Depends on the injury. I have an older knee injury from 1998 but it didn’t take long before I was cleared for full exercise.
Many times it’s an issue of not being cleared to bear full weight on the knee or the knee is in rehabilitation. That determine whether they can handle a bike, treadmill while walking, an elliptical, etc.
I have found that many clients know what they can do and what they can’t, but be sure to test and assess.
Has the person been cleared by his orthopaedist and/or physical therapist to exercise with a personal trainer?
If so, the personal trainer ought to be in communication with the physical therapist and/or orthopaedist.
How long ago did the injury occur?
Too, personal trainers should be very careful when training individuals who are recovering from injuries. Even with the advice of a physical therapist,
1. If the personal trainer does not truly understand the anatomy and biomechanics of the joint involved;
2. If the personal trainer does not understand the impact exercise has on the injury;
3. If the personal trainer doesn’t know what exercise tests should be undertaken with the individual and;
4. If the personal trainer is not able to identify warning signs that the client is in need of a professional evaluation
He/she should not be training the individual.
If in doubt, use an upper body ergonometer. If that is not available, I recommend to people to use the ‘old’ Schwinn bicycles with the arm levers.
If otherwise cleared for exercise, starting with aquatic exercise is a good option.
You use a rather generic term ‘knee injury’. Do you have any PT advice? That’s where to start. If you are looking for land-based exercises, it will have to be in dialogue with the client and what works for them. It is always most important to start on new modalities for a very short period of time and judge about it the next day even if nothing has been bothering during the exercise itself. Then take it from there with appropriate progression.
It would depend on the injury. I would do an assessment or an evaluation on where the knee hurts. If the knee hurts where the petela tendon is I would not do any high impact. If the client is able to walk slow down the belt on the treadmill and increase grade to keep the intensity all relevant. If the outside of the knee is hurt, maybe have them do a gait analysis to see if they are over pronating. If they are maybe they have too high of an arch in their shoes. If you have any questions just ask.