I seldom visit this forum but the title of this thread interested me, so here I am and I read the whole article. I agree with most of it and thus disagree with some of it.
I'm 75 and started riding again at 50. I've been doing strength work in the gym for over 20 of those years, mostly heavy work to near failure. Mostly but not all. I never work my back to near failure, though I have worked it hard. I have the usual older person's spine, spinal stenosis, thin disks, arthritic facets. This is normal. What's not normal is that I can still do what I do, ride hard for long distances and lift heavy. So that's my experience.
I do not strength train for the hours that a track cyclist does, especially sprinters. I'm an endurance road rider. This past summer, I had an episode of sciatica on my right side. It was excruciating as is normal, to the point that I could hardly walk The why of the sciatica was that I had a really bad saddle sore, which was misdiagnosed and maltreated, to the extent that while thie treatment happened in May, I'm still fighting it. This injury took me off my bike for months. The bicycle is, besides being the best machine ever invented for extracting energy from the human body, the best back exercise there is. A big THAT IS, if you bend your lower back right at the top of your shorts and then keep it as straight as possible all the way to your neck. The guys in the top photo are like "oh my god, do not do that!" When one squats or deadlifts, a helper should be able to put a straight edge on your back and have it touch your lumbar spine, all the way up your back and the back of your head. It's important to hold your spine in column when under load.
That said, I disagree about spinal flexion and stretching. Google for the McKenzie Method. After I contracted the dreaded sciatica, I started doing McKenzie stretches, various rotating stretches (google sciatica stretches), all of which helped. What helped the most was walking with an exaggerated rolling pelvic motion. The hurt like the very devil for the first mile, but then got better. I no longer have any sciatic pain or sore or tight back muscles. Why? Because I'm back on my bike 5 or so days/week. I'm again strength training and stretching. And also still doing a little walking.
What have I learned? I've learned that high rep mild strain is the best thing for spine health, i.e. bike riding with a straight back using a position and pedal stroke which engages the entire posterior chain, all the way to the shoulder blades. This has to be coupled with the ability to bend the back without pushing any tendon or muscle into the high strain area, which of course means you have to stretch to avoid same. I don't mean extreme stretching, just able to put your knuckles on the floor barefoot. Your spine likes movement. It likes to be loose and yet has to have the muscular strength to hold it in column when under load. It's not any one thing and it's complicated.
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