Masters Theses

Date of Award

3-2009

Degree Type

Thesis

Degree Name

Master of Science

Major

Exercise Science

Major Professor

Clare E Milner

Abstract

Background: Female athletes may be at increased risk of anterior cruciate ligament injury due to their mechanics when landing from a jump. In particular, high peak ground reaction force and frontal plane knee biomechanics may be altered. Hypothesis/Purpose: The purpose of this study was to determine if female recreational athletes can change their landing performance after a countermovement jump following a single session of verbal instruction. Study Design: Crossover Study Methods: Twelve female recreational athletes were recruited. Participants performed countermovement jumps under each of four conditions: control, knees over toes, equal weight distribution and soft landing. Three-dimensional lower extremity biomechanical data were collected. Results: Participants were able to land with lower peak vertical ground reaction force in the soft condition compared to the control (1.590 ± 0.2BW; 1.989 ± 0.7BW; p = 0.014).There was a corresponding increase in peak knee flexion angle in the soft condition compared to the control (94.6 ± 17.2°; 87.1 ± 19.9°; p = 0.023). The knees over toes instruction resulted in an increased maximum knee flexion angle compared to the control (101.4 ± 18.9°; 87.1 ± 19.9°; p = 0.003).This corresponded to an increase in eccentric work done in the knees over toes condition when compared to the control (-1.3 ± 0.5N/kg; -1.1 ± 0.4N/kg, p = 0.044). The equal weight distribution condition improved symmetry by almost half when compared to the control condition (21.089 ± 18.4; 10.562 ± 7.8; p = 0.024), indicating better distribution of load on both limbs following instruction. Conclusions: Participants were able to lower peak ground reaction force, increase maximum knee flexion angle, increase eccentric work done and reduce asymmetry according to specific verbal instructions during a single performance bout.However, there were no differences in total knee valgus motion and maximum knee valgus angle on instruction. Clinical Relevance: Simple verbal instructions regarding landing performance after a countermovement jump resulted in immediate improvements in biomechanical variables associated with increased risk of anterior cruciate ligament injury. If simple verbal instructions can be shown to also result in long term learning of these changes, they may be incorporated into injury prevention and rehabilitation programs to reduce the risk of further injury. Key Terms: Verbal instructions, ACL injury, symmetry landing, soft landing.

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