Note: There are special rules for a child that is the qualifying child of more than one person. Do research or get professional advice if you encounter this situation. Qualifying Relative. All of the following tests must be met to claim a dependency exemption under the rules for a qualifying relative.
Reduced ability to decelerate due to pain, fatigue or structural damage at any of these stages will put increased force through the next stage, setting it up for injury. So, my hypothesis regarding Djokovic and Murray would be that reduced strength in the muscles around their scapula is putting more stress through the shoulder and elbow.
What's frustrating is that we all had that ability when we were in the womb. Humans are built, piece by piece, by embryonic stem cells, which are highly pluripotent -- that is, able to divide and differentiate into various other sorts of cells, from nerve cells to muscle cells to blood cells.