What planks, Russian twists and mountain climbers help to exercise

CORE

["Think about the central part of the body that these exercises target."]

The clue "What planks, Russian twists and mountain climbers help to exercise" leads to the answer "CORE" because all of the mentioned exercises—planks, Russian twists, and mountain climbers—are specifically designed to strengthen and stabilize the core muscles. The core muscles include the abdominals, obliques, lower back, and other stabilizing muscles around the midsection. These exercises target and engage these core muscles, making "CORE" the appropriate answer to the clue.