I've heard this before and understood it, but I didn't really understand it.
Due to my back issues, I haven't been doing all my training this week. I woke up this morning feeling pretty good so decided to go for a bike ride. I just chose my 6.5 mile route since I haven't been out in a couple of days and I have a race on Sunday. I felt really strong. I haven't had that good a ride in a long time. I felt strong and my cadence was up. It was great. I realized, strength really is gained during rest periods.
I'm still waffling about tomorrow. I want to do something since I've slacked this week. I don't want to do something because I have a race on Sunday. I do have tons of other things to do tomorrow so I'll probably not train. We'll see.