One interesting idea in exercise and rehabilitation divides exercises into closed chain and open chain. Chains are links of body parts, such as foot, ankle, knee, and hip during walking. In a closed chain the end of the chain farthest from the body is fixed, such as a squat where your feet are fixed and the rest of the leg chain moves. In open chains the end is free, such as in a seated leg extension.
6 Closed Chain Exercise for Knees & Legs | AFPA Fitness
