Quadruped Locomotion Notes

“Exploring Biomechanics: Animals in Motion” by R. McNeill Alexander

Most quadrupedal mammals of the size of cats or larger switch back and forth between three different gaits: the walk, the trot, and the gallop (although smaller animals like mice seldom walk).

  • Walk
    • Each foot is on the ground more than half the time.
    • Four feet are set down in turn, generally at roughly equal intervals of time and almost always in this order:
      • left fore
      • right hind
      • right fore
      • left hind
      • left fore
      • etc
    • The legs are not kept as straight as in human walking, and the pendulum effect is less pronounced.
  • Trotting/Galloping
    • Each foot is on the ground for less than half the stride.
    • Possible stage in the stride where all four feet are off the ground, but at least there are stages when both fore feet, or both hind feet, are off.
    • Trotting: feet move in diagonally opposite pairs.
      • Left fore with the right hind
      • Right fore with the left hind
  • In walking and trotting, the left and right feet of a pair are set down at equal intervals;
    • for example, if the right fore foot is set down a quarter of a second after the left, the left is set down a quarter of a second after the right.
  • In a gallop, the intervals are unequal.
    • The two feet of a pair are set down in rapid succession, and then a longer interval follows before the first is set down again.
    • The two hind feet are set down and then the two fore.
  • The canter, sometimes recognized as a distinct gait, is a slow gallop in which the first fore foot is set down at the same time as the second hind.
  • The footfall pattern of galloping makes it possible for the animals to lengthen the stride by bending and extending the back.
    • While only the fore feet are on the ground, the back bends, pulling the hindquarters forward.
    • While only the hind feet are on the ground, the back straightens again, pushing the forequarters forward.
  • The principal muscle that straightens the back is connected to the skeleton of the hindquarters by a sheet of tendon (aponeurosis)
    • Elastic properties that allow it to be used as an energy saving spring (only in galloping).
    • Kinetic energy is associated with this movement whenever the legs are moving relative to the body’s center of gravity.
      • At the end of its forward swing and again at the end of its backward one, each leg has to stop and start swinging the opposite way: it has to lose and regain kinetic energy twice in each stride.
      • Faster the run, the faster the legs have to swing and the larger the swings in the kinetic energy.
  • Speeds (Study from Dan Hoyt and Richard Taylor of Harvard University. Mentioned in book, p. 35)
    • Walking: 0-1.75m/s (most efficient between 1-1.5m/s)
    • Trotting: 1.0 m/s – 5.0 m/s (most efficient between 2.8m/s – 3.8m/s)
    • Galloping: 3.4 m/s – 6/75 m/s (most efficient between 5.0m/s – 5.75m/s)
  • Horses usually select the most economic gait, walking below 1.5m/s, trotting at 2.8-3.8, and galloping above 5m/s. The ponies usually avoided speeds near the intersections (graph) in the graph: They accelerated quickly from walking well below 1.7 m/s to trotting well above it, and from trotting well below 4.6 m/s to galloping well above it.
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