Re: What is the science behind sports safety equipment?

Hi Nathan.

I am answering this question from a physicist's and sports participant's point of view. You may also seek the input of a athlete trainer, physical therapist, or a orthopedic specialist.

Many of human endeavors include the possiblilty of injury. Sports, in particular, can be especially dangerous when the game involves collisions between players or players and equipment of the game. All collisions can be viewed in terms of momentum or force and energy imparted.

Sports safety equipment is designed to redirect momentum, spread pressure, absorb energy, and/or restrict torque and provide support.

Here are some examples of particular sports equipment. Using the above criteria, I think most any piece of equipment can be qualitatively analyzed. My criteria above is by no means intended to be all inclusive.

Let's discuss a shin guard. Shin guards are common in soccer, baseball for catchers and umpires, and all forms of hockey. A shin guard is designed to take a shot from an object with a small cross section and distribute the force over the surface of the guard. Take a field or ice hockey stick for example. The stick typically has a small width on any face. The typical thickness might be about 1 inch. If an unprotected field hockey player is slashed in the shin by an opponent's stick all the force of the blow will be directed on any area of rough 1 inch by the width of the shin bone. This may be enough a concentrated force to break bone and certainly could leave a nasty welt and bruise. However, if the player is wearing a shin guard, the force will be distributed throughout the area of shin guard. The force on the underlying leg will be spread out and is less likely to cause injury in the form of a bruise.

Another good example of a piece of sports equipment that redistributes pressure more evenly is a helmet. A shot to the head of 300 pounds concentrated in an area of 2 or 3 square inches will likely cause a severe bruise or skull fracture and the rebounding of the brain within the skull will cause a severe concussion. This type of hit could even be deadly if located to the temple, ear, or base of the skull. A helmet should be designed to redistribute the force of the collision to nearly the full surface area of the head. A helmet will not necessarily reduce the risk of concussion, but they do greatly reduce the risk of local trauma.

Shoulders are particularly vulnerable to bruising and dislocation. Shoulder pads help absorb energy and spread the area of the applied force to the size of the shouler pad. The "pop" a football coach loves to hear from shoulder pad collisions comes from the conversion of kinetic energy to sound energy.

Knee braces with hinged metal rods are designed to protect the knee from lateral and anterior hyerextension that can lead to lateral cruciate or anterior cruciate ligament damage. The knees braces simply limit the range of motion on the knee joint. The torque is restricted, however the force is still the same and sometimes the lower part of the leg is injured instead of the knee.

Many athletes turn to tape jobs and elastic braces for joint protection. Taped ankles or wrists are restricted in their range of motion and are therefore less likely to be hyperextended. Elastic braces are supposed to give additional joint support to tendons but many sports trainers and doctors believe that an over dependence on elastic braces leads to weaker joints or the use of the afflicted joint when the athlete really should be resting. Tape and elastic braces are by no means without risk.

Sincerely,

Tom "Boom Boom" Cull