Why does my back hurt so much when I walk on the treadmill but not when I do step aerobics, kickboxing, etc? I have a herniated lumbar disc and ever since my diagnosis I've had problems walking more than a mile on the treadmill. Any longer and I get back spasms. I thought walking was supposed to be great for people with back problems and stepping the worst, but in my case it seems to be the opposite. Of course, I find walking extremely boring so there probably would be no love lost there if I had to avoid this exercise, but some days I just want a low impact workout and walking fits the bill. Anyone else notice this? I haven't been to my ortho for months because my back pain isn't bad enough to warrant any drastic interventions.