From age 14 to 25, I was convinced that heavy deadlifts would break my spine in half. After all, it seems legit.
But my view was molded by user error. Or as I like to say, "deadlifts don't hurt your back. What you're doing will hurt your back."
Deadlifts look as simple as picking it up and putting it down. However, it's one of the most nuanced and technical exercises out there. While I field a ton of questions about the deadlift everyday, one I hear most often is:
How much can - or should - your lower back round during a deadlift?
The answer is simple - not much at all. But that does need to be qualified with my usual "it depends."
Depends on what? It depends on why you're deadlifting.
1. If your goal is to move better, feel better, and get stronger...
You're going to want to avoid rounding or "tucking" on a deadlift. Straight spines are happy spines, and loading spinal flexion is one of the quickest ways to guarantee a visit to a spine specialist.
However, everyone's spine is going to look somewhat different. If someone has very little muscle definition in their lower back erectors, they may have a straighter or even a larger lordotic (natural) curve when they deadlift. If someone has a pair of ham steaks back there - like yours truly - what looks like spinal flexion may simply be their own version of neutral.
When in doubt, aim to be as straight as possible.
2. If your goal is to deadlift as much weight as possible...
We still want your back to stay straight, but realize that it's probably going to round at some point. Most people will never be in this category, because many never want to deadlift more than double their bodyweight. And that's OK!
As I wrote here, there's a few things I learned in my quest to deadlift 500 pounds (besides just learning much my writing has improved!). One of them being that when the bar gets heavy enough, your back is going to round. In rounding, your body is making itself more efficient. You shorten your body's levers enabling yourself to lift more weight.
Experience is also a big factor, as experienced lifters have earned some wiggle room in their technique. Many of the greatest deadlifters have a rounded back as they deadlift, but the degree of rounding doesn't change throughout the lift. They can "lock" their spine in place, something that beginners aren't able to do.
So again, how much rounding is appropriate? I like to think of it as a spectrum:
If someone has a slight round in their lower back but they're an experienced deadlifter, I'm not that worried about it. If someone resembles Quasimodo and they're struggling to deadlift two times their bodyweight? It's time to put aside the ego, before your spine does it for you.