I was a little bit sore today and had iced my knees earlier, so decided to really take the "easy 4 miles" on the schedule seriously. I was able to head out about 6 p.m. The temps were toasty, but I wasn't worried - I was walking an "easy" 4. I walked to the library, did two laps at the park and came home - just about 4.4 miles according to Google. The last half mile I started to really feel tired. I slowed considerably and even walked with my arms straight down. Because my legs and knees had been sore and it was hot, I probably would have been better off sticking with 4 miles exactly. I'm sure I would have felt fine.
The worst part is, I took so long to walk, the CD was over! I'm in the middle of a great book, and had to walk several minutes wondering what would happen next.
(I iced my knees this evening and will again tomorrow. This happens every Spring and Summer because I don't do knee strengthening exercises year round. Once I build up some mileage and endurance I'll be fine.)