"I wasn't even doing anything hard!"
I hear it over and over again. Someone hobbles into my office with a blown up lower back, and has no idea why they're in the situation they are. Whether it's lifting the toilet seat, reaching for a banana, or just tying your shoes, the potential for a low back injury is always there.
Without the support of the erector spinae and our core muscles, our lumbar spine is severely lacking in stability. Moving a joint to its full end range puts stress on the surrounding ligaments. Maintaining that stress over time can cause elongation of those ligaments which will lead to instability at the joint. In a region that is so dependent on leverage, such as the lumbar spine, this can be catastrophic. For anybody who has experienced a bulged disc or severe muscle spasm, you know what I'm talking about.
It comes down to this: no matter how benign the activity, engagement of our core muscles (including our lumbar erectors) is ABSOLUTELY ESSENTIAL. I was really pleased to see this video showing the mechanism of injury, and it's prevention so plainly. Later, I'll share some resources that will help with the proper activation of your core but for now, do your best to maintain a neutral spine when moving around.