Exercising in space- when spinal DEcompression is a concern for lower back pain

Posted on February 3, 2016

(Last Updated On: May 20, 2017)

I think space is awesome. I think going to Mars is awesome. I think it’s important to do. I’m not going to make an argument why, but you can see one here.

A problem for human spaceflight is countering the negative impacts of moving in an environment where gravity is less than Earth’s. This is the predominant impetus for some space posts I’ll have, as there is a ton here which can be applied to everyday people on Earth, and vice versa.

Sometimes I’ll hit on current treatments; sometimes I’ll hit on ways I think things could potentially be improved. Maybe this can be my small way to help the Mars movement.

Finally, I want to stress, even if you’re not interested in space, I think this stuff can be valuable to learn about. This post has some application to taking care of the back early in the morning, lower back friendly exercise in general, and more specifics for those who have lower back issues when their back rounds (lumbar flexion).

Flexion is going forward; extension is going backward.

Flexion is going forward; extension is going backward.

When we wake up in the morning we’re almost a half inch taller than at the end of the day. Why? Our discs gain a bit of size throughout the night. Thus, when waking, the discs are a little more full, and we’re a little bit taller.

Spinal discs.

Spinal bones with discs in between.

Over the course of the day, as we compress our spine, we get shorter. Over many people’s lifetime, the compressive forces of the day outweigh the compressive forces of the night. As we get older, many get shorter.

Why do our discs do this? When the discs are vertically compressed they 1) Are having water squeezed out of them and 2) The compression causes the disc to have less room. Take away this compression, like when laying down, and suddenly the discs have some room to breathe, meaning water can now get back into the disc. (A form of osmosis.)

Think of it like a sponge. Squeeze a sponge in a bucket of water, and the sponge (disc) gets smaller.Sponge water tank GIF 2

Let go of the sponge -lay horizontally- and the sponge gets filled back up with water.

Sponge tank water back in GIF 2

If you’re in space and weightless, you don’t have the compressive forces of gravity throughout the day. Rather than grow a bit at night, shrink a bit during the day, you instead grow a bit, grow a little more, and stay that way. Astronauts are up to *three* inches taller in space than on Earth.

This in itself can cause discomfort and or pain. Just as a spine can be too compressed, it can be too decompressed. The body constantly finds itself falling into intervals. Sleep for 8 hours, wake for 16. Repeat. Breathe in every couple seconds, breathe out every couple seconds. When these intervals get disrupted, things happen. Breathe in for two seconds, breathe out five minutes later? Probably dead. Sleep 4 hours, wake for 20? Hate the world and have a more than usual compressed spine. Lay down for 24 hours straight? Have a more than usual decompressed spine.

Before bed rest for an extended period of time on left; after on right.

Spine discs before and after bed rest

Notice the fuller discs, and subsequently longer spine, on the right.

What some astronauts will do to alleviate this is stand in a section of the spacecraft where their feet are sturdy, hands are above the head but touching a “ceiling,” then push their feet and hands into the spacecraft (in opposite directions) in order to compress their spine. (I thought there was a picture of an astronaut doing this somewhere, but I can’t find one.)

Disc height / filledness has significant implications for exercise recommendations

The noteworthy spinal researcher Stuart McGill has talked about this spinal elongation phenomenon and the implications it has for training early in the morning. You don’t want to be loading an excessively filled disc. You especially don’t want to be loading the spine in flexion. With all that extra fluid in there, a posterior herniation -disc gets squished enough in the front that part of the disc protrudes out the back of the spine- is more likely.

spinal disc protrusion lower back herniation

Posterior disc herniation.

“Adams and colleagues estimated that disc-bending stresses were increased by 300% and ligament stresses by 80% in the morning compared to the evening; they concluded that there is an increased risk of injury to these tissues during bending forward early in the morning. Recently, Snook and colleagues (1998) demonstrated that simply avoiding full lumbar flexion in the morning reduced back symptoms.”

From Stuart McGill’s Low Back Disorders Second Edition.

A common analogy for this is a credit card. Take a card, bend it one way over and over, and eventually it snaps, or herniates. The spine doesn’t quite snap like that, it’s more like stuff oozes out, but you get the idea. Next, take a longer credit card. Or think the difference between snapping a short versus long pencil. The longer one is easier to break.

-> This is one reason as we age it’s less and less common to see acute lower back disc issues. It’s usually younger people; typically male. (Degeneration can certainly be part of the problem for geriatrics though.) They have more of a disc left to herniate. (More stuff which can ooze out.) This is also why younger people are more prone to flexion issues (their spine is longer), while older people rarely have flexion issues. Extension will be their problem, as will more chronic issues, such as stenosis. As the spine becomes more compressed with age, there isn’t as much room for the nerves. They’re more likely to be pinched.

Another aspect to all this is when the spine is elongated, the ligaments become more tensioned.

anterior and posterior longitudinal ligament

Elongate the spine => stretch the ligaments.

Because of this, flexion range of motion is reduced after bed rest. If we were to engage in spinal flexion, not only do we have discs more susceptible to herniating, we have tissues which are already at their / closer to their terminal range of motion. We can’t flex as much because the anatomy doesn’t have as much to give, nor can it help as much to resist whatever flexion we do.

We have a confluence of injury risk factors increased at the same time.

-> Some have difficulty bending over when waking up in the morning. That’s not always stiffness, in the sense of you need to get some blood flowing after not moving for a while. It’s your discs, and subsequently some tissues, need to get compressed.

On Earth, no big deal. Don’t lift heavy stuff early in the morning. If you do, then be sure it doesn’t involve bending the spine. (Being groggy and slow moving in the morning has some value!) Waiting an hour is probably sufficient before heavy resistance training. If you just want to go for a walk, then it doesn’t matter regardless. Also, if you have a lower back history, you might want to be careful picking up the baby or leaning over for the dog first thing in the morning. That spine won’t love bending for a little while.

In space, where we aren’t going to get that compression, when I see an astronaut performing sit-ups, or squatting with form like this, I get very nervous:

Astronaut Squatting

For an astronaut, complete avoidance of spinal flexion is probably best. Health is paramount once you get in space. You can’t take a couple weeks off. Do that and muscular strength can decrease by 10%, bone density can decrease by half a percent (after a couple weeks!). It’s a battle to keep these things at bay, and injured tissue significantly hampers that battle.

Exercises to be careful with, or avoid

Things like squatting and deadlifting don’t necessitate spinal flexion. However, when you’re doing these heavily, spinal flexion becomes progressively likely. All it takes is one rep for the back to need a month off. It’s tough to have perfect form, and the heavier you go, the more true this is. Hence all the people who’ve destroyed their backs while deadlifting.

At a lower back pain conference I got to see, meet and speak with, Julie Hides. Julie does research on astronauts, and has done some of the bed rest work on Earth, where they try to simulate weightlessness for space application.

One thing she discussed was research that the multifidus muscle, a back muscle which extends the  lower back -or prevents flexion, depending how you want to think about this- selectively atrophies when the gravitational force the spine has to deal with is significantly lowered. (Astronauts and bed rest people exhibit this.)

Furthermore (Julie and I didn’t discuss this part), because the spine is elongated, when you put a bar on your back, the multifidus now has a longer lever arm it has to generate force over. Anyone who has squatted with the bar at the top of their neck versus lower, “the shelf,” knows how much one to a few inches can matter here. A significant reduction in how much weight the person can lift happens with the higher bar placement. This is why no powerlifter has a high bar set up.

Credit: http://functionalalexch.blogspot.com/2013/02/low-bar-vs-high-bar-back-squat.html

High bar left; low bar right. Notice high bar means bar is further away from lower back, causing an increase in lever arm length. The further away, the harder the lift. Credit: http://functionalalexch.blogspot.com/2013/02/low-bar-vs-high-bar-back-squat.html

Large human with a lot of weight...using bands.

Notice the bar lower. Powerlifters compete to lift the most weight. Inches matter.

A longer lever arm, a longer spine, causes the muscle to be stretched out. Muscles have a sweet spot in which they can generate force. If they’re too contracted, the filaments can’t hook on to anything. Too stretched, and the filaments can’t hook anything either.

GIF made from this cool video: http://www.youtube.com/watch?v=0kFmbrRJq4w

If the pink (it’s salmon colored!) moves too far away or too close to the blue, it has nothing left to grab on to. (GIF made from this cool video: http://www.youtube.com/watch?v=0kFmbrRJq4w )

Filament 5

Fully contracted. Nothing more to hook on to.

While we may not necessarily approach the multifidus’ terminal range of motion, we end up training it to get good at contracting with the spine in a position of flexion. As the spine elongates in space, the lower back has to flex some i.e. by the lumbar spine straightening out its curve, it ends up flexing. (If that statement is confusing, don’t worry, we’ll come back to this.)

Therefore, we adapt the muscle to preferentially contract in a position of flexion, likely causing maladaption in the ability to contract to get and or keep us out of flexion. It gets better contracting at a longer length -things are flexed- meaning it gets worse contracting at a shorter length.

-> This may be the easiest way to think of all this: If we’re already doing a certain movement, like flexing our back, a ton, 1) we get good at that movement 2) we’re unlikely to need more of it. After a night of sleep, (other than particular sleep positions) we just flexed our back for ~8 hours. When we wake up, the first things we do probably shouldn’t involve more flexion. And when we first wake up, it’s going to be harder to avoid flexing the back, like when squatting.

In space, we’re flexing our back every hour of the day. We don’t need more of it when it comes to our exercise. And it gets harder to prevent flexing the back. This astronaut is a well trained lifter. He played division I football. He’s been squatting for probably 25 years, if not more. In other videos, like on Earth, he has solid form. It’s more likely he’s trying to, but just can’t, prevent this, than him practicing bad technique:

Astronaut Squatting With Rounded Line


  • Hypertrophied discs are more likely to herniate
  • Spinal ligaments approach their maximal range of motion as decompression increases
  • Multifidus selectively atrophies in weightlessness environments
  • Multifidus, as well as other spinal erectors, have a longer lever arm to deal with when the spine is decompressed
  • Being at terminal range of motion decreases a tissue’s ability to contract / spinal erectors become trained at being in flexion, causing them to have a harder time dealing with generating extension

Not only are our astronauts more likely to get injured during spinal flexion, they are more likely to have issues preventing spinal flexion. 

Furthermore, astronauts are often in their 40s and 50s. They are more likely to get injured, period.

Certain populations don’t fit certain exercises. It’s not always a matter of proper coaching or better technique training. Sometimes it’s a matter of “this exercise doesn’t work for this person.” And you move on.

If I’m an astronaut, or helping train astronauts, deadlifting isn’t worth the reward. One rep can ruin a mission. Sure, other exercises can say that, but they are few and far between; throwing your back out is worse than hurting your shoulder (on Earth and in space- astronauts primarily have issues with bone density in the lower body; not the upper (not being able to train the upper body isn’t as big of a deal)), and no other exercise has the graveyard of lower backs that deadlifting does.

I’d also avoid sit-ups, with their significant spinal flexion:

And no, even if you do your best to be more upright, it’s not going to happen on this exercise. This:

Sit up more upright

Still consists of a flexed lumbar spine. Neutral for the lumbar spine means a bit of a curve. Meaning if the lumbar spine is flat, it has then gone into flexion.

The spinal flexion element isn’t the only concern. Sit ups significantly work the abdominals and hip flexors, namely the psoas. That is, sit ups significantly work the trunk flexors. The trunk flexors, in bed rest and microgravity, tend to either remain the same size, or hypertrophy! (Psoas doesn’t change after exposure to microgravity.) Performing hundreds of reps of sit ups, like they’re commonly done, could exacerbate this imbalance, and it seems musculature like the psoas is worked enough during spaceflight that it doesn’t need extra work.

This is not too dissimilar from everyday people on Earth. So many sit with their body rounded forward, which shortens the trunk flexors. (Abdominals in particular.)

Neck and upper back chest GIF FULl

As the shoulders round forward and chest caves, the abdominals, such as the rectus abdominus, is shortened.

abdominal muscles

Where the last thing a person then needs is more work or exercise of this type, where they’re pulling the shoulders to the knees. If anything, they usually need the opposite. Thoracic extension, not thoracic flexion.

The bike fits in here too. While astronauts have a different bike, most biking causes people to round their spine as they lean over on the handle bars.

If we persisted with biking, which we really don’t need to be bothering with in space, we need to be sure the spine stays more neutral. It can be done, but it’s tougher than say, just going on the treadmill for cardio.

It’s not only a muscular thing here; you don’t want to reinforce the pattern of spinal flexion.

-> Thoracic flexion isn’t so much the problem here as lumbar flexion is. As we discussed earlier, the lower back has a natural curve to it. When the spine stretches, it subsequently loses that curve, making it in a more flexed position. For the thoracic spine, it’s the opposite. Its natural curve goes the other way. So when it straightens out, it ends up being in a position of more extension, which is a good thing for most people nowadays. Even more so for an older population. (Some have half-seriously suggested in the future space tourism could be a way to get out of some lower back pain (decompression) and help those suffering from a hunchback posture i.e. go into space for a couple week vacation rather than Hawaii.)

Spine from right side. If elongated, each curve will diminish. Credit: http://www.spineuniverse.com/sites/default/files/legacy-images/spine2-BB.jpg

Spine from right side. If elongated, each curve will diminish. Credit: http://www.spineuniverse.com/sites/default/files/legacy-images/spine2-BB.jpg

Bike for 30-60 minutes a day, have a spine which is in flexion ~23 hours a day from microgravity, bend that spine even more during things like computer work, and we can see a potential problem here.

With squatting though, there are things to be done to make it friendlier. We can make all our exercises friendlier.

Warming up

NASA has the astronauts on different workout schedules. Someone might do their resistance training in the morning and cardiovascular work in the afternoon, where someone else might do the opposite. From what I’ve seen, this is due to limited resources, e.g. there is only one treadmill, than anything else.

From a training perspective, what you do first matters. Just like on Earth we’d prefer to walk around, be upright for a while, before lifting anything, why don’t we do the same thing in space? We get on the treadmill for 30-60 minutes before any resistance training.

We would want to insure during this walking we have some spinal extension going on. A mirror, or another astronaut, could provide some nice feedback here, to insure we’re not walking like Quasimodo.

We may be at the point a motion sensor could do this for the person as well. We have things currently where it can sense how hunched over you are. We could probably have sensors to assess how flexed your lower back is too.

-> Of course, if we’re only doing upper body that day, then we probably don’t need to bother with this. It certainly wouldn’t hurt, and would if anything be beneficial -there is some leaning over in some upper body exercises- but it’s not as important as when we do lower body / spine work.

Now to squatting. Before every set of squats, we can do our spinal compression maneuver. Where we’re pushing opposite ways with the hands and feet at the same time.

From reading various astronaut accounts, they seem to know when their spinal discs are too filled, because they’ll be in discomfort. With the spinal compression “warm-up,” the idea is if the astronaut’s back is in discomfort, it better get out of discomfort before heavy squatting.

The moment we stop our treadmill warm up, the moment we are setting up for our next squat set, those discs start filling up again. Spending 30 seconds, or however long is best, before each set, while the person is likely doing a rest break anyways, gives a nice insurance policy.

-> Again, you can’t lay up in bed for a couple weeks in space. Loaded movement is critical to maintaining bone health. We don’t want to do anything to jeopardize our ability to exercise, do a spacewalk, nor do we want to throw our back out a couple days before we land on Mars.

To help mobilize the spine into some extension, we can go into hills and valleys,

It’s common to lose some lumbar lordosis in microgravity. This helps us get that range of motion back each day, and before each squat. But we want to compress the spine first. It’s easier to move a slackened (compressed) rubber band than a tautened one. The order matters here.

I like to do “filler exercises” between heavier exercises. We could entertain something like this,

A) Treadmill warm up with spinal feedback ~45 minutes

B1) Spinal compression exercise 2 sets 30 seconds

B2) Hills and valleys 2 sets 15 reps

C1) Squat 4 sets of 10 reps

C2) Spinal compression exercise 4 sets of 30 seconds

C3) Upper body exercise X sets Y reps

C4) Hills and valleys 4 sets 12 reps

And continue from there.

Type of squat

Rather than a back squat we can move to a front squat. In a front squat there is more axial loading on the spine. Where a back squat invites sheer loading. In other words, you can more easily be upright in a front squat.

Front Squat on left:

I believe the original credit for this goes to Mark Rippetoe.

I believe the original credit for this goes to Mark Rippetoe.

Axial loading is friendlier to the spine. The back handles compression quite well, and plus we want that compression.

Furthermore, we’re unlikely to be able to lift the same weight in a front squat as we can in a back squat. This can be a good thing, as resistance means mass, and mass gets on a spaceship at a premium price. If we can generate a similar training effect with less resistance (single leg training being another worth looking into element), we should.

-> The main reason you lift less weight in a front squat is the lower back is minimized from helping. The legs get a similar training effect, but the lower back does not. We do want to train the lower back though, which we’ll get to in a minute.

Front squatting is also much, much friendlier to the shoulders. Many have trouble getting their elbows behind their shoulders like in a back squat. This is more true as age increases. (Astronauts are older; the shoulder is their most commonly injured area; we’ll talk more about shoulders in another post.)


While squatting, most have a point of depth where their spine will bend. A notable exception here are olympic weightlifters, who have a hip structure very few others have. Not everyone can do this:

deep squat good back

Though women can get away with this much more often than men.

Most can get to 90 degrees with no problem. Below that though, all bets are off. The hips can only flex so much, and it’s different for all people. Once they’ve hit their maximal flexion range of motion, in order to keep going down, something else has to bend. That something else is the spine. 91 degrees? Your low back may start rounding. (The “butt wink.”) For someone else, it might be 100, and others who can get even further.

Credit: http://www.leeboycetraining.com/assets/images/userPics/tinymce/buttwink1.png

Once past 90, the spine started bending. Credit: Lee Boyce.

We would want to know where this point is for every astronaut, as we don’t want them going below it. On Earth, you can usually get a feel for this just by watching someone bodyweight squat to different depths.

From there, we know the point, and we don’t go below that. For astronauts, we would probably want to stay a couple inches above that point, to really be cautious.

-> This is where front squatting is again more friendly. A back squat necessitates more hip flexion, due to the person inevitably getting pushed forward some. (Shoulders and hips come closer together.) In a front squat, because it’s easier to stay upright, the hips don’t have to flex as much. In a front squat, we can go a little lower while maintaining a neutral spine.

Notice shoulders and knees progressively closer together, as we go from left to right:

I believe the original credit for this goes to Mark Rippetoe.

Doing this by feel can be very hard. “I can only go down X amount of inches.” Knowing where X is without any feedback is tough. Because we usually want the exerciser thinking about another cue or two while squatting, we can have the squatting be done to a bench / predetermined height.

This way they don’t have to think about depth. They can focus on, in the astronaut case, making sure their spine doesn’t round over. Or perhaps something with their knees. Not having to think about depth frees the mind up for another cue. We only get one or two cues to think about. We need to choose carefully.

Bent over row

A good amount of astronauts do bent over rowing:

Many times a trainee will start jerking the bar up, in order to lift the weight. We can cue out of this, but this is another one of those risk-reward situations. There are other ways to get the same effects. (Even above, the spine could be better, as the lumbar area is a little flexed.)

The purpose of bent over rowing is to primarily work the upper back and biceps. The grip and lower back get worked, but that’s not usually the intention. Regardless, we can work all these muscles without having to be in a position our spines are vulnerable to.

If we use bands, which I’m a proponent of in space (saves mass), then we can do Face Pulls while keeping the spine from any potential flexion loading.

Face Pulls actually invite a little lower back extension. Notice the person above arching their back some. A good thing in an astronaut’s case

Biceps we can do good ol’ curls. (Biceps do get worked in a facepull as well.)

For the grip, we could hold the barbell without leaning over.

For the lower back…

Simulating the work an upright spine causes

While I would avoid deadlifting, I wouldn’t avoid spinal extension work. Something like this,

Thinking back to the multifidus atrophy from bed rest / not having to maintain an upright spine, in the case of knowing why this happened, what would we want to do to prevent it? Do the opposite, right? We took someone, had them lay down / not have to maintain an upright spine => instead we want them to have to maintain an upright spine.

Our spine doesn’t go through changes due to a lack of deadlifting. In the case of space travel, it goes through changes due to a lack of low load, sustained, work. That’s why I prefer the band good morning exercise, done for tons and tons of reps, all insuring the lower back is not flexing. This way we get that low load, sustained, more endurance oriented work. (We’re also getting some of this on the treadmill.)

While similar to the positioning in a bent over row, there are other things going on in a bent over row. Like working the arms. In the banded good morning, the focus is solely on lower back positioning. The focus isn’t on getting the upper body stronger.

Certain exercises cause certain people to take a certain mindset. Deadlifting tends to be one of these. “Oh we’re deadlifting today. LET’S GET TURNT UP.”

Baby Deadlift light weight

One of the things I talked with Julie Hides about was how the astronauts are not always amenable to their trainers recommendations. I had heard about this before, from an astronaut:

Clayton Anderson astronaut training 1

By moving to a band, it’s harder for the astronauts to overdo it. It sets the tone for the exercise. With a barbell in front of a person, being told to lift it, it sets a different, often much more intense -at a time we don’t want astronauts to be intense to their spine- tone.


Sample workout

Here is something we could do to focus on keeping the lower back healthy per above, along with hitting pretty much every muscle group.

A) Treadmill warm up with spinal feedback ~45 minutes

->This would be a warm-up, not a workout. A jog perhaps, but not an attempt to set a personal 5k best.

I would have a good focus on having some spring in every step, to get some extra work in the plantarflexors. “Have a little bounce in your step” is another good cue. Or “make sure to get up on your toes each step.” We might be able to hit a few birds with one stone here.

B1) Spinal compression exercise 2 sets 30 seconds

B2) Hills and Valleys 2 sets 15 reps

C1) Squat 4 sets of 10 reps

C2) Spinal compression exercise 4 sets of 30 seconds

C3) Overhead Press 4 sets of 10 reps

-> I always have people do this standing, not sitting, as it’s less direct compression on the spine. With standing, you don’t have something directly pushing upwards on the sacroiliac joint. In the space case, we could make an argument sitting is desired, to increase compression. This would fit well in this circuit, helping keep things compressed while we are most concerned with decompression i.e. when we’re close to heavily loading our spine.

C4) Hills and Valleys 4 sets 12 reps

C5) Triceps exercise 4 sets 15 reps

-> We again can make an argument for sitting over standing for compression reasons. Rather than some type of cable extension,

We could be seated,

D1) Bicep Curls 3 sets 15 reps

-> Once we aren’t as concerned with spinal compression, I’d lean towards standing exercises. This way the entire body is getting loaded. It might not be a ton -in a bicep curl you aren’t holding much resistance relative to what your legs can handle- but it’s something.

D2) Band RDLs / Good Morning (what I like to call “band lean overs”) 4 sets 50 reps

-> May very well not be enough.

D3) Facepull variation 3 sets 15 reps

D4) Hip Flexor Extensibility

-> If the psoas stays the same size in microgravity, it can, relative to other muscles, get stiffer too. (Bigger muscle may be a stiffer muscle A smaller muscle is usually a less stiff muscle.) We want to work on things not getting too stiff.

We need to insure the lower back does not extend during this type of stretching. The psoas can play a role in spinal flexion and extension. We don’t want to be stretching our hip flexors like this:

(The goal is improving psoas extensibility in this case, not improving lower back extension. And we likely want to be stretching the rectus femoris, as it likely incurs similar cross sectional influence as the psoas.)

As letting the pelvis anteriorly tilt -big lower back arch- lessens the stretch. But this would probably work. Trunk not flexed; spine neutral:

One area we’re lacking with the above is any direct pectoral work. One reason that may not be judicious is astronauts spend a lot of time with their arms like this:
astronaut space suit internal rotation shoulders

The shoulders are in internal rotation. (Elbows are turned out to the side.) The pectorals internally rotate the shoulders. It’s probably a motion they do enough of. The pecs tend to get stiff in people on Earth, from computer work. Astronauts do a lot of this as well. We could still do some work for this area, changing the form up some, but the volume would need to be kept in check. Shoulder problems are notorious in astronauts, and stiff pecs can cause shoulder problems.

But that’s for another post.

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