Knee/leg stiffness
Visit a local track club session or 10k start line and observe the wide varieties of running technique on display. In the attempt to put one foot in front of the other, somehow, we all do it differently. When we try to run as fast, the reasons person A runs faster than person B shines out. Remember if you’re trying 100% you are trying/running/racing as hard as Mo Farah. Usually just a whole lot slower and with a totally different technique!
So, what varies between the different times achieved, let say, of a half marathon?
We all line up at the start and take our first 6 steps, which in fact are the best steps you take in the whole race, full of glucose and power. The two big variables are leg stiffness and foot contact.
Leg stiffness/vertical spring
This is the ability to strike the floor with a straighter (not locked) knee and it not compress on contact (pic 1). The better you are at this the better you are at part 2, the foot contact. Stiffness reduces the load on the quadriceps (front of the thigh), load on the soleus (one of the muscles that make up the calf muscles), places it into the achilles tendon (that’s a great thing) and distributes the impact across both calf muscles. The achilles is a provider of energy preserving power through a system called the stretch shortening cycle (SSC). The SSC basically means for each stride you use less energy, have more bounce (resulting in both feet off the floor) and travel a greater at speed. The floor impact is also shared between the two calf muscles called the gastrocnemius and soleus resulting in less chance of cramp from localised fatigue in the one muscle (cramp is a sign of overuse) and achilles soreness.