I did the second part of my work out on Friday- upper body. I don't know why but it was really hard hard!! I didn't increase the weights much- just the lat pulldown, and the only other difference were the pushups- using the bosu. However- I think I really worked to the limit and now I'm sooooooo stiff!!! Other weeks I haven't been as sore so it's a bit of a mystery why this one was so hard. The day before I did my legs- and they are also complaining!!