New research illustrates that birds use a hybrid gait at intermediate speeds
20 May 2010
Research at the Royal Veterinary College (RVC) has discovered that birds use a third ‘hybrid’ gait at intermediate speeds, going against the mechanics of walking and running understood by many.
Humans walk with relatively stiff limbs, ‘vaulting’ over a leg each step and run with more compliant legs with a flight phase between each stance. However, these new findings indicate that there is a gait totally unfamiliar to normal humans, which involves achieving both walking-like vaulting and running-like ballistic mechanics during the hybrid gait.
The RVC’s Structure and Motion Laboratory team discovered that guinea fowl and pheasants never quite take off during the ballistic phase. Researcher Dr. Jim Usherwood refers to this hybrid gait as ‘Grounded Inverted Pendular Running’ or the GIPR gait, for short.
 RVC research has discovered that birds use a 'hybrid' gait at intermediate speeds |
 The hybrid gait supports the notion that many aspects of gait mechanics can be understood without requiring detailed musculoskeletal models or a presumption of spring-like leg properties |
“The ‘GIPR’ involves both relatively stiff-limbed walking-like vaulting over midstance, and near-ballistic running-like phases between stances,” explains Usherwood. “This discovery supports the previous idealised models of walking and running which demonstrate that, energetically, walking should be favoured up to, and even somewhat over, those speeds and step lengths that can be achieved while retaining the stance leg under compression.”
Recently, numerical energetic optimisations of reductionist models have considered a huge range of potential bipedal gaits, and demonstrated that walking and running, and this third, strange, hybrid gait should be favoured at certain speeds and step lengths.
To test these predictions, the centre-of-mass velocities of four guinea fowl and three pheasants (during locomotion and at a range of speeds) were calculated from integrating acceleration data derived from force plate measurements by the RVC.
“This new gait supports the notion that many aspects of gait mechanics can be understood without the need for detailed musculoskeletal models or a presumption of spring-like leg properties. It also raises the possibility that hybrid or unconventional gaits might be valuable in improving the efficiency of bipedal robots,” concludes Usherwood.
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