We have the big punching bag by KWON, 180cm, weighs 50kg. The spring should be designed for up to 60kg bags, but bends even at our KWON neat long. No matter, still used, but now broken after 11 months (buy here in September 2013). Nevertheless 1 star more because the spring nunmal is a consumable item and for just under 10 euros can not be built for eternity - that will be no spring. The punching bag was also used almost every day for 1-2 hours. I now take another, we will see that there keeps better; On the one hand they should be so stretched already, even in the resting state easily, on the other hand not too much - difficult if you can not trust the manufacturer's instructions.