"It's completely passive," Morgenroth explains. However, the blades have competitive advantages. Once a runner on blades reaches peak speed, one possible advantage is the ability to move the prostheses faster and with less effort—because the blades weigh less than the lower legs and feet of a competition. Also, runners using blades may be able to change direction more quickly because they do not have any contact with the ground during a turn.
Overall, though, the main advantage of using blades is that they do not impede movement in any way, which means that runners can achieve higher speeds and cover greater distances than if they were using normal prosthetic limbs.
There are two types of blades: fixed-base and swing-based. A fixed-base blade remains in a single position throughout the race, while a swing-based blade moves back and forth like a pendulum. Since runners using fixed-base blades cannot change their direction, they are not suitable for events where turning is necessary (such as road races). Individuals who use swing-based blades can change direction easily but cannot go as fast as those who are using normal legs.
Blades are used in sports such as archery, shooting, fencing, and wheelchair racing.
They discovered that the design of the prostheses made a significant difference in speed, with runners hitting maximum speeds roughly 8% faster in "J-shaped" prosthesis (imagine the sleek carbon-fiber blades Oscar Pistorius used in his memorable 2012 Olympic sprint) than in "C-shaped" prostheses. The study also revealed that blade runners were capable of increasing their speed over long distances.
The research was conducted by Professors David Zwemke and Andrew Leong at the University of Windsor in Canada. They studied the running styles of five male patients who had been using J-shaped prostheses since having their legs amputated as children. The researchers filmed the amputees as they ran on a treadmill at different speeds and analyzed their footfalls using motion-capture technology. They found that the prosthetic limbs provided more lift per step at takeoff and landed with less impact at heel strike, allowing the users to cover greater distances before reaching max speed.
Blade runners are so named because of the design of their prostheses, which resemble two curved blades that extend down from beneath the knee joint. This allows for more natural movement and increases stability when running on uneven surfaces. Patients report feeling more connected to their bodies after replacing their rigid metal knees with these devices.
However, not all prosthetic legs are created equal. There are two main types: body-powered and functional.
2-blade propellers are somewhat more efficient in general. If these variables remain constant, the efficiency of a propeller decreases as the number of blades increases. However, when engine power grows, more blades are usually necessary to properly use the extra power and generate thrust. 4-, 6-, and 8-blade props are common today.
The advantage of using a 2-blade prop is that it's cheaper to manufacture and easier to maintain. A 4- or 5-blade prop will work just as well from an engineering point of view, but may be more expensive to produce due to more complex manufacturing processes and materials required. An 8-blade prop will typically have thicker blades which are harder to make and stronger but also cost more to produce.
There is no real advantage to having more than eight blades on a prop unless you're making a custom-built prop. Most aircraft engines can handle up to 12-14 blades without any problems - larger props tend to come from turbine engines rather than piston ones because they require more torque at low speeds.
However, there are some disadvantages to having more than eight blades on a prop. First of all, it gets harder to make each blade fit accurately on props with more than eight blades. Secondly, more blades means more weight, which reduces efficiency yet again. Finally, making sure all the blades are balanced correctly becomes more difficult as the number of blades increases.
A fuller's principal function is to lighten the blade; lighter swords are easier and faster to handle. Variations in fuller qualities may also have an impact on the weight balance and associated features of the blade. For example, a sword with more robust fuller bones will be heavier and less likely to tip over if you hit something.
Some swords have markings indicating where to file down the blade to produce a finer point. These are called "finesse points". The term comes from the fact that they are useful for finishing cuts, not thrusting. They are generally found on weapons intended for use by non-combatants, such as courtiers or guardsmen. Guards used finesse points because they were less likely to cause injury when defending themselves or their masters' families/property.
Some swords have markings indicating where to grind the edge of the blade so it can be used as a cutting tool as well as a weapon. These are called "edge tools". Edge tools can be used for cutting ropes, leather, etc. They are generally found on weapons intended for use by soldiers on the battlefield. The term "edge" does not refer to the edge itself but rather the entire surface from heel to tip. Thus, an "edge" sword has a flat surface at each side of the blade where filing or grinding would take place.