Employers Obligation for Ergonomic Assessments

What is an employer’s obligation for employees in regards to ergonomics?  We are in an office environment and have received doctor’s notes from a couple of employees requesting an ergonomic assessment completed due to back and shoulder pain.  We have not been made aware of any inquiries to these individuals and they have not been off of work for an extended periods of time.  One doctor’s note states shoulder pain due to poor office set up.  We have provided tips for staff on how to make their work space more ergonomically friendly.  Further if it is recommended that a new chair or sit to stand desk is required, is it the employer’s responsibility to purchase it?