Greater mediolateral required coefficient of friction reflects asymmetric gait control in individuals with unilateral transfemoral amputation.

Individuals with unilateral transfemoral amputation are at greater risk of falls than individuals without amputation, with slipping being a major contributing factor. The required coefficient of friction, defined as the minimum shoe-floor friction needed to prevent slipping, has been well studied in individuals without amputation but remains poorly understood in individuals with unilateral transfemoral amputation. Especially, its association with gait parameters in this population is unclear. This study investigated differences in resultant required coefficient of friction and its mediolateral and anteroposterior components between individuals with unilateral transfemoral amputation and individuals without amputation across multiple walking speeds, and examined their associations with spatial gait parameters. Thirty individuals with unilateral transfemoral amputation and 30 matched controls walked at eight fixed speeds (0.55-1.53 m/s) on an instrumented treadmill. Ground reaction forces were used to calculate required coefficient of friction and step parameters. At the time point corresponding to required coefficient of friction, the mediolateral component of required coefficient of friction was significantly greater in the intact limb than in the prosthetic limb across all walking speeds, indicating elevated mediolateral friction demand. Step width was negatively associated with mediolateral component of required coefficient of friction in the prosthetic limb, suggesting that mediolateral friction demand is modulated by base-of-support adjustments under prosthetic constraints. In contrast, associations between step parameters and the anteroposterior component were less consistent. These findings identify limb-specific mediolateral friction demands as a key feature of prosthetic gait and provide mechanistic insight into slip-related risk during human bipedal walking.