The active supine biceps femoris stretch uses which physiological principle to increase flexibility

The answer would be: Reciprocal inhibition

When you contract a muscle, the muscle spindle receptor will send a signal that force the opposite of the active muscle to relax. This mechanism is called reciprocal inhibition. This will prevent a group of opposing muscle contract against each other, which could cause muscular injury.

Can you include the paragraph too ?

I’m going to go with b!