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      Standing horse posture: a longer stance is more stable

      research-article
      1 , * , 2
      Biology Open
      The Company of Biologists Ltd
      Horse, Posture, Balance, Equilibrium, Stability, Mechanism

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          ABSTRACT

          Horses stand for most of each day. Although they can use various leg configurations (postures), they usually stand with vertical legs. Why? We addressed this question with a 2D quasi-static model having three rigid parts: a trunk, massless fore-limbs and massless rear limbs, with hinges at the shoulders, hips, and hooves. The postural parameter we varied was ℓ g, the distance between the hooves. For a given ℓ g, statics finds an equilibrium configuration which, with no muscle stabilization (i.e. using minimal effort) is unstable. We assume a horse uses that configuration. To measure the neuromuscular effort needed to stabilize this equilibrium, we added springs at the shoulder and hip; the larger the springs needed to stabilize the model ( k min), the more neuromuscular effort needed to stabilize the posture. A canted-in posture (small ℓ g), observed habitually in some domestic horses, needs about twice the spring stiffness (representing twice the effort) as is needed with vertical or slightly splayed-out (large ℓ g) legs. This relationship of posture and stability might explain the prevalence of vertical or slightly splayed-out legs in wild and healthy domestic horses and leaves as a puzzle why some horses stand canted-in.

          Abstract

          Summary: Without stabilizing muscles, a standing horse is unstable. The bigger the spacing between fore and hind hooves, the less muscular effort needed for stabilization.

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          Most cited references37

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          Passive Dynamic Walking

          T McGeer (1990)
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            Energetics of running: a new perspective.

            The amount of energy used to run a mile is nearly the same whether it is run at top speed or at a leisurely pace (although it is used more rapidly at the higher speed). This puzzling independence of energy cost and speed is found generally among running animals, although, on a per gram basis, cost is much higher for smaller animals. Running involves little work against the environment; work is done by muscles and tendons to lift and accelerate the body and limbs. Some of the work is recovered from muscle-tendon springs without metabolic cost and work rate does not parallel metabolic rate with either speed or size. Regardless of the amount of work muscles do, they must be activated and develop force to support the weight of the body. Load-carrying experiments have shown that the cost of supporting an extra newton of load is the same as the weight-specific cost of running. Size differences in cost are proportional to stride frequency at equivalent speeds, suggesting that the time available for developing force is important in determining cost. We report a simple inverse relationship between the rate of energy used for running and the time the foot applies force to the ground during each stride. These results support the hypothesis that it is primarily the cost of supporting the animal's weight and the time course of generating this force that determines the cost of running.
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              Bipedal locomotion: effects of speed, size and limb posture in birds and humans

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                Author and article information

                Journal
                Biol Open
                Biol Open
                BIO
                biolopen
                Biology Open
                The Company of Biologists Ltd
                2046-6390
                15 April 2022
                12 May 2022
                12 May 2022
                : 11
                : 4
                Affiliations
                [1 ]Maximum Horsepower Research , Ithaca, NY, USA
                [2 ]Mechanical Engineering, Cornell University , Ithaca, NY 14853, USA
                Author notes
                [* ]Author for correspondence ( equinesportsmed@ 123456mac.com )
                Article
                BIO059139
                10.1242/bio.059139
                9115912
                35545924
                6c56896c-336b-45f0-9759-2ea744f5a3bd
                © 2022. Published by The Company of Biologists Ltd

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.

                Product
                Funding
                Funded by: American Holistic Veterinary Medical Foundation, 26-1583307;
                Categories
                Research Article

                Life sciences
                horse,posture,balance,equilibrium,stability,mechanism
                Life sciences
                horse, posture, balance, equilibrium, stability, mechanism

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