Relationship between PCSA and muscle force Pennate muscle

the total force exerted fibers along oblique direction proportional pcsa. if specific tension of muscle fibers known (force exerted fibers per unit of pcsa), can computed follows:

total force

=

pcsa

⋅

specific tension



{\displaystyle {\text{total force}}={\text{pcsa}}\cdot {\text{specific tension}}}

however, component of force can used pull tendon in desired direction. component, true muscle force (also called tendon force), exerted along direction of action of muscle:

muscle force

=

total force

⋅
cos
⁡
Φ


{\displaystyle {\text{muscle force}}={\text{total force}}\cdot \cos \phi }

the other component, orthogonal direction of action of muscle (orthogonal force = total force × sinΦ) not exerted on tendon, squeezes muscle, pulling aponeuroses toward each other.

notice that, although practically convenient compute pcsa based on volume or mass , fiber length, pcsa (and therefore total fiber force, proportional pcsa) not proportional muscle mass or fiber length alone. namely, maximum (tetanic) force of muscle fiber depends on thickness (cross-section area) , type. no means depends on mass or length alone. instance, when muscle mass increases due physical development during childhood, may due increase in length of muscle fibers, no change in fiber thickness (pcsa) or fiber type. in case, increase in mass not produce increase in force.