I don't know if this will help anyone here but I've been experiencing numbness of my hands and feet starting about 15 minutes into a ride when it's hot and humid for a number of years. This is partially a result of dehydration from sweating, although the hand numbness is 90% carpal tunnel syndrome. Anyway, today I was involuntarily forced to keep my cadence down and I didn't experience much numbness in my feet despite still losing a lot of moisture to sweating. My rear shifter has been having occasional issues where it might shift up or down only. Today it got stuck in the highest gear. In a 39-12 gear at the speeds I normally ride my cadence ended up averaging maybe 70 RPM. Normally I try to keep it at 90 RPM. I'm guessing this is too high for me, and it's part of the reason my feet go numb. I had thought the numbness was caused by pressing too hard on the pedals, which implies I should use a lower gear and higher cadence. It turns out the opposite is true. Evidently a lower cadence is more efficient for me. Besides not feeling numb, I ended up averaging close to 1 mph faster than usual. As for my shifter, the last time this happened I lubed it with light oil and it stayed fixed for a while. The problem might be bits of my old frayed cable stuck in the mechanism. In any case, I'm going to try to keep my cadence closer to 70 or 75, even though that feels like I'm pushing rather spinning. Even if it "feels" harder, my bike computer tells me I'm going quite a bit faster. I didn't experience much cramping in the legs, either, except when going uphill caused my cadence to drop under 60 RPM, and the pedal force to climb enormously. This is good news I guess, because my heart is barely ticking over at 120 BPM when my legs get numb or start cramping (this happens with a sustained effort above about 190-200 watts). Maybe now my legs can finally keep up with my heart/lungs.