Bio Mechanics

By Amanda Brunner

Manz82400@yahoo.com

The Knee  



   The knee joint is essential in everyday activities and plays a big role in mountain biking.  The knee is the joint most vulnerable to severe injuries.  First lets get into how the knee joint is held together.


   The two major bones holding your knee together are the femur and the tibia.  The patella is a small sesame-shaped bone also known as the kneecap. The main function for this bone is to serve as a pulley for the quadriceps. The joint is made up of four major ligaments and a couple of smaller ligaments. Two of the four major ones are named the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL).  They are given this name because they cross each other and are located at the center of the knee.  An ACL tear is one of the major knee injuries many people sustain in many activities.  A torn ACL can either be left un-repaired if it is not torn completely.  In doing so, it will never be the same: It may be stable at times or could give out on a person while they are doing normal activities.  If it is torn all the way it can be reconstructed through tendon grafting.  If it is torn all the way do not let it go because as you constantly bear weight on it, it will get worse and worse and eventually it will no longer be operational.  Some signs and symptoms of a severe ACL injury is a loud "pop" at the time of the injury or a ripping noise that you will feel more that hear.  As time passes the knee will start to swell, there will be tenderness, muscle spasms around the joint, and the inability to bear weight on the leg.  Female athletes are more susceptible to ACL injuries than males.  The reason for this is due to the fluctuation of hormones during menstrual years.  The PCL is stronger than the ACL so it is not injured as often.

   The medial collateral ligament (MCL) and the lateral collateral ligament (LCL) are located in either side of the knee joint.  The MCL serves to protect the knee against inward force.  The LCL protects the knee against outward force.  The MCL is able to heal itself if it is not to severely torn.  Keeping off the leg for duration of time gives the ligament time to heal.  The LCL is rarely injured in isolation due to the fact that an outward force rarely happens.


   The knee joint is also made up of menisci (meniscus- singular).  These are two crescent shaped pieces of tough cartilage that are located between the ends of the femur and the tibia at the end of the knee.  The menisci serve to cushion the joint during impact.  When doctors first starting operating on the meniscus they would remove the entire pad causing an early onset of arthritis in the joint.  This in turn would end up causing the knee joint to no longer bend.  Removing part of the meniscus is not as severe but is also dangerous.  Considering the part that you injured is most likely the part that you use the most.  Cross suturing is the newest research on repairing the meniscus.  This, in my opinion, is the best alternative for repairing the knee. 


   Why is it more dangerous to ride a bike than to go jogging?  The fact is as your speed increases, your kinetic energy increases by a power of two.  This theory has the biggest influence on knee injuries and their relationship to speed.  When a person changes their speed from brisk walking to flying down a hill, their speed is then increased by a power of five, making their kinetic energy increase by a factor of twenty-five.  Therefore if you were to fall it would be twenty-five more times severe! With that said, the benefit of wearing protection becomes clear. 


   However, this isn't intended to shake your faith in mountain bike riding.  There are some strength exercises to help maintain a stronger joint.  The key is to strengthen the hamstring and quadriceps.  Strengthening the muscles surrounding the joint in turn strengthens the joint itself.  The best way to do this is to ride.  Put the bike on a high gear and ride at a low RPM.  Do this for seven to ten reps (pedals). Make a schedule and try to do this every other day giving the muscles time to heal the days in between.  If you don't allow them to heal it is possible to constantly rip the muscles (obviously doing them more harm than good.)  On the days that the weather is too foul for riding, go to the gym and do seven to ten reps of squats while holding a weight.


   Mountain biking is a great sport for people of all ages and a wonderful cardio vascular activity.  Just keep in mind that safety comes first.  Take care of your body and your body will take care of you.