Differences In Impact Force Attenuation And Knee Kinematics During Drop Jump And Drop Landing

Abstract

Few studies have compared impact attenuation during a pure landing task when impact attenuation is the main goal to a drop jump task where impact attenuation is immediately followed by energy generation. PURPOSE: To examine differences of impact force attenuation between drop landing and the landing phase of a drop jump activity. METHODS: Seven NCAA football athletes (TRAINED) and 7 recreationally active students (REC) with limited sports training and prior experience in jumping sports, performed 5 drop landing trials from each of 3 landing heights: 40 cm, 60 cm and 100% of each individual's maximum jump height (100%MJH) and 5 drop jump trials from each of the 3 drop heights. Simultaneous recording of 3D kinematics and ground reaction force (GRF) were conducted at 240 Hz and 1200 Hz, respectively. Selected peak GRF and kinematic variables were evaluated using a mixed design 2 × 2 (group x height) repeated measures analysis of variance (ANOVA, p < 0.05) for the 40 and 60 cm conditions for the two activities separately. The group differences at the 100%MJH were evaluated with an independent-samples t-test. RESULTS: The results showed that the TRAINED participants had significantly smaller peak GRF (1.7 and 2.2 BW for 40 and 60 cm) and longer time to the peak (0.057 and 0.053 s for 40 and 60 cm) compared to the REC participants (2.0 and 2.7 BW, 0.050 and 0.048 s for 40 and 60 cm) in the landing phase of drop jump. However, the TRAINED participants had greater peak GRFs (2.7 and 3.5 BW for 40 and 60 cm) and significantly shorter times to the peak (0.048 and 0.043 s for 40 and 60 cm) compared to the REC participants (2.0 and 2.7 BW, 0.060 and 0.053 s for 40 and 60 cm) in drop landing. The TRAINED athletes also showed similar knee ranges of motion (ROM) in the landing phase during drop jump but smaller and non-significant knee ROMs (p = 0.051) in drop landing compared to the REC counterparts. CONCLUSIONS: The TRAINED athletes exhibited greater impact attenuation during the landing phase of drop jump but less impact attenuation during drop landing. This difference is related to the differences in the knee ROMs during the two different landing activities. The TRAINED athletes are able to tolerate greater impact force in the regular landing and absorb greater impact force during the landing phase to facilitate energy generation during the takeoff phase in drop jump.