Accessible Summary:

Purpose: Two receptors are available to respond to vertical deformations and shear stress on the plantar surface: SA II mechanoreceptors and nociceptors with c-fibre afferents.  The nociceptors have high thresholds and are thought to respond to impending tissue damage.  To clarify which receptor is mainly used to eliciting behavior that alters locomotion we compared the relation between painful stimuli and signs of tissue damage on hairy skin and plantar skin.

Synopsis: Intense plantar surface (glabrous skin) horizontal and vertical loading was applied so as to reach pain threshold.  The volley of 35 painful sequential plantar loads produced no visible signs of plantar surface damage whereas signs of damage was found on hairy skin similarly loaded.  This indicates that pain threshold to plantar loading is set extremely low, and does not signal impending damage.  This suggests that the SA II mechanoreceptors usually guide human locomotion.

Significance: This reports further advances the notion that plantar  pain from localized plantar mechanical stimulation does not signal impending damage - rather it is used for another purpose such as guiding human locomotion.  In addition, differences in pain threshold across the plantar surface directs loads from easily damaged structures. Marti's report which found a strong positive relation between injury frequency and shoe cost was first mentioned in this report.