Hand, not hands and I'll elaborate on that shortly.

I've been getting serious numbness in my right hand and, to a degree, up to my elbow for the last month, maybe 2 but not longer than that.

I'm not new (started on 10 speeds back in the '70s) and I know about changing placement. Little help except riding no handed. I have not changed contact points nor have I changed my overall position. Only changes I can think of that more or less correlate to the problem is switch to Speedplay pedals (from Looks) and some decent weight loss. The loss was not a crash diet though but a steady gradual decline of about 25#.

Why hand and not hands? B/c of a motorcycle accident I ride essentially one handed. I am not an amputee but my left arm has minimal movement and I have no use of my left hand. However, this happened a long time ago (20+ years) and I've been riding since then.

I don't know why I'm having this problem now and know I may have to go looking for professional medical advice but would appreciate any thoughts anyone might care to share.

Maybe its because you are getting older. As you age, the body changes whether you like it or not. That means a change up on things like the bars. More spacers and then you know its that time.

Look pedals have a tall stack height, Speedplay a short stack height. Did you lower your saddle with the cleat change? If not, you may be overextending your leg, making your hips rock, and stabilizing with only one hand. That could increase hand loading.

Or on a simpler note, any chance your brake hood has rotated in, or your stem to bar clamp loosened? I find minor wrist angle changes leading to sudden hand numbness.

Do you have any numbness in your right hand at any time off the bike? If not, sounds like a fit issue that you need to address. Since you switched pedals, make sure your seat height is correct as mentioned above. I recently bought new shoes and had to do the same. If all is good there, slightly rotate your bars to bring the hoods closer to you and see if this slight change in position takes some pressure off your hand. Good luck figuring this out.

When does the numbness set in and when does it subside?

It could just be age. I hope not.

I have had a little bit to of tingling in my arm while weight lifting but nothing like what I get while riding and have lowered the intensity in the gym to offset that.

Will double check seat height as I did not adjust after the switch to Speedplays. Will also consider bar rotation. Thanks!

1/2 hour to 45 minutes into the ride. Will subside fairly rapidly if I sit up and ride no-handed for awhile but returns shortly afterwards.

The right answer is to see your doctor.I'm a recently retired US Army Occupational Therapist. I spent 20 years treating patients with numbness in the hands as a hand therapist both pre- and post-operatively. One of the first things that you should also do, is determine just exactly which fingers are going to sleep. The nerves that supply sensation do so in very specific patterns and can many times determine the correct course of treatment. For instance if the ring and small finger are getting numb, the problem could be in your elbow, if it is the other three fingers only, then it could be in your wrist. Or the problem could be higher up in your body - like in your neck. Thus the necessity for an accurate diagnosis from a physician.

Oh yeah, I figure the MD is in my near future. Figured there would be no harm in trolling for a few easy to implement ideas (such as the stack height difference mentioned above) beforehand. Sometimes, you get lucky and the solution is simple. Not often though.

Are you right or left handed? My left hand will tingle on intense rides. A sports PT said that I likely apply more force with my dominant leg and cause my non-dominant hand to do more work. Now when that happens I try to push with my right hand and after a few minutes my left hand stops tingling, and I notice my left foot drives harder.

...just a thought.

I was right handed prior to the accident, fortunately. Nowadays, I'm pretty much only right handed.