While dead hangs may be OK for people with good upper-body strength and no shoulder problems, they can be risky for others. People with shoulder hypermobility (excessive motion of the shoulder) or shoulder instability (such as those who easily dislocate their shoulder) may need to be cautious. The shoulder, by design, is a relatively unstable joint. It has a large ball-type bone called a humerus, which sits in a relatively small socket called a glenoid.
Source: Medical Xpress