Doctoral Dissertations

Date of Award

8-2005

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Education

Major Professor

Songning Zhang

Committee Members

Edward T. Howley, Wendell P. Liemohn, Mehran Kasra

Abstract

The purposes ofthe dissertation were: 1) to examine the effects ofpower generation and two different landing protocols on the lower extremity during a landing activity, and 2) to examine the effects ofpower generation and gender on impact attenuation during a landing activity.

During the first study, eight elite male recreational athletes and eight non-elite male recreational athletes, selected based upon their maxinlunl jump heights, preformed drop landings in one of six conditions for two different protocols. Each subject landed from a height of40 cm, 60 cm and 80 cm in the first protocol (PT1) and from a height of 70%, 100%, and 1300/0 oftheir maximum vertical jump height in the second protocol (PT2). Ground reaction force (GRF) data were recorded using a force plate (OR6-7, AMTI) and kinematic data were recorded using a six camera motion analysis system (Vicon). Both the GRF and kinetic variables were normalized by potential energy. A Group x Protocol x Height mixed design repeated measures ANOV A with Group as the between subject factor was used to test the significance of selected variables. The nonelite athletes landed with a larger loading rate for the second GRF peak and a larger hip extension moment compared to the elite athletes. The non-elite athletes also landed with a greater ankle plantarflexion moment, knee adduction moment and ankle eccentric work in PT 1 whereas the elite athletes landed with a smaller ankle plantarflexion moment, knee adduction moment and ankle eccentric work. These findings suggest that the elite athletes ware better equipped to absorb the loads at impact and that the two groups of athletes responded differently.

During the second study, additional sixteen female subjects divided into the nonelite and elite groups prefornled drop landings in the same protocols as described in the first study. A Group x Gender xProtocol x Height mixed design repeated measures ANOV A with Group and Gender as the between subject factors was used to test the significance ofselected variables. No significant differences between the genders were observed. The elite group proved to land with smaller second GRF peak, greater ankle plantarflexion and knee extension moments compared to the non-elite group in PTI. These results demonstrated that the non-elite and elite athletes used different joint kinetic patterns to dissipate impact loading. Despite no statistical evidence supporting gender differences, females landed with a trend ofgreater percent increases in the first GRF peak while males landed with a trend ofsmaller second GRF peak. The elite males showed a decrease in the ankle eccentric work in PTlcompare to PT2. The females showed no change in the ankle eccentric work across the two protocols. These fmdings demonstrated that the males and females might have used different neuromuscular control ofthe lower extremity joints to attenuate the forces at impact.

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