Is it age or is it the miles?

Over the past two days, I have wondered:  how many miles can your body (especially your legs) tolerate?  There has been a thought that an individual only has a finite number of miles in his/her legs, and it is the cumulative mileage over years that causes the decline in performance.  That's why those people who were the fast runners in their early years may not be the fast runners in the upper age groups (with some exceptions, of course). Why am I thinking about this, you ask?  Simply put:  I'm getting slow.  3 days ago, I had a fairly easy run, cruising 10 miles at (what is now) a moderate pace, a hair under 7:40/mile.  Felt good, finished feeling fairly refreshed, etc.  Waking up the next morning, my legs felt a bit tired, but I knew that it would be an easy recovery run day.  Well... it was a slog of a run in the trails for 5 miles.  I never felt very good during the entire run, as my entire body felt "tight."  I finished with some strides, and that made me feel a little better, and left me looking forward to the next day's track workout.

Stepping onto the track yesterday, I felt okay.  Rarely do my legs feel bouncy anymore, but I've come to accept that.  What I'm having a difficult time accepting is the speed at which I now run intervals.  My previous quote:  "never did I think I would be working so hard to run so slow" was never as true as it was yesterday.   I keep hoping that my fitness will have a breakthrough, and, all of a sudden, I'll be running fast.  And I also hope that, since I'm training for a marathon, my foot speed is slower because my aerobic fitness is good.  Nevertheless, it's not pretty to go through a 400 in 90 seconds, feeling like I'm working really hard.  I got through my 4 x 1200's yesterday, which were supposed to be at 5k pace.  Based on my intervals, my 5k time is right around 6:15 pace.  Guess what?  My last 5k was at 6:20 pace.  Sheesh.  I guess I need to realize that maybe the miles have taken their toll.  My other thought is that I need to lose some weight.  Late night snacking has put a few pounds on, and, although I have a difficult time reconciling this fact, my metabolism has slowed down a bit.  So, maybe the goldfish and the pita chips will need to go away for awhile.

 I related a "fun" workout I used to do several (well, okay now it's like 15) years back, where I would do 400's descending by 1 second each 400.  And I would warm up by running the first one in 80, then start at 75.  And it wasn't hard.  I think I'm going to try to get some foot speed back after the marathon.  I don't think I can ever do that workout again, but maybe I can get faster.  Either that, or plan to spend more time on the golf course!