Residual Analysis

In biomechanical analysis is very common noise included in the signal, ie, signals that do not belong to the observed phenomenon or that are not of interest to the objective of the researcher. Thus, filtering procedures have been used to try to reduce the noise in the signal. Filtering is a mathematical procedure that tries to mitigate the noise and maintain signal belonging to the phenomenon analyzed. Different intensities filters are checked in an attempt to reduce the noise in the signal. Intense filters tend to reduce the noise in the signal, but at the same time can compromise data integrity. While less intense filters can ensure signal integrity, without properly remove noise. Thus, the residual analysis procedure was proposed by Winter (1990) to find an optimal theoretical intensity for attenuating noise in the signals.

To perform the residualanalysis, the  signal is filtered with various cutoff frequencies, near the cutoff frequency accredited as most appropriate. After the root mean square error (mean residual) of each filtered signal as a function of signal noise is calculated. The residue of each filtered signal, depending on their cutoff frequency used, is then analyzed graphically. According to Winter (1990) the projection of residue and filter cutoff frequencies provide a profile of curve with an abrupt increase in a given instant. This abrupt increase in the profile of the projection between residuals and cutting frequencies determines the great theoretical cutoff frequency of  filter .

Here's a link to download algorithm implemented in Matlab ® to perform residual analysis. Matlab Code

To use the function provided above you should:

- Select the frequency of your signal;

- Indicate the column for the variable to be tested in your data matrix;

- Select the filter order to be tested;

- Select the number of frequencies to be tested. Preferably enter a not too excessive number of frequencies in relation to the frequency cutoff commonly used for your type of signal. For example, for signals from the kinematic cutoff frequency most used is approximately 6 Hz, then we would use to test approximately 20 frequencies. As for signs that are commonly filtered at about 95 Hz would test with 200 frequencies. An excessive number of frequencies hinders visualization of the break point of the linearity of Residues x Cutting frequencies curve;

- Finally, point by clicking on the graph at the point of the break point of the linearity of Residues x Cutting frequencies curve.

References:

Winter D. Biomechanics and motor control of human movement. Wiley-Interscience: Toranto-Ontario, 1990.

Hope that is useful. 

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Biomechanical Analysis of Mae Geri

The technique of Karate Mae Geri consists of a front kick commonly used in competitions Shiai Kumite and Kata for beginners and advanced athletes, configuring itself as one of the techniques most often used in the sport.

Because it is a technique that has both a great damaging power and little exposure to his executor, this technique has been adopted by other modalities besides the karate. Another great advantage of Mae Geri is the difficulty with which the blow is perceived by the adversary. This is primarily to its short runtime, compared to other kicking techniques. It is no surprise Mae Geri be the protagonist of great knockouts in the main fights of today.

Its importance in performance in combat makes the Mae Geri object of study, and Biomechanics has effective tools to unravel its secrets.

Most commonly the Mae Geri runs from "Zenkutsu Dachi", advanced stance, kicking with the leg that is behind. The hip moves from approximately 30° of extension and flexes to approximately 90° of flexion simultaneously to the flexion and extension of knee. The angular behavior of the hip and knee added to the linear movement of the whole body towards the target make up the chain that generates kinetic energy necessary for performance linear of the foot toward the target.

When it comes to official competitions of Karate, by rule, contact with the target should be brief and may result in penalties if this requirement is not met. Competitive regulation in fact creates a new way for implementing Mae Geri regarding the implementation of the same in order to knockout. When the goal is to produce the strongest possible impact should reach peak linear acceleration of the segment (foot) preferably at the instant of contact with the target. However, the need to control the impact force means that there is deceleration prior to contact with the target.

Thus, the performance is optimized by reducing the time between the peak acceleration and the contact with the target. To do so, is to decrease the deceleration time, it requires an increase in the braking ability of the movement. This braking capability is performed by the antagonist muscles of the movement, in which case, the phase that precedes the contact, is the flexor muscles of the knee. Temporal characteristics, amplitude and amplitude over time (rate increase) of the activation of these muscles are responsible for the control of this ballistic movement. We see then that it is necessary and very important control of the mechanism of muscle co-contraction for speed control performance.

This is a preview of a research project being conducted at the Biomechanics Laboratory of UNESP - Rio Claro with high level athletes Karate. The research will mainly Biomechanical indicators that differentiate the high level Karate. These data are part of my PhD thesis, supervised by Prof. Dr. Mauro Gonçalves. The project also includes technical guidance and participation of Sensei Antonio Roberto Bendilatti. More information please contact us.

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