Which exercise if you have bad knee(s)?

My husband has a TKR and was told to do stationary bike for exercise. He also walks daily. A friend with a TKR does elliptical and pool running. She also runs, but uses the other exercise to improve her fitness for long races.

@sijomial hit all the right stuff. Let me add some words of hope. I'm a codger-runner, and I get all sorts of aches and pains, having started only a few years back. I had to work up to jogging very slowly. First, I used the C25K app, repeating the easy workouts many times.

The Run-Walk-Run approach (which describes C25K and is also the name of a very popular book by Jeff Galloway) is very effective. You never need to progress any further toward running than your body can tolerate. In fact, you can do as @bakrueger61 says and just walk. It's all good!

The science of the knee has really progressed lately, and there is a lot you can do to make yours stronger. If you take the time to train properly, carefully, and consistently you may be able to adapt to a higher level of stress on them, even some jogging. Even online sessions with a PT could be helpful.

Best of luck and keep exercising!

Great advice above. Just to add to it, when I was losing my weight, I went to a spinning class and pushed it too hard. My wife and I went to movie that night and she literally had to help me to the car. I could barely walk. As a man, I was embarrassed that my 150 lb wife had to practically put me on her arm and lift half of my body to the car.

Seven years later, I row 50 miles a week and lift 2X a week. The spinning classes would be "light" work for me now.

Work on losing the weight, see a doc if it's a sharp or unidentifiable pain and just move as best as you can. Tai Chi is a great way to start with sore knees and joints. It works on both fitness, balance and flexibility. With pools closed, it's a fantastic alternative to water aerobics. YouTube has a lot of Tai Chi beginner workouts.

I'm another one in the "it matters what's wrong with your knee" camp. Diagnosis, and ideally follow up physical therapy, are really useful.

With some knee problems, you can do things that hurt to the point you can tolerate, and not make the problems worse (they might even get better, depending). With other knee problems, you can very much make them worse by doing the wrong things, even burn bridges. (My rowing double partner and I both have "bad knees". The same orthopedist gave each of us completely different treatments and follow-up recommendations, because we had very different knee conditions.)

I have arthritis in both knees, and a torn meniscus in at least one (I suspect both now, but only one was imaged at the time). Quad strength is not a problem (confirmed by orthopedist and physical therapist). From physical therapy and experimentation (among other things), I've learned that with my particular conditions in the particular part(s) of the knees that are affected, I can do pretty intense straight-line hinging movements of my knees with minimal penalty, but that impact or torque (like turning on a weighted leg) will cause further degradation, sometimes very quickly. My desire is to defer surgery (which my orthopedist says is sometime in my future) as long as possible, as long as I can have a happy life meantime.

I can row (on-water and machine), bike, and spin. Despite Mike being correct that Tai Chi is great for some kinds of knee issues (there's even a "Tai Chi for arthritis" branch of it), it's a no-go for me because of the "weighted turn" issue (previously, I had studied it fairly diligently, with multiple real life teachers, for around 8 years at one point - my late husband was also a Tai Chi teacher). I can swim, though some kicks are more stressful than others. I can't do things like running, aerobic dance, leapy-jumpy exercise, or run-and-turn games like tennis or basketball . . . unless I want to head toward surgery faster.

FWIW, getting to a healthy weight made a huge reduction in my routine pain/discomfort levels and frequency, so if you aren't there yet, that would be a good plan, and that can be achieved pretty much entirely on the eating side of things.

If you're unable to see an orthopedist during shelter-at-home orders, some cautious experimentation with different exercise forms (with plenty of rest/recovery between, at first) are probably your best bet. Don't forget to use things like ice, heat, stretching, etc., according to the standard prescriptive rules, as part of recovery.

I'm 56 and my knees bother me too. I do low impact workouts, weight workouts and yoga etc from youtube. Here is a page full: https://www.youtube.com/results?search_query=easy+on+the+knees+workout

That is one thing that sucks about getting older - painful knees & joints.