I reached the point where long motorway days were completely impossible because of the throttle position and the angle of my wrist over a long period of time. ( tingling and numbness in my right hand after about 30 minutes riding, particularly in cold weather)

Fixing up the throttle mechanism on my old Airhead helped quite a lot though, but in my case this little thing solved the problem completely, for just over 2 euros, once I found the correct angle at which to place it.... it's basically just a chinese knockoff of a "crampbuster", and does the job quite well.

It can be left on the handgrip and ignored until it is needed, it took a little bit of getting used to at the very beginning, but now I don't notice it's there anymore. It's very comforting to be able to keep the throttle open with the palm of my hand, relaxing my fingers completely, braking isn't affected, and neither is throttle return.

Electric Motorcycle Handlebar Refueling Aid Throttle Booster - US$2.99

Numbness in hands, wrists, arms can be evidence of more serious issues. Carpal Tunnel is one I had experience with. (still do)
I was a Boom operator (movie sound) 15 years ... that job really takes a toll on wrists (nerves, tendons). Many Boom ops get Carpal Tunnel syndrome ... well know in this job.

I went through the whole med system (good insurance back then) and had many tests and scans to determine if I did have Carpal Tunnel and how bad it was. Also did research following those who'd had Carpal Tunnel surgeries. For many, probably half ... it DID NOT solve the problem and in some cases weakened the person or made things worse.

In my case they determined it was not too far advanced. Also, one of the Doctors I consulted with admitted that Carpal Tunnel surgery may not solve the issues, recommended against it, but suggested I NOT do that sort of work anymore.

Because of this I did get numbness when riding. I also had severe "arm pump" problems during my AMA Enduro race career. I learned from a few AA Pro rider friends how they dealt with arm pump.

My 1st post above outlines their methods and the ones I used. Turns out doing all that also helps with numb hands. Funnily enough, one of the dumbest sounding, simplest and free techniques is one of the BEST! Stand up on the bike .... and B R E A T H !!!