Twisting and Bending: The Functional Role of Salamander Lateral Hypaxial Musculature During Locomotion

Abstract

SUMMARY The function of the lateral hypaxial muscles during locomotion in tetrapods is controversial. Currently, there are two hypotheses of lateral hypaxial muscle function. The first, supported by electromyographic (EMG) data from a lizard (Iguana iguana) and a salamander (Dicamptodon ensatus), suggests that hypaxial muscles function to bend the body during swimming and to resist long-axis torsion during walking. The second, supported by EMG data from lizards during relatively high-speed locomotion, suggests that these muscles function primarily to bend the body during locomotion, not to resist torsional forces. To determine whether the results from D. ensatus hold for another salamander, we recorded lateral hypaxial muscle EMGs synchronized with body and limb kinematics in the tiger salamander Ambystoma tigrinum. In agreement with results from aquatic locomotion in D. ensatus, all four layers of lateral hypaxial musculature were found to show synchronous EMG activity during swimming in A. tigrinum. Our findings for terrestrial locomotion also agree with previous results from D. ensatus and support the torsion resistance hypothesis for terrestrial locomotion. We observed asynchronous EMG bursts of relatively high intensity in the lateral and medial pairs of hypaxial muscles during walking in tiger salamanders (we call these ‘α-bursts’). We infer from this pattern that the more lateral two layers of oblique hypaxial musculature, Mm. obliquus externus superficialis (OES) and obliquus externus profundus (OEP), are active on the side towards which the trunk is bending, while the more medial two layers, Mm. obliquus internus (OI) and transversus abdominis (TA), are active on the opposite side. This result is consistent with the hypothesis proposed for D. ensatus that the OES and OEP generate torsional moments to counteract ground reaction forces generated by forelimb support, while the OI and TA generate torsional moments to counteract ground reaction forces from hindlimb support. However, unlike the EMG pattern reported for D. ensatus, a second, lower-intensity burst of EMG activity (‘β-burst’) was sometimes recorded from the lateral hypaxial muscles in A. tigrinum. As seen in other muscle systems, these β-bursts of hypaxial muscle coactivation may function to provide fine motor control during locomotion. The presence of asynchronous, relatively high-intensity α-bursts indicates that the lateral hypaxial muscles generate torsional moments during terrestrial locomotion, but it is possible that the balance of forces from both α- and β-bursts may allow the lateral hypaxial muscles to contribute to lateral bending of the body as well.

Overturning and rolling avoidance by gecko when challenged with inclines

“…more steps are in the supporting phase at the same time, making the body in a state of multiple support (Autumn et al, 2006;Wang et al, 2011), thereby avoiding overturning and rolling on inclined surfaces; (2) flexibility of body and limbs. The elastic deformation of the limbs and body muscles buffers the force and delays the rolling and overturning response (Chen et al, 2006;Bennett et al, 2001), thus achieving stable locomotion. For example, lizards and scorpion muscles can alleviate the impact of force and decrease the effects of unstable impulse moments in motion (Bennett et al, 2001).…”

“…The elastic deformation of the limbs and body muscles buffers the force and delays the rolling and overturning response (Chen et al, 2006;Bennett et al, 2001), thus achieving stable locomotion. For example, lizards and scorpion muscles can alleviate the impact of force and decrease the effects of unstable impulse moments in motion (Bennett et al, 2001). Although the active swing of the tail has always been important to maintain the stability of the locomotion (Jusufi et al, 2008), experimental observations have shown that the gecko does not swing its tail significantly when moving on the inverted slopes, and since the speed of the gecko on the incline is very low (Figure 5A), the inertial force may not be obvious for maintaining stability.…”

The role of load-dependent sensory input in the control of balance during gait in rats

“…Thus, an increased time of the unsupported condition of the ipsilateral forelimbs and hindlimbs, the increased VERT push-off activity, and, possibly, symmetrical activation of the nearest T13 epaxial muscles could be a centrally programmed walk-trot (walksymmetrical running) transition process. The walk gait is consistent with a traveling wave, while synchronized activity of epaxial muscles during trotting is consistent with a standing wave of the trunk bending (O'Reilly et al, 2000;Bennett et al, 2001;Schilling and Carrier, 2010). As a hypothesis, if two patterns of activity of the epaxial muscles from different types of gait (i.e.…”

Modeling and Trajectory Optimization for Standing Long Jumping of a Quadruped with A Preloaded Elastic Prismatic Spine

“…Many existing works abstract the biological evidence of the spine bending [33], [35] during locomotion with one or more revolute joints [23], [25], [30], [47]- [56]. Yet, the resulting considerable change in body length along the sagittal axis also implies the possibility of a prismatic joint interpretation, which has been verified as being effective for facilitating some quadrupedal dynamical gaits [25], [51].…”

“…Existing biological evidence has demonstrated the varied spinal functions of bending and twisting in vertebrate studies [35]. In turn, such studies have motivated several biomimetic multiple-DoF spine models and prototype designs that have been found capable of stabilizing gaits [24], [36]- [42], enhancing speed [40]- [45], and promoting efficiency [40]- [42], [45], [46].…”