Door horizontal bar is dangerous if not secured properly!

In the beginning I fell along with the stretching rod very hard on the back and have drawn me on my butt and arms strong bruises and abrasions, because the rod slipped. After many attempts I have now the following solutions: If the door frame is smooth, roughen both the rubber rings on the rod and the corresponding locations on the frame with sandpaper, then clamp rod. Before each exercise check strength, also check whether the bar is slipped. Now for a few days, it works for me without problems.