Author(s): TOWNLEY, D., SEWRY, N., MACMILLAN, C., Institution: UNIVERSITY OF PRETORIA, Country: SOUTH AFRICA, Abstract-ID: 2354

INTRODUCTION:
The drop jump (DJ) assesses and trains neuromuscular (NM) responses in athletes. Different DJ heights can elicit distinct responses, allowing practitioners to target qualities including reactive strength, rate of force development (RFD), and eccentric load tolerance. The aim of this study was to compare force plate-derived kinetic and temporal characteristics of DJs performed from 30cm (DJ30) and 60cm (DJ60) heights to determine how DJ height influences NM behaviour.

METHODS:
29 athletes participated in two separate test sessions. Athletes performed three DJs from 30 and 60cm boxes on a force plate. Data was processed using VALD Performance Pty Ltd software. The best trial was used (i.e., the trial with the lowest values for temporal parameters and the highest values for the other variables). Paired sample t-tests and effect sizes (ES) were used to analyse primary force-plate variables (reactive strength index (RSI), contact time, and peak drop landing force). Secondary outcomes, which included peak power, active stiffness, peak velocity and vertical velocity at take-off, jump height, concentric and eccentric force, impulse, and drop-landing RFD, were also analysed using paired t-tests with p-values adjusted using the Benjamin-Hochberg false discovery rate (FDR) procedure (q<0.05). All force-related variables (peak power, eccentric and concentric force and impulse, peak drop landing force and active stiffness) were normalised to body mass.

RESULTS:
DJ30 emphasised statistically significant concentric performance, i.e., increased take-off velocity (DJ30=2.61 ± 0.39, DJ60=2.21 ± 0.61m·s⁻¹), peak velocity (DJ30=2.73 ± 0.38, DJ60=2.33 ± 0.61m·s⁻¹), impulse (DJ30=2.59 ± 0.37, DJ60=2.18 ± 0.60N·s·kg⁻¹), mean concentric force (DJ30=29.87 ± 4.89, DJ60=27.62 ± 4.65N·kg⁻¹), active stiffness (DJ30=357.35 ± 163.59, DJ60=216.14 ± 98.92N·m·kg⁻¹), and jump height (DJ30=35.62 ± 10.4, DJ60=26.74 ± 14.73cm) (all p<0.001, ES=0.76-1.17). Whereas, DJ60 imposed significantly greater eccentric/landing demands, evidenced by higher mean eccentric force (DJ30=34.95 ± 6.80, DJ60=41.37 ± 7.94N·kg⁻¹), impulse (DJ30=2.43 ± 0.01, DJ60=3.69 ± 0.45N·s·kg⁻¹) and peak power (DJ30=169.42 ± 38.28, DJ60=202.68 ± 48.02W·kg⁻¹) (all p<0.001, ES=0.94-2.31). For primary variables, DJ60 contact time was longer (DJ60=0.31 ± 0.08, DJ30=0.27 ± 0.07s; p<0.001; d=0.95). Peak drop landing force was greater at DJ60 (DJ60=130.41 ± 38.36, DJ30=82.86 ± 28.98N·kg⁻¹; p<0.001; d=1.43). RSI showed no significant difference (DJ30=2.39 ± 0.65, DJ60=2.31 ± 0.59; p=0.127; d=0.29). Following FDR correction, all secondary variables remained statistically significant except for drop landing RFD (p=0.071).

CONCLUSION:
Altering DJ height significantly changes NM demands, with DJ30 enhancing concentric characteristics and DJ60 imposing greater eccentric and landing loads and neither improving reactive efficiency. The results highlight the importance of height-specific prescription when using DJs to elicit targeted NM responses.