The way I see it ...
Rate your pain before the exercise on a 0-10 scale.
During the exercise the pain might go up, and that's okay really.
What matters most when looking at symptom-reducing exercises (like McKenzie) is what does your pain feel like
when you're done.
So let's say that "Mary" has lower back pain. She rates it at a level of 6 which is pretty strong pain. She does some prone-on-elbows. Her pain goes up to an 8 while she is resting in that position. But when she's done, her pain is now a 3. To me that is a good exercise for her. (Especially if it also centralizes the pain, ie takes leg pain away and puts it in the back.)
However, let's say "John" also has pain at a level of 6. He does press ups and during the press up his pain is a 2. But when he's done, his back pain is an 8 and he now has leg pain. That is clearly NOT the exercise for him.
The hard thing about the back is that many different structures can cause similar pain. And more than one structure can be injured. For example, someone might have lifted with improper form, and pulled a muscle, strained a facet joint, and caused a small disk bulge. It takes good evaluative skills to determine which one is causing the most pain. And treatment for one area can aggravate another. It's a delicate balance.
And very hard to do over the internet.
