When does an injury arise out of and in the course of employment?

An injury arises out of the employment relationship if the cause of the injury is causually related (arose out of) the workplace environment. The injury occurs in the course of employment when it occurred during the performance of work related duties. In many instances, it is clear that an injury is work related enough to be covered by workers compensation. For example, if you fall and injure your leg at work that injury arose out of the employment relationship and constitutes a compensable injury.

However, let’s say that you are at work and suddenly have a lot of back pain. Is the back pain caused by your job or is the back pain caused by activities you have done outside of the work environment, such as helping a friend move furniture to new lodgings?