Physiological cross sectional area .28PCSA.29 Pennate muscle

one advantage of pennate muscles more muscle fibers can packed in parallel, allowing muscle produce more force, although fiber angle direction of action means maximum force in direction less maximum force in fiber direction. muscle cross sectional area (blue line in figure 1, known anatomical cross section area, or acsa) not accurately represent number of muscle fibers in muscle. better estimate provided total area of crossections perpendicular muscle fibers (green lines in figure 1). measure known physiological cross sectional area (pcsa), , commonly calculated , defined following formula (an alternative definition provided in main article):

pcsa

=



muscle volume


fiber length



=



muscle mass


ρ
⋅

fiber length




,


{\displaystyle {\text{pcsa}}={{\text{muscle volume}} \over {\text{fiber length}}}={{\text{muscle mass}} \over {\rho \cdot {\text{fiber length}}}},}

where ρ density of muscle:

ρ
=



muscle mass


muscle volume



.


{\displaystyle \rho ={{\text{muscle mass}} \over {\text{muscle volume}}}.}

pcsa increases pennation angle, , muscle length. in pennate muscle, pcsa larger acsa. in non-pennate muscle, coincides acsa.