I feel your pain...literally.
A few years back I was loading heavy boxes up into my truck and like an idiot did what you should not do, bend at the waist, lift and twist up over the side of the bed. I woke up in excruciating pain. I'd had a Chiropractor for years due to a mid back issue after a motorcycle crash injury years ago and he diagnosed me as having "bulging discs" and put me on an expensive daily treatment plan (my insurance doesn't cover Chiropractors) After a couple of weeks under his "plan", I ended up in the ER. An MRI showed I'd actually herniated L4/L5 and L5/S1. Same deal. Excruciating pain down my left buttock and the outside edge of my leg from my knee down through my left foot is numb and remains numb to this day.
They put me on high dose steroids for a week for the inflammation and I also went to Carolina Neurosurgery and Spine and worked with a Physiatrist there (Dr. Vemuri). Same deal. Spinal shot, avoid surgery if at all possible and continue with PT and core strengthening exercises.
While I will likely never be a runner or tennis player again due to the residual numbness, I have to say that my back never feels looser and more normal than when I come out of the trails. I do not do the jumps anymore due to the compression they place on the spine when you land, but other than that, riding has not caused me any issues. Usually when I do have back issues now, it happens doing something as simple as pulling on boots! I worked on Saturday hoeing out a bunch of clogged drains at Sherman and paid the price on Sunday with lower back soreness, although an Alleve seemed to make everything feel pretty ok. It's a bit better today.
I have resigned myself to the numbness being permanent, and even on my best days, I can still tell that my lower back is something less than 100% and always will be. It's tight, it's always a bit sore, but tolerable. I try to stay up with the exercises like the one where you do kind of a pushup, but keep your waistline pressed to the floor, but the better I feel the more I slack off in doing them. Because of my Chiropractor's misdiagnosis, I will never see one again.
I also ride with a lumbar support belt which really helps keep everything from slopping around in my lower back and would never ride without one now. I have the Sport Belt (
(You need to Login or Register to view media files and links) ) but they don't sell them anymore. Lots of other options on Amazon. It also gave me an excuse to upgrade from an entry level hardtail to a higher end full suspension MTB. I keep the rear set on squishy to allow maximum travel and minimal spine compression.
I get tempted at those constant TV commercials from the Laser Spine Institute which tout that they can solve all my problems. If you spend some time reading patient reviews however, the results are all over the board from "significant relief" to "much worse". So... I try to keep my core strong and I never pick anything up by bending at the waist. Seems to be the best I am going to get and a lifelong annoyance.
Good luck to you.