Exercise to improve g tolerance

Posted on July 5, 2017

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We’re thinking about the following populations:

  • Race car drivers
  • Fighter pilots
  • Acrobatic pilots
  • Space tourists
  • Mars landers

Impact sports, boxing, MMA, football, may find the neck training section helpful too.

  • Why can g forces be a problem?
  • How much can we withstand before injury?
    • How many gs for how long
    • Body positioning
      • Reclined seats
    • The neck is a particular area when it comes to injury risk
  • Exercise considerations
    • What’s our g tolerance for blacking out? Can we help prevent this with exercise?
      • Being unconscious during a tourist activity wasn’t on the docket!
    • Lifting weights can increase g tolerance how much!?
    • Aerobics
      • When it comes to gs, is it better…to be fatter??
    • Specific neck exercises
  • Rocket science as insight to how hard human science is

Why can g forces be a problem?

Einstein had the happiest thought of his life when he realized a man falling off a roof would be pulled to Earth by gravity, feeling weightless, yet he would also be accelerated toward Earth. That gravity -commonly thought of as a force- and acceleration could be viewed as equivalent. That’s all gs are. A measure of acceleration.

Most have had a sensation of falling. Be it amusement ride, airplane scare, driving over a big hill. When that happens we have a sense while the outside of our body is falling down, the inside seemingly moves up. Your stomach can feel as if it’s in your throat. Relative to the outside of our body, the inside isn’t pressing down the same way, but overall everything is still moving down.

No different than an elevator in free fall. While the elevator would fall, our body would move up within the elevator- we wouldn’t be pressing into the floor, causing us to be weightless.

If the elevator were accelerating upwards, our body would be pushed downwards. We’ll feel heavier.

You can imagine, make this elevator accelerate in a more extreme manner, this could be problematic. If the elevator is accelerating upwards our body, our bones, muscles, ligaments, tendons have to withstand a greater force. Blood is being pushed out of our head, into our feet, where we could blackout.

If we’re moving down in something extremely quickly -quicker than free fall- we’re going to raise up more significantly. That could be into a seat belt, which could be gnarly on our shoulders. It could also entail an excessive amount of blood being pushed into the brain. (Since our body is being held down, the blood moves up, relative to our body.)

-> If you’re wondering why you can be in an airplane traveling 400+ miles per hour and not feel anything, that’s velocity. Acceleration is how quickly you’re changing your velocity (speed), not what speed you’re going at. When you take off and land you do feel some type of change with your body in relation to the seat. That’s acceleration.

Most problematic areas

  1. Losing consciousness
  2. Neck injuries

Consciousness being the biggest concern for pilots. Lose consciousness, significant increase in probability you lose your life.

For the neck,

“The Navy found that 74% of F/A-18, 58% of A-4, and 30% of A-7 aviators surveyed reported some neck pain associated with high-G maneuvers.

Twelve of 89 pilots were temporarily removed from flight status for an average of 3 days because of injury.

The USAF completed a similar survey with five wings at three TAC bases involving 437 F-5, F-15, and F-16 pilots. Neck injury rates of about 45% over a 3-month period of time were found in F-15 and F-16 pilots. Major injuries of 13% were reported for the F-16 pilots and were greatest in pilots over 40 years of age.”

Physical Fitness Program To Enhance Aircrew G Tolerance

This has been a noteworthy issue for fighter pilots.

My (limited) experience with drivers is it’s more an endurance issue than anything else. If the neck gets tired, that’s a distraction from the task at hand.

While the g forces are high, they’re brief and manageable (barring a crash). Between that and the fact drivers are seated -they’re perpendicular to the acceleration- blood supply isn’t a problem. It’s more having to handle g forces over and over.

Space tourism and Mars is an interesting case. One might initially ask, “Why not accelerate more slowly?”

The slower you land, the more fuel you burn. For Mars, we’re talking landing propulsively, not with parachutes.

To do that requires fuel. The more fuel to land, the less fuel for other purposes e.g. the amount of stuff you can put on Mars.

SpaceX is hoping to put something around a 100 people on Mars at a time. We don’t want a good deal of them landing with a neck injury.

Even for space tourism, where the two most promising companies are using parachutes and a glider:

For Virgin Galactic, they’ve already been screening for g tolerance. Even with the hang glider technique, you’re talking potential 6gs. (That’s 6 times your bodyweight!) They’ve had to disqualify some due to blood pressure issues, and have plans of screening and training people for three days before their flight. You can jump out of an airplane with less than 15 minutes training! That tells you how quickly these planes are coming in.

Blue Origin hasn’t started taking deposits yet. We don’t know what their stipulations will be. Their landing will get up to 5.5 gs, but landing isn’t the only concern. You need to accelerate enough to get into space too. They list their launch acceleration at more than 3 gs for 150 seconds.

-> I’m not sure if Blue Origin is including touchdown. When SpaceX’s Dragon capsule hits the water using three parachutes (the amount shown in the BO video) it incurs 7.5 gs. Though BO may have some ways around this.

What are human g tolerances?

How much and how long until we enter injury territory?

When we take off, are we going to be facing the sky? When we land, will we be facing the ground? In those cases, we’re flying vertical but our bodies are horizontal- we’ll be accelerated front to back into our seats.

Or will we be positioned in some other manner? Changing how our body has to deal with the acceleration.

This is hard to answer, as a lot of factors are at play. Can we land the same way we took off, can we make rotating seats, how much extra mass does that add to the spacecraft?

For Blue Origin, you can see the plan to go straight up and down. Virgin Galactic plans to do more of a typical commercial airliner takeoff, while SpaceX likely needs a bit of both to deal with the heat of atmospheric re-entry:

Potential positions of launching and landing. Aerobraking = use the atmosphere, then retropropulsion means use thrusters. Credit: https://www.reddit.com/r/spacex/comments/6gbrvw/will_its_use_a_suicide_burn_to_minimize_gravity/

Aerobraking.

We have different tolerances to each position  We can understand our g tolerance based off everyday life. We can stand longer than we can be upside down; we can lay down longer than we can stand. Thus, we want to first be laying down, second be upright so blood is pulled to our feet, and try the best we can to avoid being upside down.

If you look back at the Virgin Galactic video, you’ll see during take off the passengers are seated. They’re initially perpendicular to the direction of the acceleration, like our Formula 1 driver. But when they land, the seats are rotated so they are again perpendicular to the acceleration. This is all to help g tolerance.

Yet another factor is how long we’re dealing with the g force. We can deal with quite a bit of acceleration, if it’s for quite a short duration. Our tolerance goes down rapidly:

Notice these aren’t large time gaps. We’re going from e.g. .01 seconds to 0.2 seconds, yet experiencing a large drop in tolerance (~15gs to 5gs for moderate injury risk).

4-6 gs is what SpaceX reports their Mars landings will be. Blue Origin 3-5 gs; Virgin Galactic ~6 gs. 9 gs is the max fighter pilots can handle, and that’s with special training and special suits. For reference, a commercial plane will get up around 1.2 gs, and Space Shuttle astronauts were exposed to only 3 gs.

We’re in the realm of this being a concern for injury risk. In the above graph, after 0.2 seconds at 5 gs and we’re in the moderate injury area.

Different body position, where tolerance goes up:

Trying to extrapolate out:

Not the easiest graph to read, but blue is for 3 and 5 gs. You can see, within a minute of this exposure a person can be at risk. (Note above, how being supine or prone (perpendicular to the acceleration) increases tolerance.)

The above graph is an extrapolation of old research. It doesn’t look like we have much, if any research to know how people will do at longer time intervals, such as minutes. You’ll also notice this research has the person either transverse (perpendicular) or longitudinal (parallel) to the acceleration. What if we’re in between? Like a seat reclined 45 degrees?

One idea of reclination is to decrease the distance between the heart and the head, to better maintain pressure within the brain. The head thus gets pushed forward of the shoulders. Not the most comfortable! Fighter pilots are careful not too have too much of an incline, ~15 degrees seems common, because of more neck issues.

Aerodynamics play a role too.

Here is one discussion on reclining seats, with a persuasive argument not much happens until you’re at least 45 degrees reclined. Some research to back that up:

But what does moderate injury risk even mean?

In these charts:

“Moderate injury includes slight injury of extremities, short-time unconsciousness, dislocation, and simple spine fractures.”

Human Tolerance To Rapidly Applied Accelerations

Um, probably not everyone’s definition of moderate! It’s crucial to bring up here while there is much discussion on g tolerance changing with position, for the area we’re most concerned with, the neck, position is not as big of a help.

Being perpendicular helps, right? But what does this remind you of?

Looks like whiplash from a car accident! The neck is susceptible to injuries at as low as 2g.

Acute Soft Tissue Neck Injury from Unexpected Acceleration

Credit: Determination of a Whiplash Injury Severity Estimator for Occupants in a Motor Vehicle Accident

We’ve more or less figured out the gs we need to avoid to keep people coherent. We’re good at avoiding anything serious. We’re not good at avoiding more basic neck trauma. (Fighter pilots aren’t dying from gs, but their necks are regularly hurting.) When we’re talking commercial experiences, that’s not something we can as easily get away with.

Exercise- for injury prevention and for having a more enjoyable experience

There is potential to help increase g tolerance by training in a centrifuge. That is a costly way to do things. If we can avoid it, we’d like to. 

Weightlifting

The most known maneuver to help increase g-tolerance is the anti-g straining maneuver. This is for when blood is going head to feet.

When we relax our muscles is when blood tends to come in. When we contract them, blood tends to go out. This is most obvious with the heart. It pushes blood out -contraction- then it relaxes to let blood come back in.

So the idea of this maneuver is to more or less squeeze the hell out of everything to prevent blood from going downwards, leaving more to stay in the brain. If you do this in your seat, you’ll feel your head getting tense, because we’re increasing our blood pressure. (A good thing when fighting gs.) This can increase g-tolerance by 4 gs!

When else do we do something like this? Heavy weight training! Heavy squatting or deadlifting and we start looking like a lobster from increasing our blood pressure.

Of course, you can squeeze for too long, and ironically cause yourself to pass out, the thing we’re trying to avoid. (Same is true of the anti-g maneuver. In a Navy manual I looked at, it’s recommended to avoid holding longer than five seconds.)

Resistance training has indeed been found to help g-tolerance:

-Linked earlier: Physical Fitness Program To Enhance Aircrew G Tolerance

To the tune of a 53% increase. Duration can be improved too:

SACM = Simulated Aircraft Maneuver. Credit: AMP Working Group 14 High G Physiological Protection Training.

Furthermore, bed rest has been found to decrease g-tolerance.

Credit: Issues on Human Acceleration Tolerance After Long-Duration Space Flights.

We can deduce a clear relationship between muscle strength and g tolerance.

With pilots, fitness is part of life. However, it’s worth playing with heavy training, 1-5 reps, for an amount of sets and reps perhaps equal to a typical plane session, to more closely approximate the maneuver.

One way to get quite specific is try and re-enact the maneuver with weight training. An isometric pulldown is one example:

anti g straining maneuver training

I like the pulldown more than a chin-up hold, because the feet are on the floor with the pulldown, so you can work on contracting the lower body muscles too, such as pulling against the thigh support above.

For a Mars traveler, we’re reaffirming what we already know- they should be exercising. But similar to pilots, some heavier training here and there could be a nice addition. Particularly say, the month before landing. (They don’t need it consistently as they won’t be doing the maneuver on a consistent basis.)

“Make the best of your experience”

For the space tourist, we have an insurance policy for not hurting your neck and not blacking out. Rather than only screen and have two day trainings, it would make sense for these companies to encourage their customers to get in shape, as there will probably be a months long waiting period before a customer’s launch. It’s no different than going on a big vacation where you know there will be a a lot of hiking- you should probably do some hiking beforehand.

It wouldn’t be good for business if people report paying hundreds of thousands of dollars, yet end it with a neck disc herniation, or miss some of their experience from being unconscious!

Average tolerances for visual impairment run from 2-7 gs. That’s a big range.

Credit: AMP Working Group 14 High G Physiological Protection Training.

Here’s one example which seems applicable. 6 gs in 10 seconds and you’re out:

Furthermore, it’s not all or nothing. You can lose your color vision first (gray out), lose your peripherals (tunnel), lose your vision but be conscious. None of which you want happening!

-> Granted, this could be an adrenaline rush, like riding a rollercoaster. I’m making the possibly wrong assumption space tourists care more about visuals than a rollercoaster rider. And down the line, if you’re hell bent on avoiding the g forces, you could go up in a balloon instead, but then you don’t get to experience weightlessness!

This is where yet another factor comes into play, which is how quickly do you get accelerated to a certain level of gs. The sooner, the more likely you knock out. (The body can adapt if given enough time.)

A, B, C, D, are all different degrees of getting a level of G. In D, we get there slowly, so we only get some visual symptoms. In B, we get there so quickly we immediately lose consciousness. In A, we get there super quickly, but we’re not there long enough.

They saw some stars, but only the ones in their head!

Between weight training and the straining maneuver, we could take someone at the low side of the spectrum, 2 gs, and get their tolerance to a level where they should be able to handle these endeavors.

Aerobics / cardio

While a healthy aerobic system is something we want, excessive aerobics, like marathon training, has been found to decrease g tolerance. This is something else we could screen customers for: encourage the big runners to lessen their miles a few months before their launch and or get them to lift some weights.

My hunch is too much aerobic training tends to weaken the body. Marathoners are often very skinny people, to where they may be making their muscles too weak, at least relative to most military personnel who commonly have some muscle. Weaker muscles can’t as effectively engage in the anti straining maneuver.

Some might ask is being fatter better. No. Higher body mass is better, but more body fat is not: more muscle is better, not indiscriminate size. (See.) That’s worth knowing, as heavier passengers are more expensive passengers. If we can avoid having obese passengers in favor of merely muscular ones, that’s great.

Neck training

Before going over this, someone may be thinking,

“Why not just have neck restraints for the passengers?”

As our main issue here will be the neck potentially getting in an awkward position, trying to resist all that force. Adding head restraints adds more engineering, more material, more mass, more money. It’s not out of the question down the line, but cost is THE issue with space travel.

Not to mention, the passengers are going to want to be able to look around. Having a restraint only activating at certain times, or limiting passengers who are paying hundreds of thousands of dollars? Not ideal. (This is a similar concern with having passengers lay down the whole time. Might not be as easy to look out the window, and it takes up more room, decreasing how many passengers are on board, increasing the cost per passenger. Or why only some first class seats is where you can lay down.)

In the Blue Origin video, as they increase the amount of gs, the person is becoming more reclined. Earlier in the flight then later in the flight:

But you can see the person is, obviously, still looking out the window. That’s an awkward position to load the neck in, as the neck is having to constantly resist being rotated even more. (Acceleration is pushing the nose to the right in the above, because the person is already turned some that direction.)

This is another issue with reclining the seat too far- visibility. You can see in this scenario if that person is reclined a tad more, they won’t be able to see much.

I mentioned for drivers, endurance seems to be more the concern. Where some typical resisted neck motions, for multiple sets of 15-30 reps is something I’ve seen work well.

(You could also do a 30 second hold in each position.)

That said, they do take some turns violently. Pilots certainly do. This can explain why some strength training hasn’t been found to be beneficial for pilots- the strength training isn’t violent enough.

This is where I like bands, as the elastic nature inherently provides a more similar reenactment.

Don’t forget rotation:

You could get fancier by simulating whatever position the travelers will be in, such as:

A combination of endurance and elastic work would be ideal for space tourists and astronauts. They get prepared for the longer duration holds, as well as the inevitable sudden jolts.

-> You can see some serious vacillations at the eight minute mark:

Final point- estimations are reality

It’s very much worth pointing out that seemingly all the research done on g tolerance has been on military subjects, and some astronauts. Compared to modern day people, very fit subjects. The tolerance of everyday people will almost assuredly be lower, barring no training. Call it an average 3 g tolerance instead of 4, and we have a more significant concern.

To complicate matters further, we did say body mass can increase g tolerance. People are heavier now, but more than likely they still won’t have as much muscle on them as these subjects. Modern life is a version of bedrest compared to the 50s.

The reality is we’re not going to know how people do until they start launching. A great deal of g research is 30-60 years old. The experiments the military did was fucking awesome insane. Nobody is getting away with doing that these days, least of all a private company. Instead, companies will do the best they can, people will sign waivers, and we’ll see what happens.

In my view, making physical preparedness an even smarter move. The point here is mainly that. Not we should at all avoid these activities. Rather, exercise, a physically in-shape body, makes almost any variable one can think of go smoother. G forces included.

-> If one does get whiplash, being physically active also improves the prognosis.

What characterizes individuals developing chronic whiplash?: The Nord-Trøndelag Health Study

 

One thing I love about looking at space is it gives insight into everyday Earth experiences.

Notice how much there is to consider here for a single aerospace variable. Entire conferences and books have been done on this topic. Thousands of pages written. You can do innumerable missions where barely any of this has to be considered if humans are not on board. In other words, notice how much humans muck everything up.

There is an inherent appreciation for rocket science. It’s a cliche for difficulty. Meanwhile we have space ships all over the solar system, we’ve landed multiple robots on Mars, SpaceX and Blue Origin have launched numerous times to space, much of this is based off math conjured up hundreds of years ago, yet humans haven’t completely left Earth for nearly five decades (even the International Space Station touches the atmosphere!), nor has SpaceX or Blue Origin launched a human yet. Companies with thousands of employees. Some dude and his garage has gotten to space:

The human factor is an under appreciated reason why rocket science is so hard.

Sure, healthcare workers could be better, but maybe give your doctor a break next time they don’t have all the answers. “It’s not rocket science!” Nope. It’s human science, the toughest one we have.

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