Flexion and Your Joints

Flexion is the medical term for bending an arm or leg. Techically speaking, it's a physical position that decreases the angle between the bones of the limb at a joint. It occurs when muscles contract and move your bones and joints into a bent position.

x ray of a person's knee
Peter Dazeley / Photographer's Choice / Getty Images


Hyperflexion occurs when a joint is flexed beyond its normal range of motion. When the joint is hyperflexed, it is moved beyond the maximum safe flexion. Such extreme movement can potentially result in injury issues to the opposing ligaments, tendons, and muscles. 


The opposite of flexion is extension, which refers to the straightening of a joint. In other words, flexion works to shorten a joint angle while extension works to increases it. Typically, a normal extension of a joint is limited to 180 degrees or less. In other words, that joint can basically be opened until it is straight. Think of your elbow or knee as an example, as these can be moved until they are virtually straight.


Further on the opposite end of the spectrum from flexion is hyperextension. Just as it sounds, hyperextension is an extreme version of an extension. You often hear that an athlete has suffered a hyperextension. This is what such a diagnosis is referring to.

Hyperextension is defined as an excessive joint movement in which the angle formed by the bones of a particular joint is opened, or straightened, beyond its normal, healthy, range of motion. So while extension of a joint refers to stretching it or straightening it within its normal limits, hyperextension refers to stretching it excessively beyond its normal limits, as determined by the range of motion. Bending of the joint in such a manner often results in injury issues such as ligament or tendon tears, or cartilage damage.

Range of Motion

A majority of the human body’s joints allow for some movement. A few particular joints, like joints in the skull, do not. Those joints that do allow for motion, such as the knee or ankle, have a predetermined range of motion. This range of motion is basically how far is each direction that joint can move or bend comfortably. The range of motion of a joint is usually measured in degrees. Each individual joint has a separate range of motion.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. TeachMe Anatomy. Anatomical terms of movement.

  2. The Free Dictionary: Medical Dictionary. Hyperflexion.

  3. Eidelson SG. Sprains - Strains - Soft tissue injuries. Remedy Health Media: SpineUniverse.

  4. Soucie JM, Wang C, Forsyth A, et al. Range of motion measurements: reference values and a database for comparison studies. Haemophilia. 2011;17(3):500-7. doi:10.1111/j.1365-2516.2010.02399.x

By Elizabeth Quinn
Elizabeth Quinn is an exercise physiologist, sports medicine writer, and fitness consultant for corporate wellness and rehabilitation clinics.