title: In search of the pitching momentum that enables some lizards to sustain bipedal running at constant speeds.
abstract: The forelimbs of lizards are often lifted from the ground when they start sprinting. Previous research pointed out that this is a consequence of the propulsive forces from the hindlimbs. However, despite forward acceleration being hypothesized as necessary to lift the head, trunk and forelimbs, some species of agamids, teiids and basilisks sustain running in a bipedal posture at a constant speed for a relatively long time. Biomechanical modelling of steady bipedal running in the agamid Ctenophorus cristatus now shows that a combination of three mechanisms must be present to generate the angular impulse needed to cancel or oppose the effect of gravity. First, the trunk must be lifted significantly to displace the centre of mass more towards the hip joint. Second, the nose-up pitching moment resulting from aerodynamic forces exerted at the lizard's surface must be taken into account. Third, the vertical ground-reaction forces at the hindlimb must show a certain degree of temporal asymmetry with higher forces closer to the instant of initial foot contact. Such asymmetrical vertical ground-reaction force profiles, which differ from the classical spring-mass model of bipedal running, seem inherent to the windmilling, splayed-legged running style of lizards.
authors: Evolutionary Morphology of Vertebrates, Ghent University, Gent, Belgium. sam.vanwassenbergh@ugent.be
authors: Sam
authors: S
authors: Van Wassenbergh
authors: Peter
authors: P
authors: Aerts
mesh_terms: D000054:Acceleration; D000818:Animals; D001696:Biomechanical Phenomena; D005552:Forelimb / Q000502:physiology*; D005684:Gait / Q000502:physiology*; D057446:Hydrodynamics; D008116:Lizards / Q000502:physiology*; D008954:Models, Biological; D012420:Running / Q000502:physiology*; D013045:Species Specificity
keywords: aerodynamics; agamids; biomechanics; locomotion; sprinting
references: J Exp Biol. 1999 May;202 (Pt 9):1047-65
references: 10101105
references: Proc Natl Acad Sci U S A. 2004 Nov 30;101(48):16784-8
references: 15550546
references: Am J Physiol. 1977 Nov;233(5):R243-61
references: 411381
references: Proc Biol Sci. 2006 Nov 22;273(1603):2861-7
references: 17015312
references: Science. 2009 Jul 17;325(5938):314-8
references: 19608917
references: J Exp Biol. 2008 Jul;211(Pt 13):2058-65
references: 18552294
references: J Exp Biol. 2012 Jan 15;215(Pt 2):247-55
references: 22189768
references: J Exp Biol. 2011 Aug 1;214(Pt 15):2616-30
references: 21753056
references: J Exp Biol. 2011 Feb 15;214(Pt 4):657-64
references: 21270315
references: J Exp Biol. 2012 Sep 15;215(Pt 18):3293-308
references: 22693026
references: Braz J Biol. 2008 Aug;68(3):649-55
references: 18833488
references: Philos Trans R Soc Lond B Biol Sci. 2003 Sep 29;358(1437):1525-33
references: 14561343
references: Nat Commun. 2010 Sep 07;1:70
references: 20842191
references: Physiol Rev. 1989 Oct;69(4):1199-227
references: 2678167
references: J Exp Biol. 2003 Dec;206(Pt 23):4363-77
references: 14581605