Injury risk adds up quicker than you think

Posted on May 13, 2019

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(Last Updated On: May 13, 2019)

For any deadlift session, what’s the chance you blow your back out?

Something hard to know is the injury risk of any given exercise.

Even harder is knowing the injury risk of a given exercise for a given person.

The most well known injured area is the lower back.

One of the most well known exercises is the deadlift, which works the lower back.

This is where we can get awfully bogged down in uncalled for details.

“This study says…”

“But that study says…”

“Biomechanics says…”

“It depends on your individual structure…”

“I know a guy…”

Exercise science research is rarely great in this domain. You won’t find many prospective, randomized, large sample size, longterm, everyday people used as subjects, studies. I mean, good luck finding two studies that define injury the same way.

And even if it were great, it’s not going to tell you the risk of an individual. It’ll only give you an average. Not terribly helpful.

Thankfully, we don’t need to go that route.

To start, use the smallest, simplest number: 1%.

That is, for any deadlift session, there is a 99% chance you’ll be fine. Say, there’s a 99% chance your form doesn’t break down. That’s pretty damn good, right?

Over two sessions then, the probability your back will be fine is,

.99 * .99 = 98%

So, the probability you get hurt is,

1 – (.99^2) = 2%

Let’s say this deadlifter has two sessions per week. They take some time off through the year. Call it 50 weeks per year at 2 sessions per week = 100 deadlift sessions per year.

What’s the risk they blow their back out?

1 – (.99^100) = 63% (!!!)

Who wants to take odds worse than a coin flip they’ll seriously hurt their back this year?

-> For those who want the background on probability math. By the way, don’t feel bad if this is not intuitive. Probability is notoriously a mind twister, even for those with a math background (me included!).

And in two years,

1 – (.99^200) = 87%

If we were giving out grades, we went from having an exercise with a near perfect score for not getting hurt to an exercise with almost an A for causing injury.

Now let’s say we can pick an exercise with half the risk of deadlifting. Let’s merely use a single leg deadlift (commonly known as the single leg RDL). Where we more or less halve the weight of a regular deadlift.

-> Risk is not always this straight forward. I’ve had some clients where, as long as you weren’t high, you could easily see any single leg exercise was riskier than any double leg exercise, never mind how much weight was involved, because the person’s balance was so bad (you don’t toy with falling / broken hip risk).

For this post, I’m taking numerous similar liberties.

Our risk of back injury goes from 1% to 0.5% i.e. there is a 99.5% chance we’re fine.

1 – (.995^100) = 39%

Better than a coin flip we’re fine, but not exactly confidence inspiring!

-> Note we did not halve our longterm risk. This is the nature of compounding. A more critical point in a minute.

How about an exercise with a tenth of the regular deadlift risk? Maybe a simple back extension machine.

An exercise I’m not sure I’ve even heard of a person getting seriously hurt doing, and there’s not much I haven’t seen people screw up in a gym. I’ve seen people fall off a stationary bike! (Or say we do the back extension with a tenth of the weight you can deadlift, if that pleases you.)

1 – (.999^100) = 10%

A hell of a lot better, but if you’re a personal trainer who has 10 clients, and 10% i.e. one of them get seriously hurt, yearly…that’s not great.

We have all kinds of rationalizations for lifting a random piece of metal a certain way. Because it’s cool looking. Because cavemen had to do something similar. Because it works a ton of muscles at once. Too few of us ask,

“What’s the downside potential of this exercise?”

Which should be our starting point. 

Our number one rationalization for doing an exercise should be “because it provides my goal(s) for the least amount of risk.”

-> I have no qualms with doing something because it’s cool. Deadlifting IS cool. I have issue with justifying deadlifting (or whatever exercise) with dehydrated hallucinations.

Skydiving is also cool, but we don’t justify the rapid heartbeat it brings with “bro, great cardio!”

Use whatever numbers you want. Use them over many years. Which is how long we want people to exercise, right?

Look at 10 years of deadlifting vs a back extension machine.

1 – (.99^1000) = 99.99%

1 – (.999^1000) = 63%

Big ass difference. One is basically a guarantee while the other you’re not far from the coin flip. Not even a one percent difference over one session is a ~40% difference over ten years.

Use ANY number less than 99.5% over 10 years, and it comes out to a guarantee of injury. But use a number greater than 99.9, like 99.99, and,

1 – (.9999^1000) = 10%

10% chance of getting hurt after training consistently for 10 years? We always want better, but shit does happen when you move your body.

Are we training people with near certainty the exercises we give will not cause significant injury? We’re talking as close to 100% as possible. 99% confidence for any given session ain’t good enough. A 1% chance you get hurt today is a ~100% chance you get hurt in the not-too-distant future. Not ten years, but four and half years:

1 – (.99^450) = 99%

And this is for one exercise, for one body part. Not a full program of exercises, for the entire body.

The fact is there are certain exercises you can never have great certainty with, yet we’re intent on doing them. Why?

Again, do not get hung up on the exact numbers here. You don’t know the exact number(s), nor do I. The point is the safety of an exercise should scream out at you.

How much safer is a sumo deadlift than a conventional deadlift? That’s hard. You can try to figure it out, or throw it in the Too Hard pile and move on to something else.

But the difference between a back extension and a deadlift? That does not need to be meticulously researched or heavily thought about.  It’s smack you in the face obvious which one is more likely to hurt your back. Like humans have a pretty damn good sense of when one way of moving is considerably more dangerous than another. It’s why we’re alive.

A back extension exercise makes you wonder if it’s even possible to seriously to hurt your back. Those are the kinds of exercises we want to be doing.

-> In fact, I have many clients I just have them hold the back extension position. I don’t even have them do reps, so the technique is that easy. Isometrics are wonderful in this regard. It’s hard to screw up a movement if you don’t move!

-> I have many clients who want to deadlift. I’m more often than not all for it. But it’s not like we’re thinking “this is the safest and best thing for their back.”

What I don’t do is take a client who doesn’t care about deadlifting and force them to do it.

Here’s another one: a back squat vs a goblet squat.

You could go into a laboratory and take two years to get an eyes-roll-in-the-back-your-head research paper, or you could do the following in your head in 10 seconds:

  • A goblet squat is way more comfortable
  • A back squat involves setting up ***safety*** pins, the recommendation of a spotter, chance you have to dump the bar, etc.
  • Few can even do a goblet squat with more than 60 lbs, because their arms tire out before anything else does

Where it’s easy to figure how a person could seriously hurt themselves back squatting, you have to stretch your mind to imagine how a person could seriously hurt themselves doing a goblet squat.

Even better, make it a goblet box squat so the person can’t screw up how low they go:

You have a person who isn’t the most coordinated? Use no weight and have them hold something, like a power rack, so they can’t lose their balance.

You’re still nervous about their form? Even better- have them do a wall squat:


Now you REALLY have to think hard to come up with a way a person could mess that up.

You don’t know exactly how much safer it is, but you know one is way safer than another. You know a little difference in certainty today is a big difference in certainty tomorrow.

If you have clients who don’t care about ever lifting more than 60 lbs (most people), why bother trying to do a world class jump over a 7 foot hurdle (getting a regular person to back squat with solid form) when there’s a 1 foot bar you can step over (goblet box squat)? If you have a client who merely says “I want my legs to be stronger,” why start in graduate school when you can start in preschool?

If you at all believe the Hippocratic oath applies to anybody working with anybody else’s body, if you at all believe in thinking even just moderately longterm, you have to ask yourself, have we been exerting this level of caution?

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