chaps, i'm interested to know...
does anyone find that your posture or command of your core musculature does odd things when you concentrate on challenging bits of playing?
i first noticed this when we did the MDB euro tour in 2012 - when i'm facing a tricky section, i seem to push my stomach out to meet the guitar. i can't work out if i'm going this to brace the guitar in place or whether it's that i lose ab or core control when i'm concentrating quite hard.
rather than it being merely an aesthetic / vanity-based concern, it affects my breathing control when i'm singing at the same time.
Never noticed myself doing anything like this. If anything I tend to hold my breath/not breathe enough while doing something tricky.