Horses damp the spring in their step

Nature. 2001 Dec 20-27;414(6866):895-9. doi: 10.1038/414895a.

Abstract

The muscular work of galloping in horses is halved by storing and returning elastic strain energy in spring-like muscle-tendon units.These make the legs act like a child's pogo stick that is tuned to stretch and recoil at 2.5 strides per second. This mechanism is optimized by unique musculoskeletal adaptations: the digital flexor muscles have extremely short fibres and significant passive properties, whereas the tendons are very long and span several joints. Length change occurs by a stretching of the spring-like digital flexor tendons rather than through energetically expensive length changes in the muscle. Despite being apparently redundant for such a mechanism, the muscle fibres in the digital flexors are well developed. Here we show that the mechanical arrangement of the elastic leg permits it to vibrate at a higher frequency of 30-40 Hz that could cause fatigue damage to tendon and bone. Furthermore, we show that the digital flexor muscles have minimal ability to contribute to or regulate significantly the 2.5-Hz cycle of movement, but are ideally arranged to damp these high-frequency oscillations in the limb.

MeSH terms

  • Animals
  • Biomechanical Phenomena
  • Elasticity
  • Forelimb
  • Gait
  • Horses / anatomy & histology
  • Horses / physiology*
  • Leg Bones / physiology*
  • Locomotion
  • Models, Biological
  • Muscle Fibers, Skeletal / physiology
  • Muscle, Skeletal / anatomy & histology
  • Muscle, Skeletal / physiology*
  • Tendons / anatomy & histology
  • Tendons / physiology*
  • Vibration