Comparison of pre-contact joint kinematics and vertical impulse between vertical jump landings and step-off landings from equal heights

Although impact phase differences between vertical jump landings (VJL) and step-off landings (STL) may be related to task-specific pre-contact strategies, pre-contact mechanics are rarely examined. Thus, pre-contact kinematics and vertical ground reaction force (vGRF) impulse were examined between VJL and STL. Ten health adults (20.9 ± 1.6 yrs; 167.8 ± 4.2 cm; 68.5 ± 7.15 kg) performed 15 VJL and 15 STL from equal heights. Limb (lead; trail) by task (VJL; STL) ANOVAs (α = 0.05) compared hip, knee, and ankle joint angles 150 ms pre-contact, 100 ms pre-contact, 50 ms pre-contact, and at ground contact. Joint angular displacement was also evaluated between 150 ms pre-contact and ground contact. vGRF impulse was compared during the loading (ground contact to peak vGRF) and attenuation (peak vGRF to end of impact) phases. Greater hip flexion angles occurred during STL versus VJL at each event except 150 ms pre-contact (p ≤.004). Trail limb knee flexion angles were greater at each event when compared to the lead limb during STL (p ≤.019). Greater trail limb knee flexion angles occurred during STL versus VJL at all four events (p ≤.018), while greater plantarflexion angles occurred at all four events during VJL versus STL (p ≤.034). During STL, greater trail limb plantarflexion angles were detected at each event versus the lead limb (p <.001). Lesser hip, lead and trail limb knee displacement occurred during STL versus VJL (p <.05). Greater vGRF impulse was detected during the loading phase of VJL (<.001), while greater vGRF impulse occurred during the attenuation phase of STL (p =.025). These tasks are characterized by distinct pre-contact kinematic strategies and post-contact kinetics. The task utilized in practice should reflect the requirements of the population of interest.