A new measure of trip risk integrating minimum foot clearance and dynamic stability across the swing phase of gait

Minimum toe clearance (MTC) is thought to quantify the risk of the toe contacting the ground during the swing phase of gait and initiating a trip, but there are methodological issues with this measure and the risk of trip-related falls has been shown to also be associated with gait speed and dynamic stability. This paper proposes and evaluates a new measure, trip risk integral (TRI), that circumvents many issues with MTC as typically calculated at a single point by considering minimum foot clearance across the entire swing phase and taking into account dynamic stability to estimate risk of falling due to a trip rather than risk of the foot contacting the floor. Shoes and floor surfaces were digitized and MTC and TRI calculated for unimpaired younger (N = 14, age = 26 ± 5), unimpaired older (N = 14, age = 73 ± 7), and older adults who had recently fallen (N = 11, age = 72 ± 5) walking on surfaces with no obstacles, visible obstacles, and hidden obstacles at slow, preferred, and fast gait speeds. MTC and TRI had significant (F ≥ 5, p ≤ 0.005) but differing effects of gait speed and floor surface. As gait speed increased (which increases risk of trip-related falls) MTC indicated less and TRI greater risk, indicating that TRI better quantifies risk of falling due to a trip. While MTC and TRI did not differ by subject group, strong speed-related effects of TRI (F ≥ 8, p ≤ 0.0007) resulted in improved TRI for fallers due to their slower self-selected preferred gait. This demonstrates that slower gait is both an important covariate and potential intervention for trip-related falls.