The lower back muscles - those bands either side of the spine, get plenty of exercise just paddling a surfboard around the place. Are you saying you get "good" DOMS in your lower back muscles, or are you getting bad back ache in your lower back? If it is the latter then you have already been down the path of making it worse with barbell lifting. However, you are already doing heaps of general core strength planking stuff I believe, so maybe time to go back to the physio for a follow up and recommendations.
What is your general core stability like? e.g. can you balance on one foot, pick up a shoe off the ground, put the shoe on your foot that is lifted off the ground and tie the shoe lace while remaining balanced on the other leg without wobbling around or toppling over? edit --> comes with my usual disclaimer, I don't know what I am talking about, but my core feels solid nowadays.
I
never get any DOMS in my back. I have soreness in my back all the time but not from exercise and very low grade. The barbell never made my back worse. Because of the DOMS (and lack of it in my back) I just have this impression that the back is not getting enough work.
I was doing barbell stuff (light- not Havoc and VM weight) twice a week. But I would have DOMS for 2-3 days afterwards only in hamstrings and glutes. I also did not feel any improvement in my surfing (back stability during pop ups) which is the only (main reason) I'm doing them. A friend told me it looked like I was popping up fast but that was on a mid length board. Whenever it was overhead and hollow and I tried riding my shortboard and it was not pretty.
I had replaced one barbell day with body weight day. I feel I need really dynamic stuff. Pushups, pull ups, planks, mountain climbers and especially burpees/pop ups. The burpees/pop ups still feel the worst. It's like in that second, in the air, as you go from extension to flexion, heaving with the shoulders, drawing in the legs, my spine is loose and subject to ....???
Any movement that requires pulling up my knee and bending over- putting on shoes, taking off the wetsuit, crouching for tubes, still hurts my back.
I'm wondering if I need to start doing some kind of back flexion stretches or exercises (VM is going to eviscerate me)....