In reply to lewys-edwards:
If you fill a large (2 litre +) bottle with water and hold this in a pinch grip in one hand, with your knuckles parallel with the ceiling, flex the wrist to 90 degrees and lower again, repeating till failure. If you find it too easy or that it's taking too long, fill the bottle/a similar container with something heavier.
Also, get a stick, a brick and some string, tie the string around the brick and the rope so the brick hangs from the stick when you hold it in both hands out front, wind the stick round with your fingers so the brick rises, and unwind again.
Both of these exercises really help with wrist stabilisation, and doing reps of them will affect how quickly you're forearms recover from being pumped.
Also, in day to day life, try using your fingers to carry things, so that your forearm muscles are engaged. even when carrying things like shopping bags, people usually let them hang from the fingers, using the skeleton rather than forearm muscles. This way you can incorporate teeny weeny bits of finger training into your day to day life. Also it's interesting to see when someone starts moving furniture around open handed...
Hope these help!