What is the appropriate POPULATION?
For whom is this exercise appropriate and how can it be modified to accommodate a variety of fitness levels?

There is a plethora of different Special Populations; pregnant, amputee, older adult, osteo, neurological, diabetic, cardiac, physically or mentally challenged, overweight, children...the list is endless. You are likely to work with many different types of clients as a health-fitness professional and as a result you are expected to know and adapt your exercise and movement prescription to suit such.

Often in one class you can have multiple Special Populations. As a result you need to always screen your classes before every session to be aware of any special needs. Then you will assist these individuals to do movement appropriate to their special needs that doesn't cause harm, impede their natural abilities, or contradict requirements their medical specialists have requested.