Question

what type of excercise can be hard on the joints​

Answer 1

Sit-ups I hear is hard on the back, I don't think people like these now a days.

Leg extensions as apposed to squats for quads I've heard about being bad for knees as well.

Answer 2

anything with running, jumping, twisting, forced stretching, can be hard on the joints, especially with arthritis

swimming is a good exercise to do if you have joint issues!