Music used in thriller films

The music used in thriller films typically starts soft and quiet and then gradually gets louder and denser as the action intensifies to a climax in the scene. A good example of this would be the scene from Lord of The rings : Fellowship of the Ring, in the action scene leading up to Boromir's death. The music gets louder and more intense as the scene intensifies, and then suddenly stops when Boromir is hit by an arrow.
   

We plan to implement this same technique in our film when Alex tries to escape the thug who tries to beat him/ kill him.
   Even though action scenes are high in intensity and drama, classical music is very commonly, if not predominantly used in these types of scenes. One would think that intense music like Rock would be used, but classical music often gives the best effect.
   Another example of this would be in the standoff scene in The Good, The Bad and the Ugly, however in this scene the music is the device used to create the tension and drama. In reality, all that is happening in the scene is three men looking at each other in anticipation of the draw, however, the music makes the scene incredibly intense. The music get louder and denser as the scene gets nearer to the draw, and then stops Angel Eyes is shot by Blondie.