EVERYTHING NEEDS TO BE TRAINED! But usually you can incorporate a number the stability and control muscles into a complex/multijoint movement.
AND EVERY CLIENT SHOULD BE STARTED OFF WITH THE FOUNDATION MOVEMENTS. Which are all of the movements naturally occuring at every joint. And the goal is to achieve balance and a normal ROM at each joint. Strengthening muscles around a mobility compromised joint can be unwise.
If you are interested in discussing this more, get in touch with me through my website www.hawaiifitnessacademy.com or my IDEA profile.