Watch the Musical Mind & Stress online guitar lesson by Bruce Arnold from Guitar Physiology Survival Guide
As your musical mind develops, it gains the ability to recognize sounds and connect them to your guitar. This interfacing with the flow of music is dependent on your ability to "hear" music. Therefore along with a physical technique, developing your ears through ear training work is crucial. Not hearing what you want to play or what you are playing causes stress, both mental and physical.
Stress causes your muscles to tighten up and will cause you to tense up no matter what techniques you use to play the guitar.