What is the burden of proving an employee has sustained a workers' compensation injury?

An employee has the burden of proving, by a preponderance of the evidence, that he or she has sustained a compensable injury within the workers' compensation system. ( Matea v. Workers' Comp. Appeals Bd. (2006) 144 Cal.App.4th 1435, 1443, 51 Cal.Rptr.3d 314 ( Matea ).) " "Although the employee bears the burden of proving that his injury was sustained in the course of his employment, the established legislative policy is that the Work [ers'] Compensation Act must be liberally construed in the employee's favor ( Lab. Code, 3202 ), and all reasonable doubts as to whether an injury arose out of employment are to be resolved in favor of the employee. [Citation.]" [Citation.]" ( Id. at p. 1444, 51 Cal.Rptr.3d 314.)