Well this is timely content for me. I am 32, healthy weight range, and going to have athroplasty next week to replace L5/S1 disc. Information I was told is 9/10 have positive outcome with 1/10 still experiencing pain post recovery.
You could do this with a lengthy, complicated series of midsection/trunk exercises, or you could hit every associated muscle in the correct balance and proportion by walking.
Your body was built to walk - you are a walking machine.
I had a blown L4/L5 going into basic training and was immediately walking 5-8 miles per day. It was very painful and debilitating for the first week ... and then it was gone. I believe the muscle action pulls the spine back into proper alignment and gives the disc nowhere else to go but where it belongs.[1]
If you look, you will find this to be a very common anecdote.
[1] IANAD and obviously cannot speak to severe trauma, fractures, etc.
This is not advice you should be giving.
You are not his doctor. You don't know the extent or type of his injuries. You have no idea if core workouts will help. You have no idea if he/she even can walk.
90% of herniated discs resolve in 3 months. For the 10% that don't sometimes surgical intervention is needed. Don't muddy the water with vague uninformed advice if you don't know this persons exact medical details.
On one hand I agree, but it is useful advice to say make sure to talk to different doctors. If someone goes to a surgeon, they are likely to lean towards surgery. I'm going to assume the GP has already seen doctors that specialize in non-surgical treatments like steroid injections directly at the site, but for anyone else reading this information could be useful.
And, the OP is right. The doctors I've talked to have all said surgery needs to be the absolute last resort. Many end up worse off or needing more surgery.
I was 25 when I had surgery though, so god only knows what kind of shit I'll be in when I'm 45. Hoping those stem cell treatments take off.
At least for me it's certainly some muscle thing as once winter comes (and I'm walking less) the back problems come back. One of the best things this winter was getting a job in an large sprawling office, which means I'm walking several miles every day at work (all indoors). Haven't had any issues this winter at all.
Again, I think a good mental model is that of a corset, or a brace. In this case, the corset you are donning is made of your own muscle.
You could attempt to build that own-muscle corset section by section by doing all of the 40 different trunk and midsection rehab exercises, but even then, in what balance or proportion could you hope to execute them ?
Instead, you can hit all of them, in concert, and in appropriate proportions, by walking.
The difficult part is that bad back pain will not make for easy, pain-free walking - at least at first. I found 4-6 mile walks to produce a fair amount of back pain in the year immediately following my initial disc herniation/tear. It took that forced week or so at the beginning of basic training to pull my spine back together.