# Outdoor Walking Classification Based on Inertial Measurement Unit and Foot Pressure Sensor Data

## TL;DR

This study compares sensors and machine learning models to automatically classify different walking conditions like stairs or slopes.

## Contribution

The paper introduces a comparison of sensor types and machine learning approaches for classifying outdoor walking conditions.

## Key findings

- Deep learning models using lower-limb IMUs with gait segmentation achieved the highest classification performance (F1=0.89).
- Combining sensor modalities and gait segmentation improved machine learning model performance significantly (p<0.01).
- Deep learning models performed well without gait segmentation, reducing reliance on gait event identification algorithms.

## Abstract

(1) Background: Navigating surfaces during walking can alter gait patterns. This study aims to develop tools for automatic walking condition classification using inertial measurement unit (IMU) and foot pressure sensors. We compared sensor modalities (IMUs on lower-limbs, IMUs on feet, IMUs on the pelvis, pressure insoles, and IMUs on the feet or pelvis combined with pressure insoles) and evaluated whether gait cycle segmentation improves performance compared to a sliding window. (2) Methods: Twenty participants performed flat, stairs up, stairs down, slope up, and slope down walking trials while fitted with IMUs and pressure insoles. Machine learning (ML; Extreme Gradient Boosting) and deep learning (DL; Convolutional Neural Network + Long Short-Term Memory) models were trained to classify these conditions. (3) Results: Overall, a DL model using lower-limb IMUs processed with gait segmentation performed the best (F1=0.89). Models trained with IMUs outperformed those trained on pressure insoles (p<0.01). Combining sensor modalities and gait segmentation improved performance for ML models (p<0.01). The best minimal model was a DL model trained on IMU pelvis + pressure insole data using sliding window segmentation (F1=0.83). (4) Conclusions: IMUs provide the most discriminative features for automatic walking condition classification. Combining sensor modalities may be helpful for some model architectures. DL models perform well without gait segmentation, making them independent of gait event identification algorithms.