Flexibility could be defined as the ability to use your muscles across a wider variety of positions and in a variety of different ways. For instance, you have greater flexibility if you can anchor your hamstrings by creating stability at either your feet/ankles, knees or hips. 

You can also have greater flexibility if you can feel your hamstrings (and the muscles they work with) as well as control them, relaxing them or activating them at will.

The sensational in the title of this book refers to the sensations that muscle generates when it is active (and the lack of sensation that occurs when muscle is relaxed.) Thus muscle acts as both an actuator and a sensor. Sensational also refers to the sensation that connective tissue generates when it is stretched or otherwise under tension. 

Sensational hamstring stretching teaches you how to feel and control the hamstrings and other muscles that work on your hips, knees, lower leg and torso so that you can work intelligently towards improving your hamstring flexibility.

Why is this an intelligent approach? Normally we have to rely on outside resources to tell us what to do. By building body awareness from inside and taking the time to look back on our experiences afterwards, and by learning to feel and control our body while we use it we can improve our understanding of our body and work figure out which muscle control patterns to use on any particular day to improve flexibility.

Problem solving and analysis is required. It’s a lot like learning to program. Or it’s like learning how to paint or draw or sculpt the human body. Or it’s like figuring out why a particular system isn’t working (and how to fix it). The end result isn’t just more flexible hamstrings, but a greater ability to sense and control your body and apply that in anything that you are doing.