Purpose: To quantify the acute effects of a spectrum of eccentric load reductions on neuromechanical adjustments during the performance of weighted jump squats (WJSs).
Methods: On separate days, 16 well-trained participants performed WJS trials with various eccentric load reductions (0% [body mass only], 25%, 50%, 75%, and 100% [standard WJS] of concentric load) with a mechanical braking unit, while concentric load was set at 30% of peak isometric squat force in all trials. A force platform and a motion-capture system were used to assess neuromuscular performance.
Results: Peak power output was 6.2% (4.7%) higher when load was reduced by 50% versus 0% (55.4 [7.8] vs 51.9 [7.6] W/kg; P = .001). Compared with no braking (0.326 [0.059] m), jump height was ∼13% to 17% higher for all eccentric load reduction conditions (all P < .001). Vertical ground reaction forces were progressively lower for 25%, 50%, 75%, and 100% loading conditions (-22.1% [14.6%], -32.3% [10.8%], -42.0% [13.2%], and -46.1% [14.7%]; all P ≤ .001) in reference to body mass only.
Conclusion: Eccentric load reduction is advantageous compared with traditional isoinertial loading for improving both jump height and peak power output during the concentric portion of maximal-effort WJS. This practice also decreases mechanical constraints in the lower extremities, which may become beneficial for load-compromised individuals.
Keywords: ballistic exercise; landing impact; optimal load; plyometrics; stretch-shortening cycle.