Biomechanics and the Olympics: Part VIII

In my opinion, one of the most difficult events in track and field is the hurdles.  To get an idea, try running as fast as you can and jumping over an imaginary object every 10 meters.  It's not easy to do, and even more difficult when you add in a 42 inch (106.7 cm) high hurdle for men and a 33 inch (83.8 cm) high hurdle for women.  It is a skill that requires speed, strength and flexibility.  What joint actions are required in order to clear a hurdle?

If you watch hurdling, some athletes lead with their right leg, and some lead with their left leg, but it is always the same leg that leads.  In the picture above, the athlete in the middle uses her right leg to push off, and her left leg to land on.  We can call the right leg the propulsive leg, and the left leg the landing leg.  The propulsive leg has to produce enough force to project the runner and their legs up and over the hurdle.  This propulsive foot is not in contact with the ground for a very long time, but, the muscles in the right leg must apply a great enough force to the ground to get the runner over the hurdle.  The amount of force applied multiplied by the time interval over which the force is applied is known as impulse.  The primary muscles used during this propulsive phase are the hip extensors (gluteus maximus and hamstrings), the quadriceps, and the gastrocnemius and soleus (calf) muscles.

Once the athlete is in the air, they must now clear the hurdle.  If you look at the athlete's left leg in the picture above, the hip is flexed (moved in front of the torso) while the knee if fully extended (nearly straight).  This places a large amount of tension on the hamstrings; if the athlete does not have good flexibility in this muscle group, they will have difficulty clearing the hurdle and will have a greater risk of injury.  Once the lead leg clears the hurdle, the trail leg also has to clear.  The knee of this leg is in a flexed (bent) position, while the hip is going first extend (go back behind the torso), then abduct (move out to the side), and then flex to clear the hurdle. 

After clearing the hurdle, the athlete is now going to land on the lead or landing leg.  Impulse becomes important again, because the foot/ankle/lower leg has to absorb the impact forces from the ground, which will be applied over a very short time period, and then apply a force to the ground to propel the body forward to continue running.  This running and jumping cycle will be repeated several times (depending on the length of the race) over the course of the event, and one poor jump where the athlete hits the hurdle can take them from 1st place to last place (see the picture below from the men's race).  In order to be successful at this event, the athletes must be able to run at a very high velocity, be able to produce enough force to jump over the hurdle, must have enough flexibility to clear the legs over the hurdle, and must be able to absorb the impact forces when they land.  This is a very demanding event that requires a very specific skill set.