Riding a bicycle with my TKR

We've re-discovered a love for bicycling!  And have been riding daily after work, at least when the weather cooperates.  Our typical after-work ride takes about 45 min, and is usually about 3 mi or so in length.  We live at the top of a hill which is part of a series of ridges, so we're riding uphill and down. 

Early Saturday AM, before anyone else in the house was awake, I decided to explore a new bike path just to see what it was like.  Turns out the short route is about 6 mi, with the first mile being almost entirely uphill.  I certainly learned to use the gears on the bike for this one, although I still have a problem understanding why a bike has to have 21 (or more) gears.  I probably use a total of 8 gears at most, and then only when there is a long steep grade.  Otherwise, I'm using maybe 3 of them?

My legs were like jelly when I got home, and I did have to walk the bike up one short-but-steep grade.  But for the remainder of the ride, I was on the bike, and sitting down, using the gears on the bike.  There was no pain, either in the knee(s) or in the supporting muscles.  However, by the end of the day, my legs did feel very tired, so much so that I came in from the gardening much earlier than usual. 

Could I stand up and "pump" going upgrade?  Yes, although my sense of balance is not good enough to ride that way for very long.  I'd certainly NOT want to ride that way uphill and in traffic.  But I can do it. 

I'm working on a long post in celebration of my upcoming 8th month TKR anniversary.  It's very clear to me that I have been extremely lucky with my TKR.  I will take this opportunity to post the positives, the negatives, and the things "I wish I knew BEFORE my TKR".