THE TRUTH ABOUT STRETCHING
Not to oversimplify a complicated topic, but if you believe that stretching - of the kind recommended by the vast majority of health care professionals - is necessary for the health and integrity of the human musculoskeletal system - I have but one question for you.
WHAT ARE THE CONTRACTILE OR LENGTHENING PROPERTIES OF JOINTS?
The oft cited purpose of stretching is that it 'increases range of motion'. If that's true, how does it achieve this feat? To take a simple example, the elbow can flex and extend, as well as pronate and supinate the forearm.
If you can fully flex and extend your elbow, what could it possibly mean to stretch the elbow joint, or the biceps and triceps? It's a meaningless statement. If my biceps are operating at 100% strength, I can forcefully and completely flex my elbow, to the point where my fingers can touch my clavicle, and I'm said to have 100% range of motion. The mass confusion surrounding the idea of stretching is centered on an ignorance about the difference between functional range of motion, and stretching.
Absent some kind of pathology or trauma at the elbow joint, the only controllable element worth caring about, is the strength of the muscles that cross and control the movement of the joint.
The musculoskeletal system is comprised of contractile structures, and non-contractile structures. Muscles and tendons have contractile and elastic properties, ligaments and cartilage do not. If I extend my elbow 100%, to the point where my arm is completely straight, there is no longer any tension being placed on my muscles. If I over-extend because I mistakenly think this is good for me, then 99% - 100% of the forces travelling through my arm are being placed directly on my ligaments and cartilage - WHICH HAVE ZERO CONTRACTILE PROPERTIES.
This is the same principle as locking out under a Leg Press.
It's extremely important to understand that human evolution - as it relates to physical performance - doesn't give a damn about your preferences. If you have a goal of being able to perform an 'Eight Angle Pose', sorry, but you're objectively wrong. Repeatedly forcibly rotating your Lumbar vertebrae will either; A) cause immediate pain and or injury, or B) gradually reduce the integrity of the non-contractile structures stabilizing your spine, leading to chronic functional impairments and chronic pain.
Either way, evolution wins, you lose.
What's worse, is that stretching only lengthens your muscles in the sense that your perception of the pain caused by stretching is attenuated, thus allowing for greater PASSIVE - not volitional - range of motion at the joint in question. Passive R.O.M. simply means that a therapist for example can move your joint further after your having stretched it. You won't gain any additional active R.O.M.
So if you're trying to optimize your range of motion, just remember the term 'functional range of motion'. If your joints already have complete mobility in each appropriate direction, focus on the strength and integrity of your muscular tissue. There will always be specific morphological differences between individuals, as well as between men and women. Different people will respond differently to varying degrees of stretching. For the average person however, the most important thing to consider in order to optimize range of motion, is the strength and stability of the joint in question, not your ability to have your heel touch the back of your head.