I came across an interesting fitness blog post recently. It is a great point of thought, I make it a point, regardless of the program design for my client to ask how do they feel. Asking and listening to a client is very important and should determine how you proceed before training. How do you all address this subject with clients.
You have to remember that some people, because of what is ailing them, will always have pain. Say for example someone with Fibromyalgia; such a person will always be in pain. As Joanne said, use the pain scale (0-10). If the pain is 5 or over, don’t train that person. As suggested by our fellow professionals, if it is within your scope of practice, you should try to help that person.