I am not so sure about the workout, but these definitely gave me a weird but sharp pain near my tail bone, of all the places!!!  First few days I wore them were fine, although I didn't feel any soreness in my thighs or calves.  But after wearing them for 5/6 days for about 1 hour a day, I developed a pain near my tail bone and it grew sharper as the days went by.  It felt like a nerve pain.  I kept fighting them, thinking they will go away.  But in vain.......  After another week of bearing the pain, I stopped wearing the shoes and immediately I felt a slight relief, and things got better from that point onward.  In 4/5 days, I was pain free again.  I am sure the fit varies for different people and not every one would experience what I did, but these definitely did not work for me.  And I decided never to give the Shape-ups a try, my pair of Clarks continue to serve me faithfully!