Just as with studio aerobics, seated aerobics have exercises that are "contraindicated". This term is somewhat overused and underutilized; it doesn't mean wrong, it just means that the specific exercise is inappropriate for either the general population or for the subject population. Again, this is not addressed to the needs of elite athletes who can benefit from these movements and not all disabled athletes will have problems with these movements, but enough of them will that I feel these have no place in a general seated population aerobics class.
As far as I'm concerned, the best synopsis that I've come across should be familiar to all of you certified by AFAA. The AFAA 5 Questions are:
These muscles may be unusable or only partly usable in athletes with spinal cord injuries. Spinal cord injury athletes may also have metal rods surgically implanted in their spinal cords to provide support and trunk stability. Stroke athletes may have impaired balance; twisting movements could lead to them losing their balance in a chair. For any athlete in a chair, the twisting movement could rub and lead to abrasion sores. Finally, these muscles are relatively small and don't produce a big oxygen demand, so you may not gain a large benefit from using them in aerobics.
This is an example where directly lifting the upper extremity movements from your step or aerobics class to a seated format may not be appropriate. Again, for those athletes with balance problems, this could tip them over. For athletes with coordination difficulties or with cognition problems, moving arms in opposing directions or in different motions is hard, requires more concentration and may result in frustration and cessation of exercise.
This does not mean that you are limited to moving both arms at a time; moving one arm singly is a good example of lowering the intensity level of an exercise. In that case, the athlete can use his other arm for balance or support if necessary.
Trunk Flexion is controlled by the Rectus Abdominus (the Abdominal muscles). Trunk Extension is controlled by the Erector Spinae (lower back muscles).
As with the torsional moves, spinal cord injury athletes may be unable to perform this movement, due to absence of control of these muscles or due to implanted spinal stiffening rods. Athletes with poor balance control may lose their balance and pitch forward. Athletes may lose their view of the leader when the bend forward. In all considerations, I would recommend against incorporating this movement into a seated class with disabled athletes.