can i mess up my muscle memory if after practicing for about an hour i start improvise and sometimes tense up because i'm playing faster than i'm capable of playing relaxed?
If you're playing something different than what you were originally practicing and trying to speed up then you should be fine.

The key is to make sure you're doing things perfectly; rather than teaching yourself the wrong technique and speeding up and working around it, make sure the technique is perfect and gradually work your way up. There's no secret; the better you practice the better you'll play.
ya, what happens is that i'm improvising or writing a new song and trying to pick a line really fast or something and my picking arm tenses up. is that something that i should completely avoid? (i.e. play the song i'm writing slower until i can play it perfectly relaxed?) i know that the end goal is to play relaxed, but sometimes to get the music that's in my head out and into the guitar i have to play faster than the level at which i'm relaxed at the moment. is something like that messing up my picking technique or could it have any bad consequences?
When you're practicing, you should be aware that every time you do something,
either wrong or right, that gets reinforced. So, "don't practice your mistakes".
In practice, you want to make sure you're adding up the positives way more than
the negatives.

When you're playing, just think about the music. Yes, you'll still be reinforcing things
either way, but the hope is that you do that so much in practice it, the positive will
start to dominate without thinking about it any more.
i hears ya.

thanks for the advice.

i just wanted to make sure i wasn't f-in myself when i played

thanks guys