Which stretching technique triggers the muscle spindles to respond with a contraction (i. e., stretch reflex) and an increased resistance to stretch in the targeted muscle group?

Answer;
Ballistic technique.

The ballistic stretching technique triggers the muscle spindles to respond with a contraction and an increased resistance to stretch in the targeted muscle group.

Ballistic stretching is a intense stretching method that uses bouncing movements to push the body beyond its normal range of motion. This technique stretches muscles much farther and faster unlike in static stretches, which are performed slowly and gradually. 

Generally travels west to east but often shifts to north and south