Question for guitar players

I figure there are a fair bit of those who play guitar, some of them even professionally in a band (like Calapia). I'm more of a multi-instrumentalist than a real guitarist, so I definitely hope that some of you could give me advice in one particular area.

Namely, barre chords. Have you ever played a composition that, for its four or five minute duration relies entirely on barring? I've found that even though my preference in terms of composition tends to favor bar chords, it's tough to play some of these pieces. My thumb often feels sore after playing a lot of the chords that require barring (my favorites are the suspended chords, wherein the (major or minor) third interval is replaced with the major second). Looks like barring puts a lot of pressure on the left thumb. How to come to grips with it? Does one need to practice the thumb muscle for that?

Thanks,
SM.