Can we just forget about pennation angle?

Abstract

Skeletal muscle design studies, based on anatomical structure, extend back several hundred years. Accurate anatomical drawings show that many muscle fibers are oriented at an angle relative to a muscle's axis of force generation. This pennation angle has been reported in the skeletal muscle biomechanics literature, primarily in the context of trying to understand muscle force generation. In this perspective, I will describe several discoveries that changed my understanding of pennation and I will suggest that muscle pennation has little if any functional significance. I believe that the correct view of pennation is that it represents a packing strategy whereby short fibers can be packed into a limited volume. While surface pennation angle is easily measured, is very descriptive, and changes during force generation, I believe it has no functional significance.