Absolutely nothing. Provided that I eat appropriately to my activity and my chairs are always somewhat uncomfortable.
But if I spend a year working from chair as deeply reclined and comfortable (and position fixing) as this one: http://www.healthyback.com/products/Humantouch/Pc095-perfect... I get back pains because small muscles around my spine get weak and can be overstretched and damaged when I lift a fridge or something or just twist rapidly in some unusual direction.