Differentiate open-chain and closed-chain exercises with examples in knee rehab.

• A. Open-chain involve distal movement; closed-chain involve weight-bearing; examples: leg extensions; squats.
• B. Open-chain are weight-bearing; closed-chain are non-weight-bearing; examples: squats.
• C. Open-chain require isometric only
• D. Closed-chain never involve joint movement

Answer: (A)

The main idea is how open-chain and closed-chain exercises differ in distal movement and weight-bearing during knee rehab. In open-chain movements, the far end of the limb moves freely and the limb is usually not weight-bearing. A leg extension is a classic open-chain exercise: the foot moves through space as the knee extends, while the body weight isn’t supported through the leg.

In closed-chain movements, the distal limb is fixed against a surface and the body moves over it, meaning weight is borne through the limb. A squat is a typical closed-chain exercise: the feet stay planted, and the knee, hip, and ankle move together with the knee bearing load.

That’s why this option is the best: it accurately links open-chain to distal movement and non-weight-bearing, and closed-chain to weight-bearing, with leg extensions as an open-chain example and squats as a closed-chain example. The other statements misrepresent these ideas: open-chain isn’t defined by weight-bearing, isn’t restricted to isometric work, and closed-chain movements do involve joint movement.