My "usual" run is three miles, basically around the block.
Today I was only able to run about one-third of the distance. My calves and hamstrings were locking up.
I attribute it to not stretching on my day off. I think I am going to have to stretch three times a day, every day. Each problem muscle group requires a minute. Since I am struggling with left-right/hamstrings-calves that is a minimum of four minutes stretching. In total, I will be spending more time stretching than running.
I guess a gotta do what I gotta do.