Which of the following methods of stretching requires an isometric contraction against resistance?

Proprioceptive neuromuscular facilitation (PNF) is identified as the correct method of stretching that involves an isometric contraction against resistance. This technique typically includes a partner or some form of resistance that allows the individual to contract the muscle being stretched while maintaining the position. The isometric contraction activates the muscle fibers, leading to an increased range of motion when the muscle is relaxed, allowing for deeper stretching.

This method works by taking advantage of the body's neurophysiological responses. When the muscle contracts isometrically, it activates the Golgi tendon organs, which are sensitive to changes in muscle tension. When the contraction is followed by a stretch, the inhibition of the muscle allows for an enhanced stretch.

In contrast, other methods like active stretching involve the individual using their own muscle strength to hold a stretch without the isometric contraction against an external force. Dynamic stretching involves moving parts of your body and gradually increasing reach, speed of movement, or both, while ballistic stretching uses momentum to stretch the muscles and can pose a risk of injury if done improperly. Therefore, PNF stands out as the method that specifically involves that critical isometric contraction against resistance, making it effective for improving flexibility and muscle function.