Professional assessments are the only reliable method for determining an individual's levels of health-related fitness.

The given statement is true.

Explanation:

Professional assessments are nothing but training a person to do or complete a work in a good and professional manner. Professional assessments are one kind of way to make the person or individual do all the respective work in a skillful and professional manner.

They are a reliable method to improve certain qualities of an individual and can be considered as the only main method to determine the health related fitness of an individual. There are no other health methods that can be used to determine the heath level of an individual. Hence the above provided statement can be concluded as true.