I fell into the same trap a few weeks ago. After either riding outside or using the trainer 4 times a week and doing 2-3 miles on the elliptical twice a week, I thought "no big deal" when my daughter asked me to go jogging with her. We did just less than a couple of miles and I stayed with her the whole time. When I got up the next morning, I was able to identify every leg muscle that is not used for cycling by the amount of soreness. Oh well, I have now added jogging to the weekly routine.
Also, I now have even more respect for tri-athletes.