Spring-mass behavioural adaptations to acute changes in prosthetic blade stiffness during submaximal running in unilateral transtibial prosthesis users

Background: Individuals with lower-limb amputation can use running specific prostheses (RSP) that store and then return elastic energy during stance. However, it is unclear whether varying the stiffness category of the same RSP affects spring-mass behaviour during self-selected, submaximal speed running in individuals with unilateral transtibial amputation. Research question: The current study investigates how varying RSP stiffness affects limb stiffness, running per-formance, and associated joint kinetics in individuals with a unilateral transtibial amputation. Methods: Kinematic and ground reaction force data were collected from eight males with unilateral transtibial amputation who ran at self-selected submaximal speeds along a 15 m runway in three RSP stiffness conditions; recommended habitual stiffness (HAB) and, following 10-minutes of familiarisation, stiffness categories above (+1) and below (-1) the HAB. Stance-phase centre of mass velocity, contact time, limb stiffness' and joint/RSP work were computed for each limb across RSP stiffness conditions. Results: With increased RSP stiffness, prosthetic limb stiffness increased, whilst intact limb stiffness decreased slightly (p<0.03). Centre of mass forward velocity during stance-phase (p<0.02) and contact time (p<0.04) were higher in the intact limb and lower in the prosthetic limb but were unaffected by RSP stiffness. Intact limb hip joint positive work increased for both the +1 and-1 conditions but remained unchanged across conditions in the prosthetic limb (p<0.02). Significance: In response to changes in RSP stiffness, there were acute increased mechanical demands on the intact limb, reflecting a reliance on the intact limb during running. However, overall running speed was unaffected, suggesting participants acutely adapted to an RSP of a non-prescribed stiffness.

Automated summary

This study investigates how varying the stiffness of running specific prostheses (RSP) affects limb stiffness, running performance, and joint kinetics in individuals with unilateral transtibial amputation. The results show that increasing RSP stiffness increases prosthetic limb stiffness and slightly decreases intact limb stiffness. Intact limb forward velocity during stance-phase and contact time are higher, while prosthetic limb values are lower, but these are not affected by RSP stiffness. Intact limb hip joint positive work increases for both higher and lower stiffness conditions, while prosthetic limb work remains unchanged. The results indicate an acute mechanical demand on the intact limb in response to changes in RSP stiffness, but overall running speed is unaffected.