Brief Communications

Nature 421, 35-36 (2 January 2003) | doi:10.1038/421035a

Biomechanics: A catapult action for rapid limb protraction

Alan M. Wilson1,2, Johanna C. Watson1 & Glen A. Lichtwark2

Fast runners must be able to protract their limbs quickly in order to prepare for the next stance phase1, 2, 3. This is particularly challenging for large animals as their limbs are long4 and their muscles contract slowly and have a low power output5, 6. Here we show that horses cannot achieve the high power output required for rapid limb protraction by simple muscle contraction and that they instead deploy an elastic biceps muscle to store and then release bursts of energy — this muscle's catapult action has an output that is comparable to over 100 times its mass of non-elastic muscle. Although grasshoppers and fleas are known to rely on a similar catapult mechanism for rapid acceleration7, 8, to our knowledge this has not been demonstrated before in larger animals.

  1. Structure and Motion Laboratory, Department of Veterinary Basic Sciences, The Royal Veterinary College, Hatfield, Herts AL9 7TA, UK
  2. Institute of Human Performance, University College London, Stanmore, Middlesex HA7 4LP, UK

Correspondence to: Alan M. Wilson1,2 e-mail: Email: