If you aren’t training runners using aquatic exercise, you are missing some of the best training opportunities for your clients.
I am an advocate of aqautic exercise for restrengthening injured runners and athletes. I also use it to train my clients that are not injured. Aquatic exercise is used in almost all professional sports programs for prehab, rehab and postrehab situations. And equestrian (horses) training facilities spend big money to construct pools/tanks for use to train multi-million dollar horses, both as training and rehab for injuries. It is even possible to train for power and hypertrophy using aquatic exercise.
If you think that aquatic exercise is too wimpy for you, I invite you to visit me on the Big Island of Hawaii. I’ll change your mind. This is one of the course formats that I teach as CECs for fitness professionals. Check out my website – www.hawaiifitnessacademy.com . And I would be happy to just meet any fitness professional coming here on vacation. This is my passion and I like to spread the Aloha in the fitness community.
Your question has lots of open answers. What is the etiology of the knee pain? What are the cardiovascular issues? What are the diagnoses and prescriptions of the physician(s?) A pool is certainly a conducive environment for a number of strengthening/flexibility exercises. Just work within the guidelines prescribed by the attending physician.