I am practicing tremolo picking at the minute and my hand is not tenced as it should be, but whenever i try to go a little bit quicker than usual my hand tences slighly shakes(cant control this) and then just gives up.
Is there any specific excersizes or runs that i can practice that will improve my tremolo picking.
Nothing you can do will make you pick faster if that's what you're focusing on. Stop pushing yourself for speed and work on the things that make up speed: relaxation, co-ordination and, most of all for your picking hand, economy of motion. Unless you're making small, relaxed movements you'll never be able to really push your speed at all.
R.I.P. My Signature. Lost to us in the great Signature Massacre of 2014.

Quote by Master Foo
“A man who mistakes secrets for knowledge is like a man who, seeking light, hugs a candle so closely that he smothers it and burns his hand.”

Your hand shouldn't be tensed with anything you play, if you're tensing to trem pick then you're not doing it correctly.
Actually called Mark!

Quote by TNfootballfan62
People with a duck for their avatar always give good advice.

...it's a seagull

Quote by Dave_Mc
i wanna see a clip of a recto buying some groceries.

How about chromatic scale which uses all four fingers, practicing trem picking on each finger? Slowly and as Mark say's, without tension in hand. Trem picking can go side to side, as well as up and down, play around with that as well. Side to side might reduce tension in hand, at least it makes sense in my mind without guitar in hand.
Quote by Pagan_Poetry
Sadly this is Ultimate-guitar, not Simple-guitar. We can't help you.

Yeah, that's what we like to call the limit of what you can play.

No matter how fast you can play, if you try to push past that, you'll get tense. You just need to keep practising and stay relaxed and that "limit" will keep increasing.
So practice tremolo picking with chromatics ? ,
Is that how most metal players start tremolo ?
I am usually play blues, rock and punk but wanted to try something a little bit more demanding
practice. use an obnoxiously light pick, and work your way up to higher speeds.
I'm a drummer, guitarist, bassist, songwriter, and vocalist. It's good to be balanced.
If you check out my channel on Youtube you can take a look at my basic videos on picking for a start. I don't yet have a video on tremolo picking, but there are many demonstrations on me doing it in the demo video and I should have a lesson on it up in the next few weeks. Basic Techniques
just relax while sitting and watching tv or something, grab a pick, and simply pick the air. wile not paying any attention to your hand. just watch tv. stay as relaxed as possible. its just like running or swimming, or biking, you gain speed as you work the muscles. but it doesn't work if you tense them up because it can cause injury to the muscles.
i guess to sum it all up, just practice.