A stretching board, also known as a slant board, functions by providing an angled, stable surface to stretch lower leg muscles, calves, and feet, increasing flexibility and range of motion, and helping to relieve tension and reduce the risk of injuries like plantar fasciitis and Achilles tendon tears. It is used in physical therapy and fitness routines to improve balance, muscle power, circulation, and overall posture by allowing for deeper, more controlled stretches than standing on a flat surface.