When I was a teenager I read the Electric Kool-Aid Acid Test, in which the muscular physique of Ken Kesey is described. Practically all my other heroes (Red Hot Chili Peppers, Monster Magnet) were pretty muscled, so I wanted to get buff myself. Beefcake! So I started going to a gym, drinking ginseng extract and raw egg yolk.
But very soon (within a year) I completely changed my lifestyle into an ascetic one, and though I still did some stretching (yoga) I eventually became quite skinny again.
Then in 2003, while I was working in a vitamin store, I read about a 12-week program, called Fit For Life. I decided to try it out myself, though not in a gym. I would get very stoned, put on Korn, Marilyn Manson or Monster Magnet, and lift weights at home, or pull myself up at the playground. This time I got my protein from delicious protein shakes and bars, and I supported the whole process with vitamins, minerals, creatine etc. I became stronger and more muscular than I had ever been in my life, and it felt great. Then in 2004 my back, wrists and left shoulder started hurting, so I had to stop for a while, but I picked it up again in 2005 with adjusted exercises.
In January 2006 I started feeling another type of pain (not related to exercise, disease or injury). That pain debilitated me for several months, until I realized it wouldn't go away, so I'd better start doing things again. And indeed the pain is still here, and it makes me avoid standing up, or to do exercises. It also makes it quite uncomfortable to sit, and while lying down during my six hours of sleep I have to shift my position all the time. This of course has made the pain in my back only worse. So...I hope I'm not turning into an invalid. I'm already an invalid in many ways. I would be so much more active on this forum and elsewhere, and do more trips, if it wasn't for the constant pain.
But back on topic: I think physical exercise is very important, especially for psychonauts. Perhaps it isn't essential, but when you're strong and vibrant, it benefits your study and it benefits your trips.