It depends on the class theme, the clients participating and the overall goal you are trying to achieve. I teach all of these exercises and if someone has difficulty to perform any of them, then I just modify the exercises. Each person is different and I don’t like to eliminate exercises or movements from any program, unless it’s absolutely necessary.
Bear with me; this answer is a bit complex.
I would not recommend that a client perform a contraindicated exercise.
Having said that…the word contraindicated crates a problem.
What exercises should be contraindicated?
A person with an ACL tear would probably benefit more from closed chain exercises (squats) than open chain exercises (leg extensions). In this case, leg extensions are contraindicated.
However, leg extensions would not be contraindicated for people who don’t have ACL tears and need to strengthen their quadriceps.
What Karin and Esta said is true… one exercise can be appropriate for one person but inappropriate for another.
Sorry for the long explanation.
Hope this helps you out!
For group exercise classes, where there is a large group of people and I haven’t assessed any of them, I follow the AFAA and ACE rules on contraindications for group exercise classes.
For personal training, I look at the goals – short term, long term, and function – of the person I’m training. I might have an individual do a movement that is contraindicated in a group-ex class, but if it supports their daily activity or sport. Although it happens occasionally, I don’t typically train competitive athletes for sports performance. I train regular individuals who might include a sport as recreation but are interested in sustainable health.