Do you lift weights?

I have the same problem, and I've been told it is because I lift weights. The same thing happens to my hands when I do long swims, like 1500m+. I've found that just wiggling my fingers around here and there, as well as shifting my hands from drops to hoods to tops while biking, helps quite a bit.

Of course if you have access to a massage, they can do wonders for this.