I would say that if this is something you'd really like to do you might not want to let your back stop you but read further for details. If this something you're thinking of doing to help your back (but you're really not that interested in), I'd say, maybe not the best of activities. Of course you need to work with your doctor and understand your limitations before doing anything...that being said...
These are my own opinions and experiences but as someone who has been through the herniated disk experience where the pain was so bad I literally could not sit up or walk until after I had surgery and when, after surgery, I felt like a major league baseball player had hit me in the back with a bat and that pain felt like a relief compared to what I experienced before surgery I think I can offer a few thoughts.
From my own experience I think it really depends on where you take karate and the attitude of the sensei and students. When I began our senseis were in their 60s and had their share of health problems as many people their age do so they really understood what it meant not to be able to do something. This was a concern for me before I had a herniated disk because I was a woman "of a certain age" and went in to learn a martial art, to study something that took both mental and physical concentration, not to become a warrior, and not to get hurt.
I was about 2 years into karate when I had a herniated disk that required surgery and I was slow to recover both physically and mentally -- please note, I do believe this had nothing to do with karate. When I began studying again I was very clear with the senseis about what I felt comfortable doing and what I did not feel comfortable doing and they were perfectly fine with this and encouraged me to modify or do something else if I did not feel comfortable with the current activity.
As the years have passed since the surgery I've felt more comfortable working harder and adding in more moves but when something just seems too risky I just don't do it and work with the (now new) sensei to come up with an alternative. Falls are especially scary and we have modified requirements at belt levels to accommodate this.
My general thoughts about this are:
- From my own experience I feel better when I do karate (as long as I am careful). I think there is something about the more free form type of movement as opposed to an exercise bike or elliptical which is so, so steady.
- Everyone has some sort of limitation - whether they recognize it or
not. People favor one side over the other, are too focused, not
focused enough, don't have enough endurance, don't have quick
reflexes. People (at least in my experience) don't stop because of these limitations. Having problems with your back is another of these
limitations that you have to learn to deal with in your life. After
something as devastating as a herniated disk one is grateful to just
be walking pain free again so being able to do any moves is
life-affirming and leaving out a few is really no big deal.
- I think karate is about the journey and about being the best you can be and
really coming to terms with this. Where I study we all have jobs and
families and studies. We are not soldiers. We are pushing ourselves
and helping each other and traveling along this path. For me, the
benefits outweigh the risks and I'm very careful to keep it that
way.
- I think the coming to terms mentally with your vision for yourself and the reality of your physical situation is very powerful and allows you to embrace your humanity and empathy towards others.