# Validation of Different Filters for Center of Pressure Measurements by a Cross-Section Study

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## Abstract

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## 1. Introduction

- The influence of the sampling duration effect,
- the influence of the sampling frequency, and
- the influence of digital filters.

## 2. Influence of Measurement Time and Frequency

## 3. Materials and Methods

#### 3.1. Method

- monopedal left, eyes open
- bipedal, eyes open
- monopedal right, eyes open
- bipedal, eyes closed

#### 3.2. Analysis

## 4. Results

#### 4.1. Influence of the Sampling Duration Effect

#### 4.2. Influence of Sampling Frequency

#### 4.3. Influence of Digital Filters

## 5. Discussion

- the influence of the sampling duration effect,
- the influence of the sampling frequency, and
- the influence of digital filters.

#### 5.1. Sampling Duration Effect

#### 5.2. Digital Filters

#### 5.3. Sampling Frequency

## 6. Summary

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 1.**Frequency spectrum of a CoP signal [7].

**Figure 2.**Representation of the temporal course of oscillations with different frequencies (0.1 Hz green; 0.01 Hz orange; 0.033 Hz black).

**Figure 4.**Absolute CoP length curve for bipedal stand over the measurement time, with open eyes (red) and closed eyes (black).

**Figure 5.**Absolute CoP length curve for monopedal stand over the measurement time, with left (red) and right leg (black).

**Figure 6.**Absolute CoP length curve as a function of the sampling frequency used in the bipedal state, with open (EO) and closed eyes (EC), respectively.

**Figure 7.**Absolute CoP length curve as a function of the sampling frequency used in the monopedal stand, for the left and right leg.

**Figure 8.**Result of the variation of different filter frequencies in the bipedal state for the measurement conditions of eyes open (red) and eyes closed (black).

**Figure 9.**Result of the variation of different filter frequencies for the measurement conditions of monopedal left (black) and monopedal right (red).

**Figure 10.**Representation of the mean frequency components in the entire spectrum per Hz in percent (blue) and the respective change in frequency per Hz (orange). The red line marks the limit at which the change was less than 0.1%/Hz.

**Figure 11.**Representation of the mean frequency components of the entire spectrum per Hz in percent (blue) after processing the CoP track with a Butterworth second order filter (black) and a Bessel seventh order filter (orange), where the respective cut-off frequency was 14 Hz.

Total Group | Male (52%) | Female (48%) | |
---|---|---|---|

Age (J.) | 39.9 ± 17.5 | 40.4 ± 16.6 | 40.54 ± 17.66 |

Weight (kg) | 75.8 ± 15.6 | 83.9 ± 13.7 | 66.13 ± 11.93 |

Size (cm) | 171.5 ± 25.8 | 180.9 ± 7.7 | 160.30 ± 34.21 |

BMI (kg/m^{2}) | 25.6 ± 3.8 | 24.2 ± 4.5 | |

Shoe size (EU) | 42.8 ± 2.7 | 42.5 ± 5.5 | 38.9 ± 1.5 |

Application | Filters | Parameter | Min. Sampling Frequencies | |
---|---|---|---|---|

Monopedal | Bipedal | |||

Fs < 13 | Chebyshev filter | 2^{nd} order | 600 Hz | 300 Hz |

13 ≤ fs < 16 | Butterworth filter | 3^{rd} order | 600 Hz | 300 Hz |

fs ≥ 16 Hz | Bessel filter | 7^{th} order | 600 Hz | 300 Hz |

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**MDPI and ACS Style**

Koltermann, J.J.; Gerber, M.; Beck, H.; Beck, M.
Validation of Different Filters for Center of Pressure Measurements by a Cross-Section Study. *Technologies* **2019**, *7*, 68.
https://doi.org/10.3390/technologies7040068

**AMA Style**

Koltermann JJ, Gerber M, Beck H, Beck M.
Validation of Different Filters for Center of Pressure Measurements by a Cross-Section Study. *Technologies*. 2019; 7(4):68.
https://doi.org/10.3390/technologies7040068

**Chicago/Turabian Style**

Koltermann, Jan Jens, Martin Gerber, Heidrun Beck, and Michael Beck.
2019. "Validation of Different Filters for Center of Pressure Measurements by a Cross-Section Study" *Technologies* 7, no. 4: 68.
https://doi.org/10.3390/technologies7040068