Definition of leg extension in US English:

leg extension

noun

  • 1A section that attaches to or fits inside a leg of an object allowing it to extend to a desired length.

  • 2An act or the action of straightening (and typically raising) one's leg or legs; (now especially) an exercise performed seated on an exercise machine with a weighted bar that the shins hook under, lift, and slowly lower.

Origin

Mid 19th century; earliest use found in American Artisan.