Using the Continuous Wavelet Transform to Characterize Differences Between Impact Signals from Non-Cleated and Cleated Turf Shoes

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URL: http://scholarworks.boisestate.edu/td/96/

Abstract

The continuous wavelet transform was used to characterize the time-frequency differences between impact forces from non-cleated and cleated turf shoes among male football athletes who perform cut and run activities. This research is significant because it elucidates how athletes experience different impact force and torque frequency content based on the type of shoe they are wearing.

The complex Morlet mother wavelet was used to analyze all ground reaction force and vertical ground reaction moment signals to create time-frequency power spectrum plots. For each signal, a statistical confidence interval was calculated and displayed along with the cone of influence caused by edge effects. These methods were used to ensure the results to be analyzed were genuine and not a result of edge effects due to the use of the wavelet transform technique or noise from the data acquisition system. To compare and contrast the power spectrum of both cleated and non-cleated turf shoes, a phase angle relationship was computed to find the correlation between the two signals, and then each wavelet transform was sliced at particular frequencies ranging from 11 Hz to 65 Hz to view this correlation at 5 Hz intervals. By calculating the percent difference between the maximum peaks along frequency slices ranging from 11 Hz to 65 Hz, it was possible to identify and characterize differences and similarities between force and moment signals.

In general, but not always, results show that the magnitudes of impact forces are directly related to the magnitudes of low frequency content between 11 Hz and 60 Hz, and the maximum values of the frequency percent differences vary within each GRF component and the vertical moment plots. For this study, non-cleated turf shoes increase the magnitude and duration of the response from the vertical ground reaction force and this is also particularly true for the medio-lateral ground reaction force and the ground reaction vertical moment of the same style of shoe.

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