title: Indirect evidence for elastic energy playing a role in limb recovery during toad hopping.
abstract: Elastic energy is critical for amplifying muscle power during the propulsive phase of anuran jumping. In this study, we use toads (Bufo marinus) to address whether elastic recoil is also involved after take-off to help flex the limbs before landing. The potential for such spring-like behaviour stems from the unusually flexed configuration of a toad's hindlimbs in a relaxed state. Manual extension of the knee beyond approximately 90° leads to the rapid development of passive tension in the limb as underlying elastic tissues become stretched. We hypothesized that during take-off, the knee regularly extends beyond this, allowing passive recoil to help drive limb flexion in mid-air. To test this, we used high-speed video and electromyography to record hindlimb kinematics and electrical activity in a hindlimb extensor (semimembranosus) and flexor (iliofibularis). We predicted that hops in which the knees extended further during take-off would require less knee flexor recruitment during recovery. Knees extended beyond 90° in over 80% of hops, and longer hops involved greater degrees of knee extension during take-off and more intense semimembranosus activity. However, knee flexion velocities during recovery were maintained despite a significant decrease in iliofibularis intensity in longer hops, results consistent with elastic recoil playing a role.
authors.affiliation: Department of Biology, Mount Holyoke College, South Hadley, MA 01075, USA.
authors.forename: Ariela
authors.initials: A
authors.lastname: Schnyer
authors.affiliation: Department of Biology, Mount Holyoke College, South Hadley, MA 01075, USA.
authors.forename: Mirialys
authors.initials: M
authors.lastname: Gallardo
authors.affiliation: Program in Organismic and Evolutionary Biology, University of Massachusetts, Amherst, MA 01003, USA.
authors.forename: Suzanne
authors.initials: S
authors.lastname: Cox
authors.affiliation: Department of Biology, Mount Holyoke College, South Hadley, MA 01075, USA Program in Organismic and Evolutionary Biology, University of Massachusetts, Amherst, MA 01003, USA ggillis@mtholyoke.edu.
authors.forename: Gary
authors.initials: G
authors.lastname: Gillis
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002024:Bufo marinus / Q000502:physiology*; D004548:Elasticity; D004576:Electromyography; D006614:Hindlimb / Q000502:physiology; D008124:Locomotion / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D014741:Video Recording
keywords: elastic energy; electromyography; jumping; kinematics; muscle; toads