There is a horizontal bar in the back that prevents the knees being bent. Get a tube of black 100% silicone sealant before you even start. (He needs them for school). If you are used to going to the gym and feeling the rock-solid construction of the gym equipment, then working out on a smaller, less sturdy piece of equipment like this Roman Chair will take some getting used to. Ive read many reviews here about issues with assembly, elevation, and noise. (French for ?That?s life? more or less. The second thing I noticed was the USB cable was thin, flimsy and had multiple kinks throughout. Would highly recommend these Dream Pairs sandals. I really wanted to make them work. Found it (shiny and spotless) among the clothes as i put them in the dryer.