Mechanics of torque generation during quadrupedal arboreal locomotion

SUMMARYArboreal substrates differ not only in diameter, but also in continuity and orientation. To gain more insight into the dynamics of small-branch locomotion in tetrapods we studied the veiled chameleon walking on inclined and declined perches of up to 60deg slope. We found that forelimbs and hindlimbs contribute equally to the bodyʼs progression along inclines and declines. The higher-positioned limbʼs vertical impulses decreased with slope. And although vertical impulses in the lower-positioned limb increased with substrate slope, peak vertical forces decreased. The decrease in peak vertical forces in the lower-positioned limb can be explained by a considerable increase of tensile forces in the higher-positioned limb as the slope increases. In addition, limbs were more crouched on slopes whereas no changes in forward and backward reach were observed. Mediolateral impulses were the smallest amongst the force components, and lateral impulses (medially directed limb forces) exceeded medial impulses (laterally directed limb forces). On inclines and declines, limb placement was more variable than on level substrates. The tail never contacted the substrate during level locomotion; however, on inclines and declines, the tail was held closer to the substrate, with short substrate contacts in one-third of the analyzed trials. Regardless of substrate orientation the tail was always held straight above the branch; therefore, rotational moments induced by the tail were minimized. Supplementary material available online at

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Biodynamics of climbing: effects of substrate orientation on the locomotion of a highly arboreal lizard (Chamaeleo calyptratus)

Krause

Fischer

2012

“…Thus, the relative propulsive contribution of the forelimb is dependent, at least partially, on the orientation of the animal, likely increasing in importance with increasing slope. Perches of narrow diameter increase the likelihood of toppling because the sloped sides and the narrow base of support increase the proportion of the gravitational force acting tangentially to the perch, creating a toppling moment that increases with deflection of the CoM away from the perch (Preuschoft, 2002;Lammers and Biknevicius, 2004;Lammers and Gauntner, 2008). Although claws and adhesive structures of lizards help grip and maintain contact with the surface in the face of these challenges (Zani, 2000), both sets of limbs must undergo changes in posture and function to contribute to overcoming the greater challenges for propulsion and stability.…”

Section: Changes With Incline and Perch Diametermentioning

confidence: 99%

How forelimb and hindlimb function changes with incline and perch diameter in the green anole,Anolis carolinensis

Foster

Higham

2012

SUMMARYThe range of inclines and perch diameters in arboreal habitats poses a number of functional challenges for locomotion. To effectively overcome these challenges, arboreal lizards execute complex locomotor behaviors involving both the forelimbs and the hindlimbs. However, few studies have examined the role of forelimbs in lizard locomotion. To characterize how the forelimbs and hindlimbs differentially respond to changes in substrate diameter and incline, we obtained three-dimensional high-speed video of green anoles (Anolis carolinensis) running on flat (9cm wide) and narrow (1.3cm) perches inclined at 0, 45 and 90deg. Changes in perch diameter had a greater effect on kinematics than changes in incline, and proximal limb variables were primarily responsible for these kinematic changes. In addition, a number of joint angles exhibited greater excursions on the 45deg incline compared with the other inclines. Anolis carolinensis adopted strategies to maintain stability similar to those of other arboreal vertebrates, increasing limb flexion, stride frequency and duty factor. However, the humerus and femur exhibited several opposite kinematic trends with changes in perch diameter. Further, the humerus exhibited a greater range of motion than the femur. A combination of anatomy and behavior resulted in differential kinematics between the forelimb and the hindlimb, and also a potential shift in the propulsive mechanism with changes in external demand. This suggests that a better understanding of single limb function comes from an assessment of both forelimbs and hindlimbs. Characterizing forelimb and hindlimb movements may reveal interesting functional differences between Anolis ecomorphs. Investigations into the physiological mechanisms underlying the functional differences between the forelimb and the hindlimb are needed to fully understand how arboreal animals move in complex habitats.

“…This study contributes new data to a growing body of comparative literature addressing kinematic responses of (adult) small-bodied mammals to arboreal substrates, including those that are arboreally adapted with grasping extremities (Pridmore, 1994;Schmitt, 2003b;Schmitt and Lemelin, 2004;Delciellos and Vieira, 2006;Stevens, 2006;Delciellos and Vieira, 2007;Scheibe et al, 2007;Stevens, 2007;Nyakatura et al, 2008;Nyakatura and Heymann, 2010) and those that lack grasping capability and are predominantly terrestrial (Lemelin et al, 2003;Lammers and Biknevicius, 2004;Lammers, 2007;Lammers and Gauntner, 2008;Lammers, 2009;Schmidt and Fischer, 2010;Lammers and Zurcher, 2011). Much insight on L. J. Shapiro and J. W. Young arboreal adaptations has been gained from these studies, but this study is one of very few to provide ontogenetic kinematic data for mammals in an arboreal context (e.g.…”

Section: Discussionmentioning

confidence: 93%

“…From a functional perspective, increasing limb phase within LSDC gait when switching from a flat board to a pole moves the limb sequencing closer to a pure 'trot'. In a trot, contralateral limbs grasp the surface simultaneously (or near simultaneously), theoretically permitting the production of balanced torques to counter potential rolling moments (Prost, 1969;Preuschoft, 2002;Lammers and Gauntner, 2008;Young and Demes, 2010). Although limb phase itself was not influenced by the relative diameter of the poles, sugar gliders, regardless of age, used limb phase/duty factor combinations that enhanced their stability in the face of decreasing relative pole diameter by increasing the number of supporting limbs used throughout the stride.…”

Section: Locomotor Ontogeny In Sugar Glidersmentioning

confidence: 99%

Kinematics of quadrupedal locomotion in sugar gliders (Petaurus breviceps): effects of age and substrate size

Shapiro

Young

2012

SUMMARY Arboreal mammals face unique challenges to locomotor stability. This is particularly true with respect to juveniles, who must navigate substrates similar to those traversed by adults, despite a reduced body size and neuromuscular immaturity. Kinematic differences exhibited by juveniles and adults on a given arboreal substrate could therefore be due to differences in body size relative to substrate size, to differences in neuromuscular development, or to both. We tested the effects of relative body size and age on quadrupedal kinematics in a small arboreal marsupial (the sugar glider, Petaurus breviceps; body mass range of our sample 33-97 g). Juvenile and adult P. breviceps were filmed moving across a flat board and three poles 2.5, 1.0 and 0.5 cm in diameter. Sugar gliders (regardless of age or relative speed) responded to relative decreases in substrate diameter with kinematic adjustments that promote stability; they increased duty factor, increased the average number of supporting limbs during a stride, increased relative stride length and decreased relative stride frequency. Limb phase increased when moving from the flat board to the poles, but not among poles. Compared with adults, juveniles (regardless of relative body size or speed) used lower limb phases, more pronounced limb flexion, and enhanced stability with higher duty factors and a higher average number of supporting limbs during a stride. We conclude that although substrate variation in an arboreal environment presents similar challenges to all individuals, regardless of age or absolute body size, neuromuscular immaturity confers unique problems to growing animals, requiring kinematic compensation.