We have employees who are telling us that OSHA has weight limits for males and females as far as lifting requirements are concerned. I can't find anything and neither can anyone else in my department. Is this true?
OSHA has no specific regulations regarding lifting or any other ergonomic issue. That said, OSHA does has—and enforces—the "general duty" obligation to provide a safe and healthy workplace.
The OSHA expectation is that you evaluate safe lift limits and assure measures are taken not to cause injuries. If you are seeing repeated injuries on a specific task related to heavy lifting, OSHA could be expected to cite and fine under general duty if the company did not take corrective action.
The best guidelines are the CDC/NIOSH lift guidelines
. They are not mandatory and are by no means comprehensive, but they offer some help in determining a starting point for evaluation.