# Biomechanical determinants of ground contact time and jump height during drop jumps in male athletes

## TL;DR

This study identifies biomechanical factors that influence jump performance in athletes, showing how different movements affect jump height and contact time.

## Contribution

The study uses PLS regression to reveal specific biomechanical determinants of jump performance in drop jumps.

## Key findings

- Greater joint range of motion and concentric impulse increase jump height but prolong ground contact time.
- Shorter ground contact time is linked to higher eccentric vertical forces and neutral hip posture.
- PLS models explained 92-93% of the variance in jump performance outcomes.

## Abstract

Drop jump (DJ) performance is underpinned by a complex interplay of biomechanical factors occurring during the eccentric and concentric phases. This study aimed to identify the biomechanical determinants of DJ performance using partial least squares (PLS) regression analysis.

Forty-three male collegiate athletes (mean age, height, and mass = 20.1 ± 1.3 years, 1.74 ± 0.07 m, 79.0 ± 23.4 kg) performed DJs from a 0.3-m box while three-dimensional kinematics and ground reaction forces (GRFs) were recorded. Ground contact time, jump height, and reactive strength index (RSI) were analyzed as outcome measures.

PLS regression models demonstrated strong explanatory power for each outcome (R2Y: 92–93%, p < 0.001). Ground contact time was negatively influenced by vertical GRFs during the eccentric phase, concentric center of mass (COM) displacement, hip abduction/adduction angle at initial ground contact, and hip and knee joint range of motion (ROM) in the sagittal planes (variable importance in projection (VIP) = 1.30–1.60, weight = −0.23 to −0.19). Jump height was positively influenced by COM displacement and work, vertical impulse and GRF, hip and knee flexion/extension ROMs during the concentric phase and knee angle at initial ground contact (VIP = 1.05–2.68, weight = 0.17–0.41). RSI was positively influenced by vertical GRF during ground contact, vertical stiffness, hip abduction/adduction ROM, concentric COM work and impulse during the concentric phase (VIP = 1.01–2.18, weight = 0.17–0.38).

These findings indicate that larger ROM and greater concentric impulse contribute to jump height but at the cost of longer ground contact, whereas shorter ground contact is promoted by high eccentric vertical ground reaction force and near-neutral hip posture, which can trade off against height.