Lines of non-extension

In the field of biomechanics, the lines of non-extension are notional lines running across the human body along which body movement causes neither stretching or contraction. Discovered by Arthur Iberall in work beginning in the 1940s, as part of research into space suit design,[1][2][3][4] they have been further developed by Dava Newman in the development of the Space Activity Suit.[5]

They were originally mapped by Iberall by drawing a series of circles over a portion of the body and then watching their deformations as the wearer walked around or performed various tasks. The circles deform into ellipses as the skin stretches over the moving musculature, and these deformations were recorded. After a huge number of such measurements the data is then examined to find all of the possible deformations of the circles, and more importantly, the non-moving points on them where the original circle and the deformed ellipse intersect (at four points per circle). By mapping these points over the entire body, a series of lines are produced.

These lines may then be used to direct the placement of tension elements in a spacesuit to enable constant suit pressure regardless of the motion of the body.[2]


  1. Jenkins, Dennis R. (2012). Dressing for Altitude: U.S. Aviation Pressure Suits, Wiley Post to Space Shuttle. US National Aeronautics and Space Administration. p. 241. ISBN 9780160901102.
  2. Dava J. Newman (March 2005). "Astronaut Bio-Suit System for Exploration Class Missions" (PDF). Massachusetts Institute of Technology. Archived from the original (PDF) on 2010-06-13.
  3. Iberall, A.S., "The experimental design of a mobile pressure suit", Journal of Basic Engineering, Transactions of the ASME, June 1970, p. 251-264
  4. Iberall, A.S. (November 1964). "RAND Development Corporation Report AMRL-TR-64-118: The Use of Lines of Nonextension to Improve Mobility in Full-Pressure Suits" (PDF). Behavioral Sciences Laboratory, Aerospace Medical Research Laboratories, Aerospace Medical Division. Air Force Systems Command, Wright-Patterson Air Force Base, Ohio.
  5. Maggie McKee (17 July 2007). "Future spacesuits to act like a second skin". New Scientist.

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