The prosthesis Fox used for the Marathon of Hope was designed by prosthetist Ben Speicher. Speicher adapted the conventional walking prosthesis, using a steel knee joint that operated much like a hinge (the Otto Bock 3R17). The leg was attached by suction and a series of belts; an elastic strap was added to help extend the leg forward. At about 4 kg, the prosthesis was heavy compared to the lightweight running prostheses used today.
Fast forward to 1975 and the year an inventor named Ysidro M. Martinez took things a major step further by creating a below-the-knee prosthesis that avoided some of the problems associated with conventional artificial limbs. Instead of replicating the natural limb with articulated joints in the ankle or foot which tended to lead to poor gait, Martinez, an amputee himself, took a theoretical approach in his design. His prosthesis relies on a high center of mass and is light in weight to facilitate acceleration and deceleration and reduce friction. The foot is also considerably shorter to control acceleration forces, further reducing the friction and pressure.
A single leg prosthetic for below the ..
New advances to keep an eye involve the growing use of 3-D printing, which has allowed for the fast, precise manufacturing of artificial limbs that traditionally have been custom-built by hand. The U.S. government’s National Institutes of Health has recently established the 3D Print Exchange program as a way to provide researchers and students with the necessary modeling and software tools to fabricate prosthetics using 3D .
The Genium is the intelligent leg prosthesis system
Unfortunately, Fox died before Martel could develop a better running prosthesis. However, in February 1982, Martel and his team received a $17,000 research grant from The War Amps of Canada to build an improved running prosthesis. The research team (Martel, Hubert de Bruin, head of biomedical engineering, and mechanical technologist Edwin Iler) eventually developed and tested a lighter leg which used a commercial carbon graphite polycentric-axis knee joint, a standard foot, an improved version of Terry’s failed spring-loaded mechanism and a pneumatic shock absorber. The spring shaft compressed upon heel strike, reducing the impact to the residual limb. The heel-strike compression also shortened the leg slightly, lowering the runner’s centre of gravity. At toe-off, the compressed spring released its stored energy, which helped propel the prosthesis and the runner forward. The improvements would have made it easier for Fox to run, and would have eliminated the need for the hop-skip style of running that he used.
Custom leg prosthetic hits the runway at Fashion Week - blogTO
Another problem facing Fox was something known as a slow “swing-through.” Runners normally use their quadriceps to quickly propel their lower legs forward, before the heel strikes the ground. For an above-knee amputee, that task has to be performed by the hip muscles. With a conventional prosthesis, the swing time was slow and active knee flexion impossible. An amputee runner therefore had to wait for the leg to swing forward to full extension before weight could be applied, allowing him to vault over the straightened leg. Although Fox’s prosthesis incorporated a strong elastic strap to speed up the swing-through phase, it was still very slow. This resulted in his “hop and skip” style of running— hopping on his sound leg while he waited for his prosthetic leg to swing through. This hop not only allowed time for the prosthesis to extend, but also helped cushion the blow to his residual limb in its rigid prosthetic socket. The technique was hard on the body, particularly on the hip joint of his sound left leg.
onto a wearer's existing prosthesis; ..
One of the biggest problems for an amputee runner like Fox was that a conventional prosthesis was not designed to absorb the impact generated at heel strike by running. Runners can hit the ground with up to four times the force of their body weight — about two times the force compared to someone walking. That force is normally absorbed with knee flexion, and by the quadriceps and calf muscles. In an able-bodied runner, the foot also helps to absorb shock and return some energy to the body. Fox’s prosthetic foot, which was made of wood and rubber, could not perform either function. Fox’s prosthetic leg was not designed to absorb the impact of running. He and Speicher experimented with a pogo stick design, using a motorcycle shock absorber, but they didn’t like the result and ended up abandoning it prior to the marathon.