The word "extremity" refers to the outermost or farthest part of something. It can also describe a situation or behavior that is very intense, severe, or beyond normal limits. Full definition
As a result of the bombings, there were three fatalities and 264 casualties, with the most severe injuries involving lower extremities of those located closest to the blasts. (sciencedaily.com)
What this marching is going to do when I start hitting it and putting as much force into the Elite as I possibly can, that is fortifying the lower extremity of foot / ankle / plantar / fascia / achilles / etc. (weckmethod.com)
This structure is present in extremities such as the hind legs. (en.wikipedia.org)