Fig 1.
Illustration of the calculated angle (β) between the longitudinal axis of the running-specific prosthesis (dashed blue line) and the peak resultant GRF vector (solid red arrow).
Fig 2.
Material testing setup with each running specific-prosthetic model.
Each running specific-prosthesis (RSP) was tested with the respective manufacturer’s rubber sole (Össur Cheetah Xtend prosthesis was equipped with an Össur Flex-Run’s sole), using our rotating base, and low-friction roller system. a) An Össur Flex-Run prosthesis (C-shaped) tested at 0°. b) A Freedom Innovations Catapult prosthesis (C-shaped) tested at α° (3 m/s). c) An Ottobock 1E90 Sprinter prosthesis (J-shaped) tested at neutral (0°). d) An Össur Cheetah Xtend prosthesis (J-shaped) tested at β° (6 m/s). h indicates prosthetic height.
Table 1.
The manufacturer recommended running-specific prosthesis (RSP) stiffness categories with the corresponding body mass for distance running and sprinting, plus the quantity of RSPs tested.
Fig 3.
Representative force-displacement profiles for running-specific prosthetic models at each testing angle.
Each running-specific prosthesis (RSP) is the manufacturer recommended stiffness category for a 70 kg distance runner. α3 and β3 indicate the measured angle between the RSP and peak resultant ground reaction force (GRF) vector while running 3 m/s using the C-shaped RSPs (Flex-Run and Catapult) and J-shaped RSPs (1E90 Sprinter and Cheetah Xtend), respectively. α6 and β6 indicate the measured angles between the RSP and peak resultant GRF vector while running 6 m/s using the C-shaped RSPs and J-shaped RSPs, respectively. a) The Flex-Run prosthesis at testing angles of 0°, α3, and α6, b) the Catapult prosthesis at testing angles of 0°, α3, and α6, c) the 1E90 Sprinter prosthesis at testing angles of 0°, β3, and β6, and d) the Cheetah Xtend prosthesis at testing angles of 0°, β3, and β6.
Fig 4.
Prescribed prosthetic stiffness.
The average stiffness (kN/m) of each running-specific prosthesis (RSP) as a function of the respective manufacturer’s recommended user body mass (kg) at running speeds of 3 m/s (a), and 6 m/s (b). The stiffness of each RSP was calculated using peak applied force magnitudes that simulated running 3 m/s (α3 and β3) and 6 m/s (α6 and β6). We then calculated displacement using the mean curvilinear force-displacement profiles with the appropriate applied force magnitudes. See S1–S4 Tables.
Table 2.
The manufacturer recommended average prosthetic stiffness across models based on running 3 m/s and 6 m/s.
All values include the rubber sole that comes with the prosthetic model, with the exception of the Össur Cheetah Xtend, which was equipped with the Össur Flex-Run’s rubber sole.