I have some experience with this. Hope it helps.
If you feel like your finger/s are cramped and you have to physically pull them out straight then you might have a problem. According to the Dr's this is called "Trigger finger". It is most common in folks over forty who use mechanized machinery and tools, electrical saws and what not.
I have had this problem since I was about 15, I first got it after running a chain saw all day. I typically only got it after 6-8 hours of work so it really never bothered me, yet about 4 years ago I got a desk job where I'm not using my fingers everyday and now it takes about 30minutes for my hands to lock up, it takes about 1 hour on a bike or motorcycle.
What I have been doing is taking 4 advil before I do anything strenuous.
What happens is there is a serious of tendon sheaths in your fingers and base of your fingers,(these prevent your tendons from bowing) In my hands the sheath at the base of my finger swells up and won't let the tendon relax or slide through, thus my fingers are locked.
On the 28th I'm having a plastic surgeon slice these sheaths(Left hand only for the first round) in order to prevent it to open up when the swelling starts.
This is supposed to fix the problem. I have a severe case so IMO would just suggest the Advil(anti-inflammatory) before you ride.
The more vibrations the faster the swelling causes the cramping.
Hope this helps.