Pennation Angle, Physiological Cross Sectional Area (PCSA), & Sprinting
Muscles attach to bones through the tendon. In a lot of muscles the end of the muscle fibers are arranged at an acute angle to the tendon which is called pennation, specific to the structure of the muscle
The PSCA of the muscle is the area of the cross-section of the muscle oriented perpendicular to the fibers. Hypertrophy training builds more PSCA and changes the pennation angle to make it more obtuse or a larger angle. The more PSCA allows the muscle to generate more force.
In sports performance, this can be good and bad because:
Muscle shortening velocity = cosine of the pennation angle
Without getting into the math— the higher the pennation angle = the slower the muscle shortening velocity
Lower pennation angle = faster muscle shortening velo
Now what does this mean for sprinting and sports performance?
Let’s look at Kumagai et al (2000)
The faster sprinter had significantly lower pennation angles and longer fascicle lengths in the quad and calf muscle. Makes sense because this means a faster contraction velocity. However, they also showed that the faster sprinters also had greater muscle thickness in the UPPER quad & calf and then the muscle thickness is lowered around the joint to decrease pennation angle and improve contraction velocity. This is important because a lower pennation angle also means a greater percentage of force transferred to the tendon to allow it to do its job of storing and releasing elastic energy.
To bring this all together:
The faster sprinter has great thickness in the upper quad and calf to generate force and then the thickness is lessened around the joint to lower pennation, increase contraction velocity, & transfer that force from the upper quad to the tendons
Elite sprinter like Ben Johnson are built to maximize this biomechanical concept to generate a great amount of force at the fastest rate possible
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