Definition - What does extension of the elbow mean?
Extension of the elbow refers to straightening the forearm by widening the angular distance between the hand and the shoulder from a flexed position. Elbow extension requires the triceps brachii and anconeus muscles to perform the requisite range of motion until the elbow joint locks at zero degrees of stability preventing further movement beyond this point. In non-medical terms, this means that a person straightens his or her arm so that the elbow joint is open and not bent.
SureHire explains extension of the elbow
Extension of the elbow is the curvilinear movement by which the biceps brachii located at the front of the upper arm relaxes while the triceps brachii and its concomitant muscles located at the back contract by pulling the arm down from a flexed position straightening the elbow and increasing the angular range of motion until the elbow locks into place. In other words, straightening the arm so that it is straight and the elbow joint is not bent.
However, it is possible in some circumstances to hyper-extended the elbow joint by bending it beyond its normal range of motion. This can result in painful tears of the ligaments and, in severe cases, bone fractures. Some common causes of injuries related to extension of the elbow are falls where someone reflexively uses an outstretched arm to cushion their body from impact and results in greater trauma by risk of hyper-extension of the elbow. Attempting to lift too heavy of a load can also result in injury if the load exceeds elbow strength and control of the load is lost.