The Hip-twist Jump: A Unique Mechanism for Jumping in Lungless Salamanders
Many terrestrial and aquatic animals jump to escape predators. Most terrestrial animals use robust hindlimbs to produce the power needed to lift their bodies off the ground. This paper explores an alternative jump mechanism used by the lungless salamander, Desmognathus ochrophaeus. Previous work on this jump mechanism suggested that lungless salamanders invoke rapid torso flexion to hurl themselves into the air with minimal hindlimb contribution. The current study was designed to investigate how salamanders pushed off the ground to jump and to determine whether elastic structures contribute to jump power amplification. Specifically, we focused on trunk action, hip rotation, limb placement, and jump power production. We used high speed cameras to film salamander jumps and used these videos to conduct a subsequent motion analysis. Our results demonstrate that prior to jumping, the trunk flexes laterally into a C-shape while the hindlimb (inside of the bend) is planted in front of the hips. Next, the salamander rapidly undulates, rotating the pelvic girdle toward the planted hindfoot. At this point, the planted hindlimb acts like a strut that allows the salamander to pole-vault over the planted hindfoot and into the air. We estimate that the trunk axial muscles are the main contributors to jump power, but they must be aided by elastic structures that amplify jump power output. Future studies should focus on identifying the elastic structures responsible for power amplification as well as possible neurological connections between the salamander jump and the C-start escape strategy of fishes.Abstract
Representative example of the salamander jump from dorsal and lateral views vs. time. Each set of frames indicates a time point along the jump movement. At rest, 0, 25, 50, 75, and 100% of the unloading phase of the jump are represented as A, B, C, D, and E, respectively. At rest, salamanders are in a prone position with a relatively straight trunk (A). During the initial loading phase (B), salamanders bend the trunk into a C-shape and plant the inside hindfoot in front of the hips. At the beginning of the unloading phase (C–D), the trunk reverses direction and lateral undulation rotates the hips, which pivot around the planted takeoff hindlimb, increasing momentum in the horizontal direction. The takeoff hindlimb acts like a strut, redirecting the salamander up and over the hindlimb (D–E). Time is in percent of unloading (jump) phase.
Kinematic analysis of a salamander jumping. Each graph represents kinematic variables (mean ± SEM, n = 5) measured at 0, 25, 50, 75, 100, and 125% of the unloading phase. The point at which the salamander leaves the ground (100%) is indicated by a dotted line in each graph. (A) Location of the torso bend. The lateral undulation during the unloading phase moves the bend posteriorly. The horizontal straight line represents the point at which the apex of the bend is at the center of the hips. (B) Orientation of the hips for a salamander at rest and throughout the jump, in degrees of rotation. Trunk undulation rapidly rotates the hips in a direction away from the inside hindlimb. (C) Center of mass (CoM) movement during the salamander jump. The CoM begins over the planted foot, increasing grip during the early stages of jump. During jump, the CoM shifts away from the foot and into the trunk. (D) A cartoon illustration of salamander jumping with markers emphasizing torso bend (line along torso), hip (straight line across hips), and COM movement (star). The torso bend is produced during the loading phase of the jump (at rest, 0%) and then travels posteriorly during the unloading phase (0–100%) because of salamander undulation. As the C-bend is produced, the hip angle changes to be in line with the planted foot (0%) and then rapidly rotates in the opposite direction for the entire unloading phase (25–100%) and continues into the air (125%). The CoM at rest is within the trunk of the salamander (at rest) and then translates out of the trunk and over the foot during the loading phase (0%). During the unloading phase, the CoM moves back into the trunk (25–100%).
Analysis of foot-ground contact during the unloading phase. (A) Dorsal illustrations of the salamander during each time step of the jump. Shaded limbs indicate that it is in contact with the ground. The takeoff hindfoot remains on the ground until liftoff. (B) Toe-off times (in percent unloading phase) for each limb (mean ± SD). All limbs except the takeoff hindlimb leave the ground at the same time.
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