Effects Of Two Different Landing Protocols On Evaluating Impact Attenuation In Landing

Abstract

In impact attenuation studies for landing activities, two protocols are commonly employed to determine landing height: one based on absolute heights and the other based on percent of maximum jump height. However, no studies were conducted on the differences of these two protocols. PURPOSE To compare effects of two different landing protocols on evaluation of impact attenuation during a drop landing activity. METHODS Twelve male subjects (age: 23.5 ± 2.4 yrs) performed five drop landing trials from three heights in two different protocols. Subjects were divided into one of two groups based on their maximum vertical jump height (MVJ): elite (N=4) and non-elite (N=8). The MVJ was used as an index for lower extremity power capacity. All subjects performed five landing trials from heights of 40, 60, and 80 cm in the first protocol (PT1) and from 70%, 100%, and 130% of their MVJ height in the second protocol (PT2). Ground reaction force (GRF, 1080 Hz) and three-dimensional kinematic data (120 Hz, six cameras) were recorded simultaneously. Selected GRF variables were evaluated using a mixed design three-way repeated measures ANOVA (Group × Protocol × Height) with Group as the between-subject factor (p <0.05). RESULTS On average non-elite athletes landed from heights of 28, 40, and 52 cm while elite athletes landed from 39, 55, and 72 cm in PT2. Normalization of GRF variables by body weight (BW) revealed a significant increase in the peak GRF (F2, heel contact) with increased landing heights for both groups. A significant protocol × height interaction was also observed for non-elite athletes for F2. In PT1, the peak increased 54% (2.4 to 3.7 BW) and 43% (2.2 to 3.3 BW) from 40 to 80 cm for non-elite and elite groups, respectively. In PT2, F2 increased 42% (2.3 to 3.2 BW) and 31% (2.6 to 3.4 BW) from 70 to 130% MVJ for non-elite and elite groups, respectively. However, when F2 is normalized by potential energy instead non-elite and elite athletes demonstrated a 23% (6.0 to 4.7 N/J) and a 28% (5.6 to 4.0 N/J) decrease in F2 in PT1, respectively. The decreases were 24% (7.0 to 5.3 N/J) and 30% (5.5 to 3.9 N/J) for these two respective groups in PT2. CONCLUSION The results suggested an increased attenuation of the impact force during landing when the absolute height protocol is used compared to the protocol based on MVJ. The normalization of the impact force by BW seemed to be more appropriate in data analysis than the normalization by potential energy.