I have never had back problems before, but these last couple days my lower back is really stiff and slightly achey. It doesn't bother me too much when I stand or walk, mainly when I bend and sit. It also felt fine yesterday when I did IMAX. I'm wondering if the side plank dips are the culprit, or that I lifted too much when I did deadlifts? Anyways do you think I should lay of aerobics today, even though it doesn't bother me when I do step aerobics and today is upperbody work, but should I avoid that? I hope this is a temporary thing. Any feedback?