If the translation is for the US, this might be what you're looking for:
29 CFR 825.312 - Fitness-for-duty certification.
Authorities (U.S. Code)
...(b) An employer may seek a fitness-for-duty certification only with regard to the particular health condition that caused the employee's need for FMLA leave. The certification from the employee's health care provider must certify that the employee is able to resume work.
US Code of Federal Regulations, https://www.law.cornell.edu/cfr/text/29/825.312

Fitness-for-Duty Certification
As a condition of restoring an employee whose FMLA leave was due to the employee's own serious health condition that made the employee unable to perform the employee's job, an employer may have a uniformly-applied policy or practice that requires all similarly-situated employees to obtain and present certification from the employee's health care provider that the employee is able to resume work.
https://webapps.dol.gov/elaws/whd/fmla/12a6.aspx

From the context given, it would seem that this company gives training in risk prevention in the workplace? In which case we are not really talking about their physical fitness, but rather this would be a certificate showing they had the competences required to prevent risks - in which case "certificate of competence" is a commonly used expression. I would need my assumptions of the context confirmed to be any surer though!