Which Factors Contribute to Force Production? (Part 2)

2. Morphological factors

2.1 Muscle Fiber Type

fiber type

There are differences in muscle fiber distribution, both intra and inter individual. Different athletes show different % of slow vs fast fibers. Additionally, different muscles within the same athlete have different fiber type distribution. Even further, within a muscle there are different fiber types. This distribution is dependent both on genetic factors and training history.

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Depending on the fiber type dominance, force production potential can be affected.

2.2 Muscle Architecture

architecture.jpg

2,2,1 Cross – Sectional Area

cross sectional area

—Physiological CSA  —Anatomical CSA

Generally, the greater the PCSA the greater the force production potential. In other words, if a muscle has more sarcomeres in parallel. it has the ability to produce more force. That can be achieved both through an increase of number of sarcomeres and/or an increase in pennation angle, as we will see next.

2.2.2 Pennation Angle

800px-Pennation_angle_of_fibers_in_pennate_muscle.png

An increase in pennation angle is associated with greater potential to produce force. This is due to an increase in sarcomeres in parallel, increasing therefore PSCA, resulting in greater ability to produce force. An increase in pennation angle in a typical adaptation after training with heavy loads. On the other hand, a decrease in pennation angle is associated with greater potential to higher contraction velocities, and as we saw before this reduces the potential to produce force. This is due to more sarcomeres in series and greater fascicle length, as we will see next.

2.2.3 Fascicle Length

fig-1-full.png

An increase in fascicle length is a result of more sacromeres in series (longitudinal). Since a decrease in pennation angle results in a decrease of PSCA, it is associated with reduced force production potential. However, it allows for greater contraction velocities, which is a common adaptation after ballistic and speed training.

2.3 Tendon Properties

F2.large.jpg

Tendon or muscel tendon unit (MTU) has two distinct properties: stiffness and compliance. Particularly, tendon stiffness has important implications for performance since it allows for a more efficient storage and utilization of elastic energy, which drives greater force production as we saw before.

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