Minimum Foot Clearance Prediction in Stroke Survivors: A Transformer-Based Approach

A decrease in Minimum Foot Clearance (MFC), which represents the minimum vertical distance of the foot from the ground surface during the swing phase of the gait cycle, is one of the primary contributors to tripping-related falls among people with stroke. Accurate prediction of upcoming MFC values, understanding their potential range, and evaluating whether future values will fall within the variability of actual MFC values are crucial for early fall risk assessment. This work proposes a new Transformer model for predicting multistep MFC values in stroke survivors collected from the affected lower-limb during walking on a treadmill utilizing a two-head self-attention mechanism. We introduce a data-driven conditional post-normalization projection approach to enhance the performance of multistep prediction for MFC values. In addition, we introduce a statistical moment-matching loss function during training to account for significant data variability, such as that observed in individuals with stroke. We compare the performance of our model with two other deep learning models. Our findings indicate that the Transformer model training is faster and achieves an average Mean Absolute Error (MAE) of approximately 0.0035, Maximum Absolute Error (MaxAE) of 0.0085 and a Root Mean Square Error (RMSE) of 0.0043, using the leave-one-out cross-validation (LOOCV) method. The highest prediction within the upper bound (PWUB) of around 89% is achieved with self-attention LSTM model. The main contribution of our work is to identify when an individual stroke survivor is at increased risk of tripping-related falls due to a lower MFC value in their affected lower limb.