Different Physiologic Cross-sectional Areas

Suppose that two muscles had identical fiber lengths and pennation angles, but one muscle had twice the mass (equivalent to saying that one muscle had twice the number of fibers and thus twice the PCSA). What would be the difference in their mechanical properties? How would the length-tension and force-velocity curves be affected?

Effect of PCSA on Force Production

This schematic demonstrates that the only effect is to increase maximum tetanic tension so that the length-tension curve has the same basic shape but is simply amplified upward in the case of the stronger muscle. Similarly, the force-velocity curve simply changes the location of Po, but the curve retains the same basic shape. Note that if both curves are plotted on relative scales (i.e., percent maximum tension instead of absolute tension), the two muscles of different architecture appear to have identical properties. This demonstrates that while architectural properties profoundly affect the extrinsic muscle properties (i.e., the properties that vary with absolute muscle size, such as PCSA or mass), they have no affect on its intrinsic properties (i.e., the properties that are independent of absolute muscle size, such as fiber length/muscle length ratio).