Hello: I ride a Specialized Stumpjumper. About 10 years ago, I had to switch to grip shifters from rapidfire due to pain from arthritis in my thumbs. Now, it's getting difficult to even use the grip shifters -- I basically stay in the middle front gear. Luckily I can still shift the rear gears. But -- something has to give!

What suggestions does anyone have? I never dreamed that what would finally make me think about giving up bike riding would be my thumbs!