leg "falling asleep"
 

I don't know if this qualifies as numbness, but that sensation commonly known as pins and needles or leg "falling asleep"
is a condition that arises with me at some point during every ride. I have tried a number of saddles and different angles and positions with these saddles, but even though some seats/angles work better than others the condition persists.
Yes, I do rise out of the saddle.
Yes, I do dismount at stoplights etc.
But sooner or later the condition will arise and once it does it stays or will quickly come back.
I have found that a more cushioned saddle tilted at a downward angle works best.
This leads me to believe that it is blood flow not nerve compression that is the culprit, but I may be wrong.
I am frustrated by this by this, because by 15 miles or so, the condition becomes really uncomfortable. I'm confined to <20 miles per trip.
I just ordered a selle SMP large trekking saddle from performance in the hope that the upward tilt at the rear and downward tilt of the beak
may take pressure off of the capillaries.
Any additional thoughts or suggestions will be greatly appreciated.

Its the nerves not the blood vessels ..

Is it more the leg, or the foot getting numb. If the foot, it could also be a shoe problem. With some shoes my toes get sort of numb after a while if I don't consciously remember to wiggle them around periodically. Combination of stiff soles and clipless pedals limiting foot movement I guess. I loosen the bottom strap (nearest the toe box) and between that and wiggling the toes, it seems better. Wearing socks that are too thick seems to aggravate it too.

Get off the Bike More Often?

definitely more the leg than the foot. Or perhaps I should say first the leg then the foot. It starts in the top thigh/butt area, then works it's way down. I ride platform pedals with 5 10 shoes that are a loose fit.

This does help, and I admit that I probably should start dismounting sooner, but I hate it.
I love to ride down lonely roads and just daydream and ride and daydream and ride. My endurance in terms of leg strength and wind could carry me further. It's the leg discomfort that is limiting me.

I had that problem at one time. A narrower saddle fixed it. Don't know if it was nerve or blood, but something was getting pinched. Therefore get rid of whatever it is that's causing the pressure on the inside of your upper thigh. Chances are that a narrower, harder, flatter saddle will fix it. My current fave only costs $40:

http://media.performancebike.com/ima...-BLK-ANGLE.jpg
Forté Pro SL Saddle

I had a selle anatomica which has no padding and is pretty narrow. Didn't help at all. I'm really at a loss as to which direction to go.

It's possible that you have a nerve or blood vessel that's getting pinched during muscle contractions. You might look at the descriptions and exercises here:
Gluteal Muscles, Psoas and Piriformis

We'd all find these stretches and exercises beneficial whether we have an issue or not. Preventative medicine is cheap.

I still think that a differently shaped saddle would be worth a try.

I have this happen occasionally, and its been going on for about 25 years now. With me, it happens during longer -- at least 10 minutes -- moderately hard to hard efforts. Once I ease up the pace significantly or coast, it quickly clears up. I've been to chiropractors, had a couple tests done (MRI, or something), but everything appeared to be "normal." So, apparently, its something some of us just have to deal with. I've fooled around extensively with my fit. While nothing cures it, it seems to be worse when the reach to the bar is longer, bar drop is more, and with a higher saddle.

^ sounds like a glute nerve entrapment issue, as more drop will increase glute engagement.

Excellent reference. Many of those exercises are ones my physical therapist has me doing. I did switch saddles, again......now using a selle smp and it is an improvement. I'm done trying out new saddles, I could open a flea market booth. It looks like the combination of glute strengthening, my selle smp saddle and getting out the seat more often is helping. I was able to ride 25 miles today. I can honestly start thinking of and training for a tour. This is a great time of year to live in Florida, I'm glad to be able to make the most of it.

First off: the most important thing is to go to a doctor to make sure that you don't suffer from nerve ailments or something degenerative that will only worsen.

I have a similar problem that I've been trying to chase down for the past year. I've been to bike fitters and physicians, ruling out some of the fundamental bio-mechanical issues that might be factors.

One physiatrist did take note that my right hamstring is weaker than my left. That was interesting to learn.

From my own experience with consults I've had, if it's happening to one leg only it's likely due to nerve compression, and not circulatory. I've been told that exercise can indeed help. I'm undergoing a regimen now that involves exercising the glutes and hamstrings. Hopefully things will improve.

What's helped me a little is this: lowering my saddle just a bit, moving my cleats back a bit closer to my heel, and concentrating much more than ever on a maintaining a level foot position as a I pedal. I've become more aware of my cadence and power output as a result.

It's still a recurring problem, but I've become better at regulating the issue.

I think that 50% of the issue is a mental problem: that is, not letting it frustrate you to the point where you don't enjoy cycling. Finding coping mechanisms and routines (including getting off the bike) to work yourself through it is key.