Whether a person's impairment substantially limits a major life activity depends on its nature and severity, how long it will last or is expected to last, and its permanent or long-term impact or expected impact.
Musculoskeletal disorders vary greatly in severity and degree of permanence.
Before the passage of the ADA, some employers attempted to screen out persons with disabilities during the hiring process out of fear that these people represented an undue safety and workers' compensation risk. Employers used pre-placement medical examinations to identify the particular disability the applicant had and then used this information to make a hiring decision. The trouble with this approach was that the candidate had no chance to show the employer whether he could actually perform the job. Specifically, employers may not inquire about an applicant's medical history before making a conditional offer of employment. After the job offer is made, an employer may inquire about a prospective employee's medical history or require medical examinations as long as this policy is applied consistently to all entering employees in a particular job category.