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TECHNICAL PAPERS: Joint/Whole Body

Changes in Muscle Activity in Response to Different Impact Forces Affect Soft Tissue Compartment Mechanical Properties

[+] Author and Article Information
Katherine A. Boyer1

Division of Biomechanical Engineering, Department of Mechanical Engineering, 219 Durand Bldg., 496 Lomita Mall, Stanford University, Stanford, CA 94305-4038Kboyer@stanford.edu

Benno M. Nigg

Human Performance Lab, Faculty of Kinesiology, University of Calgary, Department of Mechanical Engineering, University of Calgary Canada

1

Corresponding author.

J Biomech Eng 129(4), 594-602 (Dec 13, 2006) (9 pages) doi:10.1115/1.2746384 History: Received June 07, 2006; Revised December 13, 2006

Electromyographic (EMG) activity is associated with several tasks prior to landing in walking and running including positioning the leg, developing joint stiffness and possibly control of soft tissue compartment vibrations. The concept of muscle tuning suggests one reason for changes in muscle activity pattern in response to small changes in impact conditions, if the frequency content of the impact is close to the natural frequency of the soft tissue compartments, is to minimize the magnitude of soft tissue compartment vibrations. The mechanical properties of the soft tissue compartments depend in part on muscle activations and thus it was hypothesized that changes in the muscle activation pattern associated with different impact conditions would result in a change in the acceleration transmissibility to the soft tissue compartments. A pendulum apparatus was used to systematically administer impacts to the heel of shod male participants. Wall reaction forces, EMG of selected leg muscles, soft tissue compartment and shoe heel cup accelerations were quantified for two different impact conditions. The transmissibility of the impact acceleration to the soft tissue compartments was determined for each subject/soft tissue compartment/shoe combination. For this controlled impact situation it was shown that changes in the damping properties of the soft tissue compartments were related to changes in the EMG intensity and/or mean frequency of related muscles in response to a change in the impact interface conditions. These results provide support for the muscle tuning idea—that one reason for the changes in muscle activity in response to small changes in the impact conditions may be to minimize vibrations of the soft tissue compartments that are initiated at heel-strike.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental setup as described in text above

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Figure 2

Mean soft tissue accelerations for one subject and one shoe condition for the quadriceps, hamstrings, triceps surae, and shoe

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Figure 3

Mean transmissibility values for the quadriceps, hamstrings, and triceps surae soft tissue compartments for the elastic shoe (dashed line) and the viscous shoe condition (solid line), n=11

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Figure 4

Individual transmissibility curves for the quadriceps for the elastic shoe (light) and the viscous shoe condition (dark). * indicates a positive muscle tuning relationship for the lower frequency range and # indicates a positive muscle tuning reaction for the upper frequency range with either the vastus medialis or rectus femoris EMG preactivation intensity results.

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Figure 5

Individual transmissibility curves for the hamstrings for the elastic shoe (light) and the viscous shoe condition (dark). * indicates a positive muscle tuning relationship for the lower frequency range and # indicates a positive muscle tuning reaction for the upper frequency range with biceps femoris EMG preactivation intensity results.

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Figure 6

Individual transmissibility curves for the triceps surae for the elastic shoe (light) and the viscous shoe condition (dark). * indicates a positive muscle tuning relationship for the lower frequency range and # indicates a positive muscle tuning reaction for the upper frequency range with biceps femoris EMG preactivation intensity results.

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