pause between the eccentric and concentric phases of each repetition (30PN-B); (c) 3 × 4 repetitions of ballistic jump squats (30B); (d) 3 × 4 repetitions of ballistic jump squats with a 3-second pause between the eccentric and concentric phases of each repetition (30PB). Force plates were used to calculate variables including average vertical velocity, average vertical force (GRF), and average power output (PO). Vertical velocities during the ballistic conditions were significantly greater than those attained during the nonballistic conditions (mean differences: 0.21-0.25 m·s, p < 0.001, effect sizes [ES]: 1.70-1.89) as were GRFs (mean differences: 478-526 N, p < 0.001, ES: 1.61-1.63), and PO (mean differences: 711-869 W, p < 0.001, ES: 1.66-1.73). Moreover, the increase in PO across the 3 sets in 30B was significantly greater than the changes observed during 30N-B, 30PN-B, and 30PB (p ≤ 0.015). The pause reduced the mechanical variables during both the nonballistic and ballistic conditions, although the differences were not statistically significant (p > 0.05). Ballistic jump squats may be an effective exercise for developing PO given the high velocities and forces generated in these exercises. Furthermore, the completion of multiple sets of jump squats may induce PAP to enhance PO. The coupling times between the eccentric and concentric phases of the jump squats should be short in order to maximize the GRF and PO across the sets.

Assessing Plyometric Ability during Vertical Jumps Performed by Adults and Adolescents.

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 Effects of Ballistic and Nonballistic Bench Press on Mechanical Variables.

Moir, GL, Munford, SN, Moroski, LL, Davis, SE. The effects of ballistic and nonballistic bench press on mechanical variables. J Strength Cond Res 32(12): 3333-3339, 2018-The purpose of this study was to investigate the effects of ballistic and nonballistic bench press performed with loads equivalent to 30 and 90% 1 repetition maximum (1RM) on mechanical variables. Eleven resistance-trained men (age: 23.0 ± 1.4 years; mass: 98.4 ± 14.4 kg) attended 4 testing sessions where they performed one of the following sessions: (a) 3 sets of 5 nonballistic repetitions performed with a load equivalent to 30% 1RM (30N-B), (b) 3 sets of 5 ballistic repetitions performed with a load equivalent to 30% 1RM (30B), (c) 3 sets of 4 nonballistic repetitions with a load equivalent to 90% 1RM (90N-B), or (d) 3 sets of 4 ballistic repetitions with a load equivalent to 90% 1RM (90B). Force plates and a 3-dimensional motion analysis system were used to determine the velocity, force, power output (PO), and work during each repetition. The heavier loads resulted in significantly greater forces applied to the barbell (mean differences: 472-783 N, p < 0.001), but lower barbell velocities (mean differences: 0.85-1.20 m·s, p < 0.001) and PO (mean differences: 118-492 W, p ≤ 0.022). The ballistic conditions enhanced the mechanical variables only at the lower load, with 30B producing significantly greater force (mean difference: 263 N, p < 0.001), velocity (mean difference: 0.33 m·s, p < 0.001), and PO (mean difference: 335 W, p < 0.001) compared with 30N-B. Furthermore, the increase in PO across the 3 sets in 30B was significantly different from all other conditions (p = 0.013). The total mechanical work performed was significantly greater for the conditions with the heavier loads compared with those with the lighter loads (mean differences: 362-5,600 J, p < 0.001) and that performed during the ballistic conditions was significantly greater than that performed during the nonballistic conditions with the same load (mean differences: 945-1,030 J, p < 0.001). Ballistic bench press may be an effective exercise for developing PO, and multiple sets may elicit postactivation potentiation that enhances force production. However, these benefits may be negated at heavier loads.