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TECHNICAL PAPERS: Bone/Orthopedics

Muscle Tuning During Running: Implications of an Un-tuned Landing

[+] Author and Article Information
Katherine A. Boyer, Benno M. Nigg

Human Performance Laboratory, Faculty of Kinesiology, Department of Mechanical Engineering, University of Calgary, 2500 University Dr. NW, Calgary, Alberta T2N 1N4, Canada

J Biomech Eng 128(6), 815-822 (Jun 13, 2006) (8 pages) doi:10.1115/1.2354202 History: Received October 14, 2005; Revised June 13, 2006

Background: The impact force in heel-toe running is an input signal into the body that initiates vibrations of the soft tissue compartments of the leg. These vibrations are heavily damped and the paradigm of muscle tuning suggests the body adapts to different input signals to minimize these vibrations. The objectives of the present study were to investigate the implications of not tuning a muscle properly for a landing with a frequency close to the resonance frequency of a soft tissue compartment and to look at the effect of an unexpected surface change on the subsequent step of running. Method: Thirteen male runners were recruited and performed heel-toe running over two surface conditions. The peak accelerations and biodynamic responses of the soft tissue compartments of the leg along with the EMG activity of related muscles were determined for expected soft, unexpected hard and expected hard landings. Results and Conclusions: For the unexpected hard landing there was a change in the input frequency of the impact force, shifting it closer to the resonance frequency of the soft tissue compartments. For the unexpected landing there was no muscle adaptation, as subjects did not know the running surface was going to change. In support of the muscle-tuning concept an increase in the soft tissue acceleration did occur. This increase was greater when the proximity of the input signal frequency was closer to the resonance frequency of the soft tissue compartment. Following the unexpected change in the input signal a change in pre-contact muscle activity to minimize soft tissue compartment vibrations was not found. This suggests if muscle tuning does occur it is not a continuous feedback response that occurs with every small change in the landing surface properties. In previous studies with significant adaptation periods to new input signals significant correlations between the changes in the input signal frequency and the EMG intensity have been shown, however, changes in soft tissue accelerations have not been found. The results of the present study showed that changes in these soft tissue accelerations can occur in response to a resonance frequency input signal when a muscle reaction has not happened.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 2

Transmissibility, H(f), (top) and phase, θ(f), (lower) for 12 subjects for the unexpected hard landing (dark dashed), the expected soft landing (light dashed) and the expected hard landing conditions (dark solid)

Grahic Jump Location
Figure 3

Transmission of the longitudinal shoe acceleration to the triceps surae acceleration for (a) Subject S and (b) Subject M. The frequency dependent response functions are averages of 10 and 13 trials. The dashed vertical lines indicated the frequency of the input signal for the expected soft and the unexpected hard landings.

Grahic Jump Location
Figure 1

Experimental set-up with a control condition (top) and a test condition (bottom). Light color indicates a soft surface, dark color indicates a hard surface. FP indicates the force plate locations along the track.

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