Popliteus flexes the knee joint and medially rotates the leg. It also laterally flexes and rotates the vertebral column. Flexor digitorum brevis flexes the middle phalanges. The brachioradialis flexes the forearm at the elbow. The hold compresses the legs, flexes the spine, and stretches the abdomen. When the forearm is pronated, the brachioradialis tends to supinate as it flexes. The brachioradialis is a muscle of the forearm that flexes the forearm at the elbow. The brachialis flexes the arm at the elbow joint. The flexor pollicis brevis is a muscle in the hand that flexes the thumb. A flexor is a muscle that flexes a joint. The leg flexes (tibia on femur) in the dorsal ventral plane. The gastrocnemius also flexes the leg at the knee. In a supinated position, it tends to pronate as it flexes. Once positive pressure stops, the diaphragm automatically flexes back to its original closed position. For example, your elbow joint flexes when you bring your hand closer to the shoulder.