Purpose: The mechanical responses to two non-ballistic squat and two ballistic jump squat protocols performed over multiple sets were investigated. One protocol from each of the two non-ballistic 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 post-activation potentiation (PAP).
Methods: Eleven men (age: 21.9 +/- 1.8 years; height: 1.79 +/- 0.05 m; mass: 87.0 +/- 7.4 kg) attended four sessions 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) 3 x 4 repetitions of non-ballistic squats (30N-B); 2) 3 x 4 repetitions of non-ballistic squats with a 3-second pause between the eccentric and concentric phases of each repetition (30PN-B); 3) 3 x 4 repetitions of ballistic jump squats (30B); 4) 3 x 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).
Results: Vertical velocities during the ballistic conditions were significantly greater than those attained during the non-ballistic 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 three 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 non-ballistic and ballistic conditions, although the differences were not statistically significant (p>0.05).
Conclusion: 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.
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