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Perfect.

Before we get into some approaches to building grip strength for jiu
jitsu, I wanted to go over a couple of things. First of all, part of
grip burnout in a jiu jitsu tournament has to do with the lovely
cocktail of fear, adrenaline and technique that isn't exactly
thoughtful. To avoid burning out your grip before you even have a
chance to get started, you might consider not grabbing the gi from the
get-go but working some other type of takedown. Feel free to ignore
this advice if it's not your style (or if you're a judo player), but
if you're a wrestler grabbing the gi from the beginning does little other
than burn your grip and hurt your takedown attempt. You can also have
a light grip or use a no-gi approach where you grip the actual arm
(for example) rather than the gi to avoid killing your forearms before
you even have the chance to get started. Just something to think about
and possibly discuss with your coach and team.
Secondly, make sure you don't go nuts with the grip training. It is
very easy to overtrain, so make sure to either incorporate it as a
small part of your overall strength and conditioning program or, if
you're using a more intense approach, to take two weeks off every
month or so in order to prevent overtraining or injury.
Having said that, here's some approaches to strengthen the grip for jiu jjtsu.
Throw a gi over your pullup bar and do some pullups grabbing onto
that. If you're still doing jumping pullups or body rows, use a gi for
those instead. If you didn't bring your gi to the gym, you can use a
towel in a pinch.
Wrap a towel around your bar to make it nice and fat, and kill your
forearms by doing your pull-ups on that. You can also use a fat bar
for your barbell lunges, or fatten up your dumbbells for your one-arm
rows.
One simple way to work your grip strength is by lifting heavy things.
Take the lifting gloves off, use some chalk if necessary and work your
deads.