Yeah, I’ve had an L5-S1 discectomy and, due to the extreme herniation, an L5-S1 fusion. The most important thing to remember is your patience and consistency. No big jumps in weight, and doing less this week with the confidence that you can do it again next week is better than doing more but being uncertain how the next week will shape up.
To address “force down my spinal column”: any weight you support above the waist is loading your spinal column. If you’re holding a kettlebell in your hands, it doesn’t matter if you’re holding it below your waist, the force is transferred up your arms, to your shoulders, down your spine, and then to your legs. You need stronger muscles in your back to support and stabilize the spine, but you need that whether you’re carrying groceries, picking up a child, bending over to pet a dog, or squatting a barbell. But squatting a barbell gives you a lot of opportunities for controlled, steady progressive overload to build the muscles instead of further herniating the discs.
All that said… after my fusion was solid (6-8 months post-op), I spent another year where my primary and most strenuous exercise was doing yoga 1-2x a week. Maybe a yoga class is a good avenue for you, maybe something else is, but regular consistent work on balance, stability, and body weight resistance isn’t a bad way to spend some time. You can build pretty impressive strength that way, working through progressively harder variations.
I didn’t do that. I eventually started going to the gym, and worked with a physiotherapist on form. Over the next couple of years I learned that if I always lift only in the winter, I’ll always start the next winter at pretty much the same place, and I’ll always finish the off season at the same place, and I won’t really progress year over year. Lifting through the racing season this year, I’m finally breaking plateaus (albeit slowly, because patience is key!). So I’d recommend doing that, but be mindful of your volume, don’t get greedy, and just be confident that even holding on to strength gains while going hard on the bike is an accomplishment.
I agree with @RONDAL on his points. I don’t ever need to find out what my 1RM, 3RM, or 5RM is. I can estimate them, but even at 5 reps I always want to feel like I’m at 90-95% of what I could do. That’s plenty hard, it triggers supercompensation and strength gains, it’s enough for hypertrophy, and I never feel like I need to deviate from excellent, back-protecting form to get the weight up.