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Functional capacity of kangaroo rat hindlimbs: adaptations for locomotor performance.

Authors
  • Rankin, Jeffery W1, 2
  • Doney, Kelsey M3
  • McGowan, Craig P4, 5
  • 1 Department of Biological Sciences, The University of Idaho, Moscow, ID, USA.
  • 2 Pathokinesiology Laboratory, Rancho Los Amigos National Rehabilitation Center, Downey, CA, USA.
  • 3 Department of Physical Therapy, Simmons College, Boston, MA, USA.
  • 4 Department of Biological Sciences, The University of Idaho, Moscow, ID, USA [email protected]
  • 5 WWAMI Medical Education Program, The University of Idaho, Moscow, ID, USA.
Type
Published Article
Journal
Journal of The Royal Society Interface
Publisher
The Royal Society
Publication Date
Jul 01, 2018
Volume
15
Issue
144
Identifiers
DOI: 10.1098/rsif.2018.0303
PMID: 29997260
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Many cursorial and large hopping species are extremely efficient locomotors with various morphological adaptations believed to reduce mechanical demand and improve movement efficiency, including elongated distal limb segments. However, despite having elongated limbs, small hoppers such as desert kangaroo rats (Dipodomys deserti) are less efficient locomotors than their larger counterparts, which may be in part due to avoiding predators through explosive jumping movements. Despite potentially conflicting mechanical demands between the two movements, kangaroo rats are both excellent jumpers and attain high hopping speeds, likely due to a specialized hindlimb musculoskeletal morphology. This study combined experimental dissection data with a static analysis of muscle moment generating capacities using a newly developed musculoskeletal model to characterize kangaroo rat hindlimb musculoskeletal architecture and investigate how morphology has evolved to meet hopping and jumping mechanical demands. Hindlimb morphology appears biased towards generating constant moment arms over large joint ranges of motion in this species, which may balance competing requirements by reducing the need for posture and movement specific excitation patterns. The ankle extensors are a major exception to the strong positive relationship exhibited by most muscles between muscle architecture parameters (e.g. Lfibre) and joint moment arms. These muscles appear suited to meeting the high moments required for jumping: the biarticular nature of the ankle extensors is leveraged to reduce MTU strain and create a four-bar linkage that facilitates proximal force transfer. The kangaroo rat hindlimb provides an interesting case study for understanding how morphology balances the sometimes competing demands of hopping and jumping. © 2018 The Author(s).

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