Different Fiber Lengths

Let us consider the effects of architecture using an example of two muscles with identical PCSAs and pennation angles but different fiber lengths. Before reading ahead, try to draw the appropriate length-tension and force-velocity curves.

As shown below, the effect is to increase the muscle velocity (or, stated identically, to increase the muscle excursion). The peak absolute force of the length-tension curves is identical, but the absolute muscle active range is different. That sounds a lot like active range of motion (ROM), a measurement that is extremely important in clinical evaluation. In fact, it is directly related to ROM--ROM is a direct result of muscle architecture and the joint properties on which the muscle acts.

For the same reason that fiber length increases the active muscle range of the length-tension relationship, it causes an increase in the muscle's absolute maximum contraction velocity (Vmax). Again, while the fiber length increase causes an increase in these extrinsic properties, it has no effect on the intrinsic properties of the muscle. A similar exercise can be performed comparing muscles with different PCSAs and fiber lengths. Try predicting force-velocity and length-tension curves for the case where both architectural parameters are changed.

Force-Length diagram