# Augmenting Clinical Outcome Measures of Gait and Balance with a Single Inertial Sensor in Age-Ranged Healthy Adults

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## Abstract

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## 1. Introduction

## 2. Materials and Methods

#### 2.1. Participants

#### 2.2. Protocol and Data Collection

- The 10-m walk test (10MWT) of gait speed, with three trials each at a self-selected velocity (SSV) and fast velocity (FV). Increasing gait speed has been correlated with a higher quality of life [1] and community mobility [13]. The traditional clinical outcome of the 10MWT is average walking speed in the SSV and FV conditions. Participants walked over an instrumented walkway (GAITRite; CIR Systems, Inc., Franklin, NJ, USA) during this test, which was used as the gold standard for validating spatiotemporal gait characteristics computed from sensor data.
- Static postural stability condition of the Berg Balance Scale (BBS), including standing unsupported with feet apart (SU), standing with eyes closed (SEC), standing with feet together (SFT), (d) standing in tandem stance (ST) with their nondominant (or paretic) leg behind, and standing on one leg (SOL) on their nondominant (or paretic) leg. This test assesses functional balance and is associated with risk of falling [2]. A trained clinician scores each item on a 5-point ordinal scale, ranging from 0 (lowest function) to 4 (highest function). The traditional clinical outcome of the BBS is the total score.
- Timed Up and Go (TUG) test of functional mobility, with two trials collected. This test assesses functional mobility and is used to predict the risk of falls [14]. Participants began seated in a chair, rose to a standing position without use of their hands (Sit-to-Stand), walked 3 m (Walk), turned 180 degrees (Turn 1), walked 3 m back to the chair (Walk), turned 180° (Turn 2), and sat down in the chair without use of their hands (Stand-to-Sit). The traditional clinical outcome of the TUG is the total time required to complete the test.

#### 2.3. Sensor Technology

#### 2.4. Data Exclusions

#### 2.5. Data Analysis

#### 2.5.1. Clinical Meta-Feature Extraction

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#### 2.5.2. Features Summary

#### 2.6. Statistical Analysis

## 3. Results

#### 3.1. Validation of Spatiotemporal Gait Features

#### 3.2. Feature Independence between Clinical Tests

#### 3.3. Correlation between Age and Sensor-Derived Features

#### 3.4. Hierarchical Multivariate Regression for Age Effects in Sensor-Derived Features

#### 3.5. Differences between Age Groups and Stroke Rehabilitation Participant

## 4. Discussion

#### 4.1. BBS Static Balance Performance

#### 4.2. 10MWT Performance

#### 4.3. TUG Performance

#### 4.4. Strengths and Limitations

^{2}values, ranging from 0.104 to 0.604. This suggests that the 4-variable model does not explain most of the variance in this data and would be insufficient to predict outcomes accurately. However, the significance of age or other phenotype characteristics as predictors indicates a relationship between these variables and the sensor-based features. Further research is required to determine additional predictors of these sensor-based features, as well as their clinical relevance to age or impairment.

## 5. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## Appendix A

**Table A1.**Correlation of Berg Balance Scale (BBS) (Standing Unsupported) features with age (N = 49).

Feature ^{1} | Normality | Correlation with Age | Controlled for Weight and Height | ||
---|---|---|---|---|---|

p | r | p | r * | p * | |

F50% AP | 0.001 | −0.036 | 0.805 | −0.110 | 0.463 |

F50% ML | <0.001 | −0.146 | 0.316 | 0.001 | 0.994 |

F95% AP | 0.062 | −0.077 | 0.598 | −0.058 | 0.697 |

F95% ML | 0.009 | −0.426 ** | 0.002 | −0.384 ** | 0.008 |

SC AP | 0.266 | −0.134 | 0.359 | −0.120 | 0.421 |

SC ML | 0.188 | −0.266 | 0.064 | −0.253 | 0.086 |

Max Acc AP | <0.001 | −0.005 | 0.974 | 0.066 | 0.659 |

Max Acc ML | <0.001 | 0.063 | 0.667 | 0.177 | 0.235 |

Mean Acc AP | <0.001 | 0.123 | 0.399 | 0.088 | 0.558 |

Mean Acc ML | <0.001 | 0.179 | 0.218 | 0.135 | 0.365 |

RMS AP | <0.001 | 0.125 | 0.391 | 0.063 | 0.672 |

RMS ML | <0.001 | 0.184 | 0.205 | 0.166 | 0.265 |

Ellipse Angle AP | <0.001 | 0.103 | 0.483 | −0.187 | 0.209 |

Ellipse Angle ML | <0.001 | 0.198 | 0.173 | 0.248 | 0.092 |

95% Ellipse Area | <0.001 | 0.141 | 0.333 | 0.038 | 0.798 |

Ellipse Axis AP | <0.001 | 0.124 | 0.394 | 0.071 | 0.634 |

Ellipse Axis ML | <0.001 | 0.110 | 0.454 | 0.095 | 0.526 |

Jerk AP | <0.001 | −0.012 | 0.933 | −0.011 | 0.943 |

Jerk ML | <0.001 | −0.105 | 0.473 | −0.120 | 0.423 |

SwayV AP | <0.001 | 0.129 | 0.375 | 0.082 | 0.583 |

SwayV ML | <0.001 | 0.171 | 0.240 | 0.182 | 0.222 |

SPathA AP | <0.001 | −0.015 | 0.916 | −0.007 | 0.963 |

SPathA ML | <0.001 | −0.099 | 0.496 | −0.117 | 0.435 |

^{1}Features in italic were tested using the Spearman rank correlation; the remainder were tested with Pearson correlation. Bolded values indicate significant correlation: * p < 0.05, ** p < 0.01.

Feature ^{1} | Normality | Correlation with Age | Controlled for Weight and Height | ||
---|---|---|---|---|---|

p | r | p | r * | p * | |

F50% AP | 0.010 | 0.023 | 0.899 | −0.076 | 0.678 |

F50% ML | <0.001 | −0.233 | 0.185 | −0.308 | 0.087 |

F95% AP | <0.001 | −0.214 | 0.255 | −0.217 | 0.234 |

F95% ML | 0.008 | −0.145 | 0.412 | −0.168 | 0.358 |

SC AP | <0.001 | −0.115 | 0.516 | −0.147 | 0.422 |

SC ML | 0.305 | −0.378 ** | 0.007 | −0.369 * | 0.011 |

Max Acc AP | <0.001 | 0.196 | 0.266 | 0.151 | 0.410 |

Max Acc ML | <0.001 | 0.072 | 0.687 | 0.039 | 0.833 |

Mean Acc AP | <0.001 | 0.107 | 0.548 | 0.174 | 0.341 |

Mean Acc ML | <0.001 | 0.151 | 0.395 | 0.079 | 0.669 |

RMS AP | <0.001 | 0.109 | 0.540 | 0.159 | 0.385 |

RMS ML | <0.001 | 0.084 | 0.637 | 0.070 | 0.702 |

Ellipse Angle AP | <0.001 | −0.061 | 0.733 | 0.080 | 0.665 |

Ellipse Angle ML | <0.001 | −0.134 | 0.452 | −0.215 | 0.237 |

95% Ellipse Area | <0.001 | 0.049 | 0.782 | 0.092 | 0.617 |

Ellipse Axis AP | <0.001 | 0.110 | 0.536 | 0.143 | 0.435 |

Ellipse Axis ML | <0.001 | −0.004 | 0.981 | 0.042 | 0.819 |

Jerk AP | <0.001 | 0.068 | 0.703 | 0.042 | 0.818 |

Jerk ML | <0.001 | −0.125 | 0.481 | −0.089 | 0.628 |

SwayV AP | <0.001 | 0.182 | 0.303 | 0.175 | 0.338 |

SwayV ML | <0.001 | 0.180 | 0.308 | 0.105 | 0.569 |

SPathA AP | <0.001 | −0.006 | 0.973 | −0.031 | 0.868 |

SPathA ML | <0.001 | −0.209 | 0.236 | −0.128 | 0.486 |

^{1}Features in italic were tested using the Spearman rank correlation, while the remainder were tested with Pearson correlation. Bolded values indicate significant correlation: * p < 0.05, ** p < 0.01.

Feature ^{1} | Normality | Correlation with Age | Controlled for Weight and Height | ||
---|---|---|---|---|---|

p | r | p | r * | p * | |

F50% AP | <0.001 | −0.070 | 0.635 | −0.133 | 0.374 |

F50% ML | 0.101 | −0.101 | 0.489 | −0.097 | 0.517 |

F95% AP | 0.001 | −0.116 | 0.426 | −0.188 | 0.207 |

F95% ML | 0.162 | −0.312 * | 0.029 | −0.305 * | 0.037 |

SC AP | 0.040 | −0.067 | 0.647 | −0.153 | 0.304 |

SC ML | 0.121 | −0.269 | 0.062 | −0.261 | 0.076 |

Max Acc AP | <0.001 | 0.188 | 0.195 | 0.110 | 0.463 |

Max Acc ML | 0.004 | 0.134 | 0.360 | 0.106 | 0.477 |

Mean Acc AP | 0.003 | 0.101 | 0.492 | 0.163 | 0.273 |

Mean Acc ML | 0.001 | 0.154 | 0.292 | 0.187 | 0.209 |

RMS AP | 0.006 | 0.119 | 0.415 | 0.166 | 0.266 |

RMS ML | 0.009 | 0.145 | 0.319 | 0.186 | 0.211 |

Ellipse Angle AP | <0.001 | −0.023 | 0.876 | −0.193 | 0.195 |

Ellipse Angle ML | <0.001 | 0.140 | 0.339 | 0.099 | 0.508 |

95% Ellipse Area | <0.001 | 0.164 | 0.259 | 0.149 | 0.318 |

Ellipse Axis AP | 0.035 | 0.164 | 0.260 | 0.192 | 0.197 |

Ellipse Axis ML | <0.001 | 0.102 | 0.485 | 0.102 | 0.497 |

Jerk AP | 0.025 | −0.055 | 0.708 | −0.108 | 0.469 |

Jerk ML | 0.113 | −0.170 | 0.244 | −0.167 | 0.263 |

SwayV AP | <0.001 | 0.056 | 0.704 | 0.144 | 0.333 |

SwayV ML | <0.001 | 0.085 | 0.562 | 0.056 | 0.710 |

SPathA AP | 0.029 | −0.064 | 0.660 | −0.110 | 0.461 |

SPathA ML | 0.119 | −0.169 | 0.244 | −0.167 | 0.263 |

^{1}Features in italic were tested using the Spearman rank correlation; the remainder was tested with Pearson correlation. Bolded values indicate significant correlation: * p < 0.05, ** p < 0.01.

Feature ^{1} | Normality | Correlation with Age | Controlled for Weight and Height | ||
---|---|---|---|---|---|

p | r | p | r * | p * | |

F50% AP | <0.001 | −0.131 | 0.369 | −0.301 *
| 0.040 |

F50% ML | 0.033 | −0.045 | 0.760 | −0.076 | 0.610 |

F95% AP | <0.001 | −0.017 | 0.907 | 0.038 | 0.800 |

F95% ML | 0.055 | −0.050 | 0.733 | −0.055 | 0.712 |

SC AP | 0.032 | −0.087 | 0.550 | −0.152 | 0.308 |

SC ML | 0.133 | −0.076 | 0.605 | −0.077 | 0.608 |

Max Acc AP | <0.001 | 0.096 | 0.510 | −0.107 | 0.475 |

Max Acc ML | <0.001 | 0.031 | 0.834 | −0.132 | 0.378 |

Mean Acc AP | <0.001 | 0.238 | 0.099 | 0.089 | 0.550 |

Mean Acc ML | <0.001 | 0.222 | 0.125 | 0.157 | 0.291 |

RMS AP | <0.001 | 0.163 | 0.264 | 0.024 | 0.870 |

RMS ML | <0.001 | 0.166 | 0.254 | 0.041 | 0.785 |

Ellipse Angle AP | <0.001 | −0.070 | 0.634 | −0.064 | 0.668 |

Ellipse Angle ML | 0.040 | 0.070 | 0.631 | 0.049 | 0.746 |

95% Ellipse Area | <0.001 | 0.179 | 0.219 | −0.042 | 0.779 |

Ellipse Axis AP | <0.001 | 0.113 | 0.441 | −0.021 | 0.890 |

Ellipse Axis ML | <0.001 | 0.231 | 0.110 | 0.068 | 0.651 |

Jerk AP | 0.137 | 0.172 | 0.238 | 0.189 | 0.203 |

Jerk ML | 0.176 | 0.114 | 0.434 | 0.126 | 0.399 |

SwayV AP | <0.001 | 0.105 | 0.475 | −0.016 | 0.917 |

SwayV ML | <0.001 | −0.032 | 0.825 | −0.071 | 0.635 |

SPathA AP | 0.197 | 0.160 | 0.273 | 0.177 | 0.233 |

SPathA ML | 0.323 | 0.106 | 0.471 | 0.118 | 0.430 |

^{1}Features in italic were tested using the Spearman rank correlation; the remainder was tested with Pearson correlation. Bolded values indicate significant correlation: * p < 0.05, ** p < 0.01.

Feature ^{1} | Normality | Correlation with Age | Controlled for Weight and Height | ||
---|---|---|---|---|---|

p | r | p | r * | p * | |

F50% AP | <0.001 | −0.015 | 0.98 | 0.084 | 0.577 |

F50% ML | 0.106 | −0.169 | 0.274 | −0.155 | 0.299 |

F95% AP | 0.100 | 0.014 | 0.922 | 0.029 | 0.848 |

F95% ML | <0.001 | −0.103 | 0.479 | −0.143 | 0.337 |

SC AP | 0.042 | 0.037 | 0.800 | 0.052 | 0.726 |

SC ML | 0.500 | −0.175 | 0.228 | −0.171 | 0.250 |

Max Acc AP | <0.001 | 0.185 | 0.202 | 0.139 | 0.353 |

Max Acc ML | <0.001 | 0.432 ** | 0.002 | 0.348 * | 0.017 |

Mean Acc AP | <0.001 | 0.226 | 0.118 | 0.173 | 0.245 |

Mean Acc ML | <0.001 | 0.361 * | 0.011 | 0.377 ** | 0.009 |

RMS AP | <0.001 | 0.226 | 0.118 | 0.166 | 0.264 |

RMS ML | <0.001 | 0.356 * | 0.012 | 0.379 ** | 0.009 |

Ellipse Angle AP | <0.001 | 0.184 | 0.206 | 0.177 | 0.235 |

Ellipse Angle ML | 0.018 | −0.049 | 0.753 | −0.029 | 0.848 |

95% Ellipse Area | <0.001 | 0.292 * | 0.042 | 0.191 | 0.199 |

Ellipse Axis AP | <0.001 | 0.354 * | 0.013 | 0.316 * | 0.031 |

Ellipse Axis ML | <0.001 | 0.190 | 0.192 | 0.140 | 0.347 |

Jerk AP | <0.001 | 0.234 | 0.105 | 0.152 | 0.306 |

Jerk ML | <0.001 | 0.273 | 0.058 | 0.241 | 0.103 |

SwayV AP | <0.001 | 0.182 | 0.210 | 0.205 | 0.167 |

SwayV ML | <0.001 | 0.283 * | 0.049 | 0.324 * | 0.026 |

SPathA AP | <0.001 | 0.257 | 0.074 | 0.178 | 0.232 |

SPathA ML | <0.001 | 0.268 | 0.063 | 0.239 | 0.106 |

^{1}Features in italic were tested using the Spearman rank correlation; the remainder was tested with Pearson correlation. Bolded values indicate significant correlation: * p < 0.05, ** p < 0.01.

Feature ^{1} | Normality | Correlation with Age | Controlled for Weight and Height | ||
---|---|---|---|---|---|

p | r | p | r * | p * | |

Mean Vertical Displacement | <0.001 | −0.201 | 0.167 | −0.177 | 0.234 |

Mean Stance Time | 0.163 | 0.219 | 0.133 | 0.313 * | 0.032 |

Mean Step Time | 0.075 | 0.183 | 0.209 | 0.267 | 0.069 |

Mean Stride Time | 0.073 | 0.179 | 0.219 | 0.541 | 0.264 |

Mean Swing Time | 0.040 | 0.082 | 0.575 | 0.183 | 0.219 |

Mean Step Length | 0.079 | −0.341 * | 0.017 | −0.367 * | 0.011 |

Maximum Power Frequency | <0.001 | −0.221 | 0.127 | −0.216 | 0.144 |

Stance Time Symmetry Ratio | 0.826 | −0.057 | 0.697 | −0.049 | 0.742 |

Step Length Symmetry Ratio | <0.001 | −0.152 | 0.296 | −0.167 | 0.263 |

Duration | <0.001 | 0.235 | 0.104 | 0.309 * | 0.034 |

Mean Velocity | 0.116 | −0.658 ** | 0.008 | −0.387 ** | 0.007 |

N Steps | 0.126 | 0.280 | 0.051 | 0.260 | 0.077 |

Velocity Difference, FV – SSV | <0.001 | −0.013 | 0.931 | −0.004 | 0.979 |

^{1}Features in italics were tested using the Spearman rank correlation; the remainder was tested with Pearson correlation. Bolded values indicate significant correlation: * p < 0.05, ** p < 0.01.

Feature ^{1} | Normality | Correlation with Age | Controlled for Weight and Height | ||
---|---|---|---|---|---|

p | r | p | r * | p * | |

Mean Vertical Displacement | 0.383 | −0.251 | 0.086 | −0.272 | 0.067 |

Mean Stance Time | 0.502 | 0.020 | 0.895 | 0.059 | 0.699 |

Mean Step Time | 0.240 | 0.014 | 0.924 | 0.049 | 0.747 |

Mean Stride Time | 0.248 | 0.012 | 0.936 | 0.048 | 0.753 |

Mean Swing Time | 0.056 | 0.010 | 0.948 | 0.038 | 0.800 |

Mean Step Length | 0.105 | −0.315 * | 0.029 | −0.370 * | 0.011 |

Maximum Power Frequency | 0.003 | −0.355 * | 0.013 | −0.363 * | 0.013 |

Stance Time Symmetry Ratio | 0.461 | −0.078 | 0.598 | −0.072 | 0.632 |

Step Length Symmetry Ratio | 0.288 | 0.044 | 0.768 | 0.040 | 0.790 |

Duration | 0.043 | 0.271 | 0.062 | 0.327 * | 0.026 |

Mean Velocity | 0.383 | −0.364 * | 0.011 | 0.370 * | 0.011 |

N Steps | 0.502 | 0.365 * | 0.011 | 0.367 * | 0.012 |

^{1}Features in italics were tested using the Spearman rank correlation; the remainder was tested with Pearson correlation. Bolded values indicate significant correlation: * p < 0.05, ** p < 0.01.

Feature ^{1} | Normality | Correlation with Age | Controlled for Weight and Height | ||
---|---|---|---|---|---|

p | r | p | r * | p * | |

SIT-TO-STAND | |||||

Range Pitch Vel (i–ii) | 0.408 | −0.307 * | 0.037 | −0.290 | 0.051 |

Range Pitch Vel (ii–iii) | 0.554 | −0.212 | 0.148 | −0.195 | 0.194 |

SD Pitch Vel (i–iii) | 0.271 | −0.295 * | 0.042 | −0.279 | 0.060 |

Mean Pitch Vel (i–iii) | 0.045 | 0.290 * | 0.046 | 0.309 * | 0.036 |

Median Pitch Vel (i–iii) | 0.222 | 0.132 | 0.372 | 0.110 | 0.466 |

Max Pitch Vel (i–ii) | 0.825 | 0.314 * | 0.030 | 0.301 * | 0.042 |

Max Pitch Vel (ii–iii) | 0.152 | 0.093 | 0.528 | 0.104 | 0.493 |

Mean Pitch Acc (i–ii) | <0.001 | 0.269 | 0.065 | 0.391 ** | 0.007 |

Mean Pitch Acc (ii–iii) | 0.259 | −0.291 * | 0.045 | −0.289 | 0.052 |

Mean Acc AP (i–iii) | 0.182 | −0.207 | 0.158 | −0.203 | 0.176 |

SD Acc AP (i–iii) | 0.192 | −0.020 | 0.890 | 0.021 | 0.892 |

Median Acc AP (i–iii) | 0.454 | −0.085 | 0.563 | −0.120 | 0.426 |

Duration (i–iii) | 0.511 | 0.352 * | 0.014 | 0.344 * | 0.019 |

WALK | |||||

RMS Acc AP | 0.097 | 0.378 ** | 0.008 | 0.366 * | 0.012 |

RMS Acc ML | 0.145 | 0.110 | 0.455 | 0.103 | 0.495 |

RMS Acc V | 0.047 | 0.276 * | 0.058 | 0.299 * | 0.043 |

Mean Step Time | 0.491 | 0.022 | 0.884 | 0.034 | 0.822 |

SD Step Time | 0.025 | −0.120 | 0.418 | −0.110 | 0.466 |

N Steps | 0.003 | 0.403 ** | 0.005 | 0.483 ** | 0.001 |

Duration | <0.001 | 0.432 ** | 0.002 | 0.488 ** | 0.001 |

TURN 1 | |||||

Max Yaw Vel | 0.397 | −0.225 | 0.125 | −0.213 | 0.154 |

Mean Yaw Acc (i–ii) | <0.001 | −0.203 | 0.167 | −0.181 | 0.228 |

Mean Yaw Acc (ii–iii) | <0.001 | 0.185 | 0.209 | 0.203 | 0.177 |

N Steps | 0.460 | −0.169 | 0.251 | −0.187 | 0.212 |

Duration | 0.217 | 0.100 | 0.500 | 0.094 | 0.535 |

TURN 2 | |||||

Max Yaw Vel | 0.829 | −0.457 ** | 0.001 | −0.455 ** | 0.001 |

Mean Yaw Acc (i–ii) | <0.001 | −0.569 ** | <0.001 | −0.581 ** | <0.001 |

Mean Yaw Acc (ii–iii) | 0.014 | 0.366 * | 0.010 | 0.315 * | 0.033 |

N Steps | 0.947 | 0.297 * | 0.040 | 0.296 * | 0.046 |

Duration | 0.246 | 0.365 * | 0.011 | 0.391 ** | 0.007 |

STAND-TO-SIT | |||||

Range Pitch Vel (i–ii) | 0.026 | −0.259 | 0.076 | −0.357 * | 0.015 |

Range Pitch Vel (ii–iii) | 0.699 | −0.290 * | 0.045 | −0.303 * | 0.041 |

SD Pitch Vel (i–iii) | 0.101 | −0.313 * | 0.030 | −0.335 * | 0.023 |

Mean Pitch Vel (i–iii) | 0.362 | −0.066 | 0.654 | −0.084 | 0.581 |

Median Pitch Vel (i–iii) | 0.761 | −0.066 | 0.657 | −0.097 | 0.521 |

Max Pitch Vel (i–ii) | 0.002 | 0.213 | 0.146 | 0.315 * | 0.033 |

Max Pitch Vel (ii–iii) | 0.995 | −0.223 | 0.127 | −0.234 | 0.117 |

Mean Acc Pitch (i–ii) | 0.001 | 0.328 * | 0.023 | 0.291 * | 0.050 |

Mean Acc Pitch (ii–iii) | 0.002 | −0.362 * | 0.012 | −0.422 ** | 0.004 |

Mean Acc AP (i–iii) | 0.839 | −0.365 * | 0.011 | −0.398 ** | 0.006 |

SD Acc AP (i–iii) | 0.005 | −0.315 * | 0.029 | −0.326 * | 0.027 |

Median Acc AP (i–iii) | 0.520 | −0.259 | 0.076 | −0.279 | 0.060 |

Duration (i–iii) | <0.001 | 0.226 | 0.122 | 0.238 | 0.112 |

^{1}Features in italics were tested using the Spearman rank correlation; the remainder was tested with Pearson correlation. Bolded values indicate significant correlation: * p < 0.05, ** p < 0.01.

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**Figure 1.**The BioStampRC sensor was secured to the skin at the L5 vertebra with adhesive film, aligned with the local coordinate system of the vertebra. The sensor recorded triaxial accelerometer and gyroscope signals. Positive and negative axes of the sensor were pre-defined by the BioStampRC and later aligned with the true (global) coordinate system for anteroposterior (AP), mediolateral (ML), and vertical (V) directions.

**Figure 2.**Flowchart to estimate spatiotemporal gait features, combining methodologies from (

**a**) [15,16], (

**b**) [16,23], (

**c**) [17], (

**d**) [18], (

**e**) [16], and (

**f**) [16,20]. ${a}_{\mathrm{V}}$, ${a}_{\mathrm{ML}}$, ${a}_{\mathrm{AP}}$ = acceleration in vertical, mediolateral, and anterposterior directions, respectively. CWT = continuous wavelet transform; ${t}_{\mathrm{IC}}$ = times of initial contact; ${t}_{\mathrm{EC}}$ = times of end contact; i = index of gait cycle; ${T}_{\mathrm{Stance}}$ = stance time; ${T}_{\mathrm{Stride}}$ = stride time; ${T}_{\mathrm{Step}}$ = step time; ${T}_{\mathrm{Swing}}$ = swing time; EMD = empirical mode decomposition; h = vertical displacement of CoM; L = distance from sensor (approximately located at CoM) to ground during upright standing; $K$ = optimization constant; ${L}_{\mathrm{Step}}$ = step length; ${V}_{\mathrm{Step}}$ = step velocity.

**Figure 3.**Flowchart for Timed Up and Go (TUG) phase detection (sit/stand transitions and turning). DWT = discrete wavelet transform; db5 = Daubechies 5; LA = level of approximation.

**Figure 4.**Examples of features estimated from the different clinical tests. (

**a**) Temporal gait estimation by the CWT method. (

**b**) Step length estimation by the inverted pendulum model. (

**c**) 95% Ellipse area, axis, and angles. (

**d**) Frequency domain measures from the Berg Balance Scale (BBS) (F50%, F95%, and SC). (

**e**) Phase estimation in the Timed Up and Go (TUG) by the DWT method.

**Figure 5.**Bland–Altman and linear correlation plots between the BioStampRC and gold standard measures for spatiotemporal features of gait. (

**a**) Stance time, (

**b**) swing time, (

**c**) step time, (

**d**) step length, (

**e**) gait velocity, and (

**f**) step count. RMSE = Root-Mean-Squared Error; ICC = Intraclass Correlation; LoA = Limits of Agreement; p-value = D’Agostino–Pearson normality test.

**Figure 6.**Correlation coefficients between sensor-derived features across clinical tests. BBS Standing Unsupported: 1–2. F50% (ML/AP), 3–4. F95% (ML/AP), 5–6. SC (AP/ML), 7–8. Max Acc (AP/ML), 9–10. Mean Acc (AP/ML), 11–12. RMS (AP/ML), 13–14. Ellipse Angle (AP/ML). 15. Ellipse Area, 16–17. Ellipse Axis (AP/ML), 18–19. Jerk (AP/ML), 20–21. SwayV (AP/ML), 22–23. SPathA (AP/ML). 10MWT SSV: 24. Mean Vertical Displacement, 25. Stance Time, 26. Step Time, 27. Stride Time, 28. Swing Time, 29. Step Length, 30. Power Frequency, 31. Stance Time Ratio, 32. Step Length Ratio, 33. Duration, 34. Mean Velocity, 35. N Steps. TUG Sit-to-Stand: 36–37. Range Pitch Vel (i–ii/ii–iii), 38. SD Pitch Vel (i–iii), 39. Mean Pitch Vel (i–iii), 40. Median Pitch Vel (i–iii), 41–42. Max Pitch Vel (i–ii/ii–iii), 43–44. Mean Pitch Acc (i–ii/ii–iii), 45. Mean Acc (AP), 46. SD Acc (AP), 47. Duration. 48. Median Acc (AP). TUG Stand-to-Sit: 49–50. Range Pitch Vel (i–ii/ii–iii), 51. SD Pitch Vel (i–iii), 52. Mean Pitch Vel (i–iii), 53. Median Pitch Vel (i–iii), 54–55. Max Pitch Vel (i–ii/ii–iii), 56–57. Mean Pitch Acc (i–ii/ii–iii), 58. Mean Acc (AP), 59. SD Acc (AP), 60. Duration, 61. Median Acc (AP). TUG Turn 1: 62. Duration, 63. N Steps, 64. Max Yaw Vel, 65–66. Mean Yaw Acc (i–ii/ii–iii). TUG Walk: 67–69. RMS (AP/ML/V), 70. N Steps, 71. Mean Step Time, 72. SD Step Time, 73. Velocity Difference (FV−SSV).

**Figure 7.**Clinical outcome comparison between (

**a**) traditional measures and (

**b**) sample features estimated by the sensor-derived approach in three age groups, as well as in a single stroke patient (42 days post-stroke, blue bar). SSV = Self-Selected Velocity; FV = Fast Velocity; SU = Standing Unsupported; SEC = Standing Eyes Closed; SFT = Standing Feet Together; ST = Standing Tandem stance; SOL = Standing on One Leg.

Group | N | Age (years) | Height (cm) | Weight (kg) | Female | Male |
---|---|---|---|---|---|---|

Ages 20–34 | 14 | 26.4 (3.9) | 173.0 (11.4) | 71.5 (13.8) | 6 | 8 |

Ages 35–54 | 19 | 43.7 (5.8) | 169.9 (12.8) | 79.2 (23.7) | 11 | 8 |

Ages 55–70 | 16 | 61.8 (5.1) | 169.7 (7.5) | 73.1 (15.9) | 8 | 8 |

Stroke | 1 | 57 | 185.4 | 82.8 | 0 | 1 |

Test | Feature | Reference | Units | Definition |
---|---|---|---|---|

BBS | F50% (AP, ML) | [28,29] | Hz | Frequency accounting for 50% of total power of the signal |

F95% (AP, ML) | [28,29] | Hz | Frequency accounting for 95% of total power of the signal | |

SC (AP, ML) | [28,29] | Hz | Spectral centroid (indicates center of mass of the spectrum) | |

Max Acc (AP, ML) | m/s^{2} | Maximum acceleration | ||

Mean Acc (AP, ML) | m/s^{2} | Mean acceleration | ||

RMS (AP, ML) | [12,28] | m/s^{2} | Root mean square of acceleration | |

Ellipse Angles (AP, ML) | [12,29] | m/s^{2} | Angles of 95% of ellipse orientation | |

95% Ellipse Area | m^{2}/s^{4} | Area of 95% ellipse | ||

Ellipse Axis (AP, ML) | [29] | m/s^{2} | Length of 95% ellipse axis | |

Jerk (AP, ML) | [12] | m/s^{3} | Smoothness of sway (time derivative of acceleration) | |

SwayV (AP, ML) | [12,28] | m/s | Mean sway velocity | |

SPathA (AP, ML) | [28] | m/s^{2} | Total acceleration path | |

10MWT | Mean Vertical Displacement | m | Vertical displacement of the body Center of Mass (CoM) | |

Mean Stance Time (SSV, FV) | [16] | s | Length of time for which the foot is in contact with the ground | |

Mean Step Time (SSV, FV) | [16] | s | Length of time between successive ICs of opposite feet | |

Mean Stride Time (SSV, FV) | [16] | s | Length of time between successive ICs of the same foot | |

Mean Swing Time (SSV, FV) | [16] | s | Length of time for which the foot is not in contact with the ground | |

Mean Step Length (SSV, FV) | [16] | cm | Distance between successive ICs of opposite feet | |

Maximum Power Frequency (SSV, FV) | (m/s^{2})^{2}/Hz | Maximum power from the power spectral density of vertical acceleration | ||

Stance Time Symmetry Ratio (SSV, FV) | unitless | Stance time ratio of right and left leg (temporal symmetry) | ||

Step Length Symmetry Ratio (SSV, FV) | unitless | Step length ratio of right and left leg (spatial symmetry) | ||

Duration (SSV, FV) | s | Time required to complete the test, averaged over three trials | ||

Mean Velocity (SSV, FV) | [16] | m/s | Mean step velocity | |

N Steps (SSV, FV) | unitless | Number of steps taken | ||

Velocity Difference, FV–SSV | m/s | Difference in average walking velocity between SSV and FV modes | ||

TUG—Sit to Stand, Stand to Sit | Range Pitch Vel (i–ii, ii–iii)^{2} | [25] | °/s | Difference between the minimum and maximum values of angular velocity (pitch axis) |

SD Pitch Vel (i–iii) | [25] | °/s | Standard deviation of angular velocity (pitch axis) | |

Mean Pitch Vel (i–iii) | [25] | °/s | Mean value of angular velocity (pitch axis) | |

Median Pitch Vel (i–iii) | [25] | °/s | Median value of angular velocity (pitch axis) | |

Max Pitch Vel (i–ii, ii–iii) | [25] | °/s | Maximum value of angular velocity (pitch axis) | |

Mean Pitch Acc (i–ii, ii–iii) | [25] | °/s^{2} | Average rate of change of angular velocity (angular acceleration, pitch axis) | |

Mean Acc AP (i–iii) | [25] | m/s^{2} | Mean phase value of AP acceleration | |

SD Acc AP (i–iii) | [25] | m/s^{2} | Standard deviation of AP acceleration | |

Median Acc AP (i–iii) | [25] | m/s^{2} | Median value of AP acceleration | |

Duration (i–iii) | [25] | s | Time required to complete the phase | |

TUG—Turn 1, Turn 2 | N Steps | [25] | unitless | Number of steps taken |

Max Yaw Vel | [25] | °/s | Maximum value of angular velocity magnitude (yaw axis) | |

Mean Yaw Acc (i–ii, ii–iii) | [25] | °/s^{2} | Average rate of change of angular velocity (angular acceleration, yaw axis) | |

Duration | [25] | s | Time required to complete the turn phase | |

TUG—Walk 1 + Walk 2 | RMS Acc (AP, ML, V) | [25] | m/s^{2} | Root mean square of acceleration |

Mean Step Time | [25] | s | Mean step time over the two walking phases | |

SD Step Time | [25] | s | Standard deviation of step time | |

N Steps | [25] | unitless | Number of steps taken | |

Duration | [25] | s | Time required to complete the walking phase | |

Naturalistic Walking | N Steps | unitless | Number of steps taken |

**Table 3.**Hierarchical multiple regression analysis from the features that showed non-negligible correlations with age (|r| ≥ 0.3, p < 0.05) after correcting for weight and height.

Feature | Model no. | Standardized Beta Coefficients | R^{2} | R^{2} Change | F Change | df | p | |||
---|---|---|---|---|---|---|---|---|---|---|

Weight | Height | Sex | Age | |||||||

BBS-SU | ||||||||||

F95% ML | 1 | −0.246 | 0.061 | 0.061 | 3.03 | 1, 47 | 0.088 | |||

2 | −0.429 | 0.295 | 0.114 | 0.054 | 2.78 | 1, 46 | 0.10 | |||

3 | −0.416 | 0.347 | −0.076 | 0.116 | 0.002 | 0.10 | 1, 45 | 0.75 | ||

4 | −0.374 | 0.305 | −0.074 | −0.363 | 0.247 | 0.131 | 7.62 | 1, 44 | 0.008 | |

BBS-SEC | ||||||||||

SC ML | 1 | −0.100 | 0.010 | 0.010 | 0.48 | 1, 47 | 0.49 | |||

2 | −0.206 | 0.170 | 0.028 | 0.018 | 0.84 | 1, 46 | 0.37 | |||

3 | −0.184 | 0.251 | −0.119 | 0.033 | 0.005 | 0.23 | 1, 45 | 0.63 | ||

4 | −0.143 | 0.209 | −0.117 | −0.365 | 0.165 | 0.132 | 6.95 | 1, 44 | 0.012 | |

BBS-SFT | ||||||||||

F95% ML | 1 | −0.165 | 0.027 | 0.027 | 1.31 | 1, 47 | 0.26 | |||

2 | −0.212 | 0.077 | 0.031 | 0.004 | 0.17 | 1, 46 | 0.68 | |||

3 | −0.162 | 0.268 | −0.281 | 0.058 | 0.028 | 1.31 | 1, 45 | 0.26 | ||

4 | −0.127 | 0.234 | −0.279 | −0.301 | 0.148 | 0.090 | 4.65 | 1, 44 | 0.037 | |

BBS-ST | ||||||||||

F50% AP | 1 | 0.022 | <0.001 | <0.001 | 0.02 | 1, 47 | 0.88 | |||

2 | −0.073 | 0.152 | 0.015 | 0.015 | 0.68 | 1, 46 | 0.42 | |||

3 | -0.071 | 0.158 | −0.008 | 0.015 | <0.001 | 0.001 | 1, 45 | 0.98 | ||

4 | −0.037 | 0.123 | −0.006 | −0.300 | 0.104 | 0.089 | 4.39 | 1, 44 | 0.042 | |

BBS-SOL | ||||||||||

Max Acc ML | 1 | −0.059 | 0.003 | 0.003 | 0.16 | 1, 47 | 0.69 | |||

2 | −0.157 | 0.158 | 0.019 | 0.015 | 0.72 | 1, 46 | 0.40 | |||

3 | −0.092 | 0.405 | −0.362 | 0.065 | 0.046 | 2.20 | 1, 45 | 0.15 | ||

4 | −0.131 | 0.445 | −0.364 | 0.347 | 0.184 | 0.119 | 6.42 | 1, 44 | 0.015 | |

Mean Acc ML | 1 | −0.120 | 0.014 | 0.014 | 0.69 | 1, 47 | 0.41 | |||

2 | −0.164 | 0.070 | 0.017 | 0.003 | 0.14 | 1, 46 | 0.71 | |||

3 | −0.098 | 0.321 | −0.368 | 0.065 | 0.047 | 2.27 | 1, 45 | 0.14 | ||

4 | −0.140 | 0.363 | −0.370 | 0.376 | 0.205 | 0.140 | 7.74 | 1, 44 | 0.008 | |

RMS ML | 1 | −0.091 | 0.008 | 0.008 | 0.40 | 1, 47 | 0.53 | |||

2 | −0.159 | 0.109 | 0.016 | 0.007 | 0.34 | 1, 46 | 0.56 | |||

3 | −0.098 | 0.342 | −0.341 | 0.056 | 0.041 | 1.94 | 1, 45 | 0.17 | ||

4 | −0.140 | 0.385 | −0.343 | 0.378 | 0.198 | 0.142 | 7.78 | 1, 44 | 0.008 | |

Ellipse Axis AP | 1 | −0.030 | 0.001 | 0.001 | 0.04 | 1, 47 | 0.84 | |||

2 | −0.110 | 0.128 | 0.011 | 0.010 | 0.47 | 1, 46 | 0.50 | |||

3 | −0.042 | 0.386 | −0.377 | 0.061 | 0.050 | 2.38 | 1, 45 | 0.13 | ||

4 | −0.078 | 0.422 | −0.379 | 0.316 | 0.160 | 0.099 | 5.19 | 1, 44 | 0.028 | |

SwayV ML | 1 | −0.187 | 0.035 | 0.035 | 1.70 | 1, 47 | 0.20 | |||

2 | −0.192 | 0.009 | 0.035 | <0.001 | 0.002 | 1, 46 | 0.96 | |||

3 | −0.109 | 0.322 | −0.460 | 0.109 | 0.074 | 3.725 | 1, 45 | 0.060 | ||

4 | −0.146 | 0.359 | −0.462 | 0.321 | 0.211 | 0.102 | 5.678 | 1, 44 | 0.022 | |

10MWT-SSV | ||||||||||

Mean Stance Time | 1 | 0.373 | 0.139 | 0.139 | 7.59 | 1, 47 | 0.008 | |||

2 | 0.051 | 0.521 | 0.307 | 0.168 | 11.14 | 1, 46 | 0.002 | |||

3 | 0.016 | 0.384 | 0.200 | 0.321 | 0.014 | 0.91 | 1, 45 | 0.35 | ||

4 | −0.022 | 0.423 | 0.206 | 0.265 | 0.390 | 0.069 | 4.97 | 1, 44 | 0.031 | |

Mean Step Length | 1 | 0.388 | 0.151 | 0.151 | 8.34 | 1, 47 | 0.006 | |||

2 | 0.076 | 0.506 | 0.309 | 0.158 | 10.53 | 1, 46 | 0.002 | |||

3 | 0.026 | 0.313 | 0.280 | 0.336 | 0.027 | 1.84 | 1, 45 | 0.18 | ||

4 | 0.069 | 0.268 | 0.272 | −0.305 | 0.427 | 0.092 | 7.03 | 1, 44 | 0.011 | |

Duration | 1 | 0.186 | 0.035 | 0.035 | 1.69 | 1, 47 | 0.20 | |||

2 | 0.100 | 0.139 | 0.047 | 0.012 | 0.58 | 1, 46 | 0.45 | |||

3 | 0.087 | 0.089 | 0.074 | 0.049 | 0.002 | 0.09 | 1, 45 | 0.77 | ||

4 | 0.044 | 0.134 | 0.082 | 0.306 | 0.140 | 0.092 | 4.69 | 1, 44 | 0.036 | |

Mean Velocity | 1 | −0.044 | 0.002 | 0.002 | 0.09 | 1, 47 | 0.77 | |||

2 | −0.009 | −0.057 | 0.004 | 0.002 | 0.09 | 1, 46 | 0.76 | |||

3 | −0.010 | −0.063 | 0.009 | 0.004 | <0.001 | 0.001 | 1, 45 | 0.97 | ||

4 | 0.044 | −0.121 | −0.001 | −0.388 | 0.152 | 0.148 | 7.68 | 1, 44 | 0.008 | |

10MWT-FV | ||||||||||

Mean Step Length | 1 | 0.516 | 0.266 | 0.266 | 16.67 | 1, 47 | <0.001 | |||

2 | 0.221 | 0.485 | 0.414 | 0.148 | 11.38 | 1, 46 | 0.002 | |||

3 | 0.122 | 0.097 | 0.566 | 0.527 | 0.113 | 10.50 | 1, 45 | 0.002 | ||

4 | 0.160 | 0.055 | 0.559 | −0.281 | 0.604 | 0.077 | 8.41 | 1, 44 | 0.006 | |

Maximum Power Frequency | 1 | 0.138 | 0.019 | 0.019 | 0.89 | 1, 47 | 0.35 | |||

2 | 0.140 | −0.004 | 0.019 | <0.001 | 0.001 | 1, 46 | 0.98 | |||

3 | 0.095 | −0.179 | 0.255 | 0.042 | 0.023 | 1.05 | 1, 45 | 0.31 | ||

4 | 0.145 | −0.233 | 0.246 | −0.361 | 0.170 | 0.128 | 6.61 | 1, 44 | 0.014 | |

Duration | 1 | 0.104 | 0.011 | 0.011 | 0.51 | 1, 47 | 0.48 | |||

2 | 0.145 | −0.067 | 0.014 | 0.003 | 0.13 | 1, 46 | 0.72 | |||

3 | 0.152 | −0.041 | −0.038 | 0.014 | 0.001 | 0.02 | 1, 45 | 0.88 | ||

4 | 0.107 | 0.008 | −0.030 | 0.328 | 0.120 | 0.106 | 5.16 | 1, 44 | 0.028 | |

Mean Velocity | 1 | 0.155 | 0.024 | 0.024 | 1.14 | 1, 47 | 0.29 | |||

2 | 0.110 | 0.074 | 0.028 | 0.003 | 0.16 | 1, 46 | 0.69 | |||

3 | 0.083 | −0.032 | 0.155 | 0.036 | 0.008 | 0.39 | 1, 45 | 0.54 | ||

4 | 0.133 | −0.086 | 0.146 | −0.367 | 0.168 | 0.132 | 6.81 | 1, 44 | 0.012 | |

N Steps | 1 | −0.259 | 0.067 | 0.067 | 3.31 | 1, 47 | 0.075 | |||

2 | 0.022 | −0.463 | 0.202 | 0.135 | 7.63 | 1, 46 | 0.008 | |||

3 | 0.100 | −0.162 | −0.439 | 0.270 | 0.068 | 4.10 | 1, 45 | 0.049 | ||

4 | 0.055 | −0.114 | −0.431 | 0.327 | 0.375 | 0.105 | 7.21 | 1, 44 | 0.010 | |

TUG- SIT-TO-STAND | ||||||||||

Mean Pitch Vel (i–iii) | 1 | 0.101 | 0.010 | 0.010 | 0.47 | 1, 47 | 0.50 | |||

2 | 0.338 | −0.383 | 0.100 | 0.090 | 4.51 | 1, 46 | 0.039 | |||

3 | 0.240 | −0.378 | −0.007 | 0.100 | <0.001 | 0.001 | 1, 45 | 0.98 | ||

4 | 0.304 | −0.344 | −0.005 | 0.295 | 0.186 | 0.086 | 4.55 | 1, 44 | 0.039 | |

Max Pitch Vel (i–ii) | 1 | 0.227 | 0.052 | 0.052 | 2.51 | 1, 47 | 0.12 | |||

2 | 0.373 | −0.235 | 0.086 | 0.034 | 1.67 | 1, 46 | 0.20 | |||

3 | 0.371 | −0.243 | 0.012 | 0.086 | <0.001 | 0.002 | 1, 45 | 0.961 | ||

4 | 0.336 | −0.210 | 0.014 | 0.290 | 0.169 | 0.083 | 4.29 | 1, 44 | 0.044 | |

Mean Pitch Acc (i–ii) | 1 | 0.036 | 0.001 | 0.001 | 0.06 | 1, 47 | 0.81 | |||

2 | 0.201 | −0.266 | 0.045 | 0.043 | 2.05 | 1, 46 | 0.16 | |||

3 | 0.162 | −0.411 | 0.214 | 0.061 | 0.016 | 0.75 | 1, 45 | 0.39 | ||

4 | 0.116 | −0.366 | 0.217 | 0.385 | 0.207 | 0.146 | 7.94 | 1, 44 | 0.007 | |

Duration (i–iii) | 1 | 0.091 | 0.008 | 0.008 | 0.39 | 1, 47 | 0.54 | |||

2 | 0.165 | −0.119 | 0.017 | 0.009 | 0.40 | 1, 46 | 0.53 | |||

3 | 0.144 | −0.197 | 0.115 | 0.022 | 0.005 | 0.21 | 1, 45 | 0.649 | ||

4 | 0.103 | −0.157 | 0.118 | 0.344 | 0.138 | 0.117 | 5.83 | 1, 44 | 0.020 | |

TUG-WALK | ||||||||||

RMS Acc AP | 1 | 0.118 | 0.014 | 0.014 | 0.65 | 1, 47 | 0.43 | |||

2 | 0.272 | −0.248 | 0.052 | 0.038 | 1.80 | 1, 46 | 0.19 | |||

3 | 0.333 | −0.023 | −0.332 | 0.091 | 0.039 | 1.87 | 1, 45 | 0.18 | ||

4 | 0.290 | 0.018 | −0.329 | 0.357 | 0.217 | 0.126 | 6.94 | 1, 44 | 0.012 | |

N Steps | 1 | 0.024 | 0.001 | 0.001 | 0.03 | 1, 47 | 0.87 | |||

2 | −0.060 | 0.136 | 0.012 | 0.011 | 0.52 | 1, 46 | 0.48 | |||

3 | −0.057 | 0.148 | −0.017 | 0.012 | <0.001 | 0.005 | 1, 45 | 0.95 | ||

4 | −0.115 | 0.203 | −0.013 | 0.483 | 0.243 | 0.231 | 13.10 | 1, 44 | 0.001 | |

Duration | 1 | 0.124 | 0.015 | 0.015 | 0.71 | 1, 47 | 0.40 | |||

2 | 0.027 | 0.155 | 0.030 | 0.015 | 0.69 | 1, 46 | 0.41 | |||

3 | 0.018 | 0.120 | 0.051 | 0.031 | 0.001 | 0.04 | 1, 45 | 0.84 | ||

4 | −0.040 | 0.176 | 0.055 | 0.483 | 0.262 | 0.231 | 13.48 | 1, 44 | 0.001 | |

TUG-TURN 2 | ||||||||||

Max Yaw Vel | 1 | −0.136 | 0.019 | 0.019 | 0.87 | 1, 47 | 0.36 | |||

2 | −0.167 | 0.049 | 0.020 | 0.001 | 0.07 | 1, 46 | 0.80 | |||

3 | −0.178 | 0.007 | 0.062 | 0.021 | 0.001 | 0.06 | 1, 45 | 0.80 | ||

4 | −0.124 | −0.045 | 0.058 | −0.453 | 0.224 | 0.203 | 11.23 | 1, 44 | 0.002 | |

Mean Yaw Acc (i–ii) | 1 | −0.145 | 0.021 | 0.021 | 0.99 | 1, 47 | 0.33 | |||

2 | −0.051 | −0.153 | 0.035 | 0.014 | 0.67 | 1, 46 | 0.42 | |||

3 | −0.061 | −0.193 | 0.059 | 0.037 | 0.001 | 0.06 | 1, 45 | 0.81 | ||

4 | 0.007 | −0.259 | 0.055 | −0.573 | 0.362 | 0.325 | 21.88 | 1, 44 | <0.001 | |

Mean Yaw Acc (ii–iii) | 1 | 0.300 | 0.090 | 0.090 | 4.55 | 1, 47 | 0.038 | |||

2 | 0.353 | −0.086 | 0.094 | 0.005 | 0.23 | 1, 46 | 0.64 | |||

3 | 0.331 | −0.169 | 0.123 | 0.100 | 0.005 | 0.26 | 1, 45 | 0.61 | ||

4 | 0.294 | −0.135 | 0.126 | 0.302 | 0.190 | 0.090 | 4.79 | 1, 44 | 0.034 | |

Duration | 1 | 0.459 | 0.210 | 0.210 | 12.26 | 1, 47 | 0.001 | |||

2 | 0.460 | −0.001 | 0.210 | <0.001 | <0.001 | 1, 46 | 0.99 | |||

3 | 0.453 | −0.026 | 0.036 | 0.211 | <0.001 | 0.03 | 1, 45 | 0.87 | ||

4 | 0.411 | 0.014 | 0.039 | 0.349 | 0.331 | 0.121 | 7.75 | 1, 44 | 0.008 | |

TUG-STAND-TO-SIT | ||||||||||

Range Pitch Vel (i–ii) | 1 | −0.331 | 0.109 | 0.109 | 5.64 | 1, 47 | 0.022 | |||

2 | −0.297 | −0.054 | 0.111 | 0.002 | 0.09 | 1, 46 | 0.76 | |||

3 | −0.259 | 0.084 | −0.204 | 0.126 | 0.015 | 0.74 | 1, 45 | 0.40 | ||

4 | −0.219 | 0.045 | −0.207 | −0.339 | 0.239 | 0.113 | 6.41 | 1, 44 | 0.015 | |

Range Pitch Vel (ii–iii) | 1 | −0.408 | 0.166 | 0.166 | 9.16 | 1, 47 | 0.004 | |||

2 | −0.388 | −0.031 | 0.167 | 0.001 | 0.03 | 1, 46 | 0.86 | |||

3 | −0.314 | 0.244 | −0.406 | 0.225 | 0.058 | 3.30 | 1, 45 | 0.076 | ||

4 | −0.280 | 0.212 | −0.408 | −0.279 | 0.302 | 0.077 | 4.74 | 1, 44 | 0.035 | |

SD Pitch Vel (i–iii) | 1 | −0.401 | 0.161 | 0.161 | 8.83 | 1, 47 | 0.005 | |||

2 | −0.333 | −0.109 | 0.168 | 0.007 | 0.40 | 1, 46 | 0.53 | |||

3 | −0.272 | 0.119 | −0.337 | 0.208 | 0.040 | 2.22 | 1, 45 | 0.14 | ||

4 | −0.235 | 0.083 | −0.339 | −0.308 | 0.302 | 0.094 | 5.80 | 1, 44 | 0.020 | |

Mean Pitch Acc (i–ii) | 1 | 0.196 | 0.038 | 0.038 | 1.84 | 1, 47 | 0.18 | |||

2 | 0.101 | 0.154 | 0.053 | 0.015 | 0.69 | 1, 46 | 0.41 | |||

3 | 0.038 | −0.076 | 0.339 | 0.094 | 0.041 | 1.97 | 1, 45 | 0.17 | ||

4 | 0.004 | −0.043 | 0.341 | 0.286 | 0.174 | 0.081 | 4.21 | 1, 44 | 0.046 | |

Mean Pitch Acc (ii–iii) | 1 | −0.440 | 0.194 | 0.194 | 11.04 | 1, 47 | 0.002 | |||

2 | −0.319 | −0.195 | 0.217 | 0.023 | 1.35 | 1, 46 | 0.25 | |||

3 | −0.290 | −0.088 | −0.158 | 0.226 | 0.009 | 0.50 | 1, 45 | 0.48 | ||

4 | −0.245 | −0.132 | −0.161 | −0.376 | 0.365 | 0.140 | 9.46 | 1, 44 | 0.004 | |

Mean Acc AP (i–iii) | 1 | −0.320 | 0.102 | 0.102 | 5.25 | 1, 47 | 0.027 | |||

2 | −0.176 | −0.233 | 0.136 | 0.033 | 1.74 | 1, 46 | 0.19 | |||

3 | −0.142 | −0.109 | −0.183 | 0.148 | 0.012 | 0.61 | 1, 45 | 0.44 | ||

4 | −0.097 | −0.152 | −0.186 | −0.372 | 0.285 | 0.137 | 8.25 | 1, 44 | 0.006 | |

SD Acc AP (i–iii) | 1 | −0.279 | 0.078 | 0.078 | 3.89 | 1, 47 | 0.055 | |||

2 | −0.233 | −0.075 | 0.081 | 0.003 | 0.17 | 1, 46 | 0.68 | |||

3 | −0.174 | 0.143 | −0.322 | 0.118 | 0.036 | 1.82 | 1, 45 | 0.19 | ||

4 | −0.136 | 0.107 | −0.324 | −0.315 | 0.216 | 0.098 | 5.39 | 1, 44 | 0.025 |

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

O’Brien, M.K.; Hidalgo-Araya, M.D.; Mummidisetty, C.K.; Vallery, H.; Ghaffari, R.; Rogers, J.A.; Lieber, R.; Jayaraman, A.
Augmenting Clinical Outcome Measures of Gait and Balance with a Single Inertial Sensor in Age-Ranged Healthy Adults. *Sensors* **2019**, *19*, 4537.
https://doi.org/10.3390/s19204537

**AMA Style**

O’Brien MK, Hidalgo-Araya MD, Mummidisetty CK, Vallery H, Ghaffari R, Rogers JA, Lieber R, Jayaraman A.
Augmenting Clinical Outcome Measures of Gait and Balance with a Single Inertial Sensor in Age-Ranged Healthy Adults. *Sensors*. 2019; 19(20):4537.
https://doi.org/10.3390/s19204537

**Chicago/Turabian Style**

O’Brien, Megan K., Marco D. Hidalgo-Araya, Chaithanya K. Mummidisetty, Heike Vallery, Roozbeh Ghaffari, John A. Rogers, Richard Lieber, and Arun Jayaraman.
2019. "Augmenting Clinical Outcome Measures of Gait and Balance with a Single Inertial Sensor in Age-Ranged Healthy Adults" *Sensors* 19, no. 20: 4537.
https://doi.org/10.3390/s19204537