A new look at the Dynamic Similarity Hypothesis: The importance of swing phase

David A. Raichlen, Herman Pontzer, Liza J. Shapiro

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


The Dynamic Similarity Hypothesis (DSH) suggests that when animals of different size walk at similar Froude numbers (equal ratios of inertial and gravitational forces) they will use similar size-corrected gaits. This application of similarity theory to animal biomechanics has contributed to fundamental insights in the mechanics and evolution of a diverse set of locomotor systems. However, despite its popularity, manymammals fail to walk with dynamically similar stride lengths, a key element of gait that determines spontaneous speed and energy costs. Here, we show that the applicability of the DSH is dependent on the inertial forces examined. In general, the inertial forces are thought to be the centripetal force of the inverted pendulum model of stance phase, determined by the length of the limb. If instead we model inertial forces as the centripetal force of the limb acting as a suspended pendulum during swing phase (determined by limb center of mass position), the DSH for stride length variation is fully supported. Thus, the DSH shows that inter-specific differences in spatial kinematics are tied to the evolution of limb mass distribution patterns. Selection may act on morphology to produce a given stride length, or alternatively, stride length may be a "spandrel" of selection acting on limb mass distribution.

Original languageEnglish (US)
Pages (from-to)1032-1036
Number of pages5
JournalBiology Open
Issue number10
StatePublished - Oct 15 2013
Externally publishedYes


  • Biomechanics
  • Froude
  • Locomotion
  • Primate
  • Quadrupedalism
  • Spandrels

ASJC Scopus subject areas

  • General Biochemistry, Genetics and Molecular Biology
  • General Agricultural and Biological Sciences


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