Biomechanics of the human walk-to-run gait transition in persons with unilateral transtibial amputation

Propulsive force production (indicative of intrinsic force-length-velocity characteristics of the plantar flexor muscles) has been shown to be a major determinant of the human walk-to-run transition. The purpose of this work was to determine the gait transition speed of persons with unilateral transtibial amputation donning a passive-elastic prosthesis and assess whether a mechanical limit of their intact side plantar flexor muscles is a major determinant of their walk-to-run transition. We determined each individual׳s gait transition speed (GTS) via an incremental protocol and assessed kinetics and kinematics during walking at speeds 50%, 60%, 70%, 80%, 90%, 100%, 120%, and 130% of that gait transition speed (100%:GTS). Unilateral transtibial amputees transitioned between gaits at significantly slower absolute speeds than matched able-bodied controls (1.73±0.13 and 2.09±0.05 m/s respectively, p<0.01). Peak anterior-posterior propulsive force increased with speed in controls until 100% of the preferred gait transition speed and decreased at greater speeds. A significant decrease in anterior-posterior propulsive force production was found at 120%GTS (110%: 0.27±0.04>120%: 0.23±0.05BW, p<0.05). In contrast, amputee subjects' intact side generated significantly higher peak anterior-posterior propulsive forces while walking at speeds above their preferred gait transition speed (100%: 0.28±0.04<110%: 0.30±0.04BW, p<0.05). Changes in propulsive force production were found to be a function of changes in absolute speed, rather than relative to the walk-to-run transition speed. Therefore, the walk-to-run transition in unilateral transtibial amputees is not likely dictated by propulsive force production or the force-length-velocity characteristics of the intact side plantar flexor muscles.