SPRINTER’S KING (Running Foot)
PATENT: ROADRUNNERFOOT ENGINEERING SRL
INVENTOR: BONACINI DANIELE
AIMS OF THE INNOVATION:
THE NEW SPRINTING FOOT WANTS TO PROMOTE SPORT PRACTICE IN NEW USERS, ALLOWING A MINOR ENERGY CONSUPTION
AND EFFORT, AND WANTS TO INCREASE AGONIST ATHLETE PERFORMANCE.
Design aims were:
- to eliminate the negative force component (Fx) opposite to forward direction during foot's loading, this is a functional limits of commercially feet;
- to have same functionality of soleus-Achilles’ tendon complex of the sound limb which gives to the limb its 90% of elasticity;
-to set the points of maximum peak of vertical force (Fz) and forward force (Fx) during the foot’s contact to the ground (Mid-stance), when femur is
- perpendicular to the ground, to allow user to take advantage of foot’s elastic response;
a better vertical force and forward force modulus ratio: the stride is wider and knee trajectory is closer to the ground
CINETIC ANALYSIS OF RUNNING AND COMMERCIALLY FEET PERFORMANCES
Cinetic analysis of 3 below knee amputee and 3 normal athletes, allowed to define functional limits of
commercially feet and to set specification and aims of the design.
After taking anthropometric measurements and subject and prosthesis markerization it’s possible to acquire running
with an optoelectronic system (Vicon) and a force platform (Kistler). Data elaborations allow to see all temporal –
spatial parameters (stride length, cadence, velocity, etc.), joints angles graphs and the Ground Reaction Forces
diagram, for both prosthetic and sound limb.
INITAIL CONTACT, previews MID STANCE MID STANCE REAL TOE OFF
Foot’s elastic response: when a normal person go through the Mid-stance phase, Fx and Fz curve is raising, that is the athlete is able to use the maximum force when needed. For
an amputee, instead, during Mid-stance Fx and Fz curve goes down and that’s why amputee stride is shorter! Ground reaction forces (Fx and Fz) are lower in value and
asimmetrical between sound and prosthetic limb. For normals Fz goes from 2600 to 3500 N, for amputee: concerning sound limb, Fz’s about 2500- 3200, while concerning prosthetic
leg goes from 2400 to 2550 N; Fx for amputee athletes is 250-300 N, about half normal athletes Fx (450-600 N).
Foot’s loading phase is to high: it should end as soon as knee center of rotation of sound swing limb overtake prosthetic knee center of rotation (yellow dot).
Foot’s reaction, that is energy releasing, of prosthesis should be higher in order to be comparable with the sound limb. During Toe-Off foot doesn’t provide a safe support,
therefore stride length between the two limb, is different.
During loading phase the foot deflects, the vertex of the posterior curve goes down and back, due to rigidity of foot’s sections: the linking line between ground contact point and heel,
rotates 5° clockwise and the rotation generate a negative force that push backward (increasing hip muscles effort).
All these limits lead to a shorter stride and velocity of prosthetic limb.
The INNOVATIVE MORPHOLOGY of Sprinter’s King consists in:
1- the inclination between virtual V° metatarsus and virtual heel, allow a plantar-flexion real close to
normal ankle one
2- the fixing point of the foot and the inclination of the bracket were designed to have the same
functionality of triceps surae muscles and tendons
3- the curve of artificial ankle reduce elastic response time to increase foot’s efficiency
4- Variable thickness in different foot’s sections determinate different stiffness in order to provide
comfortable limb cinematic
5- The forefoot has the same transversal section of the human foot, therefore provide a safe support
during contro-lateral limb swing phase.
FOOT SIMULATIONS DURING WORKING
Elasto-cinematic and structural performances of Sprinter’s King foot were been evaluated in
comparison with human foot behavior and other competitor’s feet (Cheetah – Ossur, Spriglite –
Otto Bock), through FEM analysis.
Thanks to motion capture acquisitions of amputee running it was possible to analyze joint cinematic
and GRFs which allowed to set up the FEM simulations for Sprinter’s King and other commercially feet.
TARGETS ACHIEVED:
TESTING ON EQUIPMENTS AND PEOPLE:
This new generation feet comply with ISO 10328, concerning prosthetic
components. A sportive aids is not included in this kind of standard, therefore
we adapted the procedures: SK exceed 7000N during ultimate strength test, where
the standards prescribes 3360 N, and excedeed also the cycle test with a cycle force of
3000N for 300.000 cycles, like one year daily training (3h) at maximum performance,
after that the foot must be changed (the standard prescribes 1330 N for 2000.000
cycles).
NO more backwards force component during loading phase.
Fx and Fz components gives more balance and stability to the athlete during running. Infact the propulsive force push exactly during Mid-stance. Maximum value of Fx is higher
than other commercially feet. Fz/Fx ratio is smaller, to promote pushing in forward direction. Fz value is higher.
Prosthetic limb cinematic is closer to sound limb: stride length is identical to the sound limb one.