i was riding for about 4 hours solid on a 4x/freeride track and halfway down my last run my arm started to cramp up, my hand went into a fist and wouldnt return to normal, and when i pulled it out straight it would suddenly close up again. i had no control over this. about ten minutes of stretching it returned to normal...but the weird thing is there was no pain what-so-ever.

i was just wondering if anyone else has had this happen to them when riding and if anyone has some tips to prevent this.

Hydration will help. So will stretching and strength training.

Watch for poison blow darts... sometimes the forest folk just want to mess with you.

nasty bastards

That's great. Next time I go out on the trails I'll have to remember to bring a shotgun.

Pygmies in Michigan? Is this an unforeseen side effect of global warming?

Be sure to drink lots and get enough magnesium, sodium and i think potassium in your diet. I know magnesium is good for keeping free of muscle cramps... I take a calcium magnesium vitamin every day and i barely ever get muscle cramps.

Stay hydrated!

it could be because your muscle memory went into overdrive...considering a 4 hour run of holding on to the handlebars pretty hard with your arm stretched out...its likely that your are was just resisting returning to a normal relaxed state.

a banana for breakfast, and a banana when you finish riding should help keep the cramps away...

the runners remedy. + a bagel

I had exactly the same experience after a hardcore weightlifting session with lots of arm exercises. What you want to do is buy a sports drink, gatorade or powerade are good, you need to restore the electrolytes in your body, and keep hydrated, don't go crazy on the water though because it dilutes your electrolytes and you lose muscle performance. Also, 4 hours man? I hope you're kidding, that can't be healthy.
ciao