I just got an unpleasant wake up call during jury duty. Flat ground cruising does not translate to multiple flights of stairs. The three miles of street or hallway walking did not affect me the way climbing stairs did. I also discovered that I needed new shoes, and a lighter EDC if I'm only carrying on one shoulder.

What type bag are you using for EDC? I use a backpack often on one shoulder but could easily switch to both shoulders.

An old business messenger bag, roughly equivalent to a California Pak Negotiator briefcase, with a memory foam seatbelt pad for the shoulder strap. Normal loadout is about 3 lbs, but with the extra stuff I was carrying (vest, water bottle, and coffee mug), it weighed closer to 6 lbs.

I'm ambivalent about backpack vs. messenger bag. A messenger is easier to wear over a coat and access the contents while wearing it, and is slightly more professional in a meeting. But, it's limited ability to carry more then a few lbs comfortably hamper it for anything other then office use.

For years I have carried a combination briefcase/backpack somewhat like this: http://shop.eaglecreek.com/everyday_bags_view_all/l/329 .

Mine works nicely works in a variety of environments. The packstraps tuck away nicely with just enough room in the pocket for survival rations (chocolate bar).

My work is fairly casual and a backpack is fine. If I needed formal I'd find a suitable backpack in basic black

I think that's the way to go. I'm an engineer in a business casual office. I'm also the only guy left in the office who still carries their own briefcase. Everybody else carries laptop backpacks for personal bags, and a selection of padfolios/portfolios, clip boards, and writing/computation pads for business.

+1 on the fitness; regular walking, stairs and distance

Be careful to listen to your body. I've been pushing mine a little too hard with daily hiking, and flared up a nagging knee injury because I was stubborn - and a little addicted to hiking. Denial can hurt.

From what I have been able to determine, it is not how much you do in a day, but doing something nearly every day. In fact, it appears that the minimum is much less than we may think; that in fact, 30 minutes of "moderate" exercise 5 days a week is what will get us by. So don't train for the Olympics, and as you said, listen to your body.

Check ScotteVest products. I don't carry any bag/pack anymore. Everything I EDCing fits into the SeV vest (or SeV jacket the other time) pockets. The vest distributes the weight evenly over your shoulders, I believe, even better than a backpack. Everything is at hand, unnoticeable to me and to others, and the weight of the "bag" itself is precisely zero. The shoulder bag is plain dangerous as your spine is never straight because of the load's asymmetry. One day I looked in the mirror and noticed that one of my shoulders is higher than another. It took 5 years of special spine exercises to revert that. In the long run that may turn into other, more serious spine problems.

For the stairs - sure thing it's not translating, as there are different muscles working on ascend and especially on descent. Last weekend I've been hiking for 10.6 miles, with the 800 feet gradual climb. The way up felt like nothing at all to me, but descending back to 0 I had to use my hiking stick for every step after just 10 minutes of walking down. At some point I figured that I can walk without any pain turning back first, and looking over the shoulder, but that was not really safe on that trail. So, I had to invent a special long stride step involving the stick to speed up the descent while minimizing the pain. Fortunately it was a steeper trail (not the same as the ascending one), so it took not too much time and I was back to the parking lot shortly before dark. The GPS tracker showed my ascending trail speed at 3 mph, descending - just 1.2... Only by yesterday's evening I started to descend on the stairs normally without the severe muscle pain.