FootNet architecture.

FootNet takes the distal tibia anteroposterior velocity, ankle plantar/dorsiflexion angle and the foot COM anteroposterior and vertical velocities as input and produces a sequence of probabilities of non-contact (0) and contact (1). Note that the input features are first standardised (z scores), 0-padded at the start of the sequence to a standard length of 200 data-points and concatenated into a 1x200x4 array where 1 is the number of cycles, 200 is the number of timepoints and 4 is the number of input features. Zero padding was added to batch the training cases and 200 was selected as a sufficient number of timepoints to accommodate a stride cycle at any of the tested speeds. The padding is ignored during training, hence the 0.5 values at the beginning of the output sequence.