It is dangerous to perform CPR on a person who is breathing normally.
These chest compressions create significant local blunt trauma, risking bruising or fracture of the sternum or ribs.
If a patient is not breathing, these risks still exist but are dwarfed by the immediate threat to life.
For this reason, training is always done with a mannequin, such as the well-known Resusci Anne model.

The portrayal of CPR technique on television and film often is purposely incorrect.
Actors simulating the performance of CPR may bend their elbows while appearing to compress, to prevent force from reaching the chest of the actor portraying the victim.
It is dangerous to perform CPR on a person who is breathing normally. These chest compressions create significant local blunt trauma, risking bruising or fracture of the sternum or ribs. If a patient is not breathing, these risks still exist but are dwarfed by the immediate threat to life. For this reason, training is always done with a mannequin, such as the well-known Resusci Anne model.
The portrayal of CPR technique on television and film often is purposely incorrect. Actors simulating the performance of CPR may bend their elbows while appearing to compress, to prevent force from reaching the chest of the actor portraying the victim.
Cardiopulmonary resuscitation