Months ago I did some fill in work for a couple different bands at the same time, so I had to shed the crap out of unfamiliar tunes.. I must have overplayed for a period because after that I realized that if I play anything with a lot of pinky work (especially octaves) the palm muscle linked to my pinky gets fatigued very quickly! I've tried stretches and have always played with my thumb positioned on the back of the neck with a soft angle in the wrist (nothing extreme). I've also been working on octaves during my shed work to strengthen the pinky and stop when I get fatigued, but I don't notice any more endurance after all of this.. The only thing that "helps" is if I flatten my palm against the back of the neck, causing me to fret with the sides of my fingers as opposed to the tips.. It seems I could play octaves endlessly like this, but I don't think this is "proper" technique, and it doesn't seem very practical to play like that. Is there something I should do to help?