The association between muscle architecture and muscle spindle abundance

Across the human body, skeletal muscles have a broad range of biomechanical roles that employ complex proprioceptive control strategies to successfully execute a desired movement. This information is derived from peripherally located sensory apparatus, the muscle spindle and Golgi tendon organs. The abundance of these sensory organs, particularly muscle spindles, is known to differ considerably across individual muscles. Here we present a comprehensive data set of 119 muscles across the human body including architectural properties (muscle fibre length, mass, pennation angle and physiological cross-sectional area) and statistically test their relationships with absolute spindle number and relative spindle abundance (the residual value of the linear regression of the log-transformed spindle number and muscle mass). These data highlight a significant positive relationship between muscle spindle number and fibre length, emphasising the importance of fibre length as an input into the central nervous system. However, there appears to be no relationship between muscles architecturally optimised to function as displacement specialists and their provision of muscle spindles. Additionally, while there appears to be regional differences in muscle spindle abundance, independent of muscle mass and fibre length, our data provide no support for the hypothesis that muscle spindle abundance is related to anatomical specialisation.