Editor’s note: This article was originally published on June 18, 2016.

In 2012, legendary BASE jumper Felix Baumgartner jumped from a helium balloon 24 miles above the Earth to set the record for highest-ever free-fall. Red Bull, the sponsor, had poured more than $65 million into the project and employed some of the world’s most eminent scientists and engineers to see it through, but the mission was nearly a complete failure — not because of any technical issues, but because in the months leading up to the jump, Baumgartner had developed a crippling fear of his spacesuit.

Even under the most extreme circumstances, undesirable emotions can be managed. The sports world realized that a long time ago, which is why today mental training is incorporated into nearly every professional sport. When Baumgartner tried to back out of the jump, Red Bull called in their secret weapon: a renowned performance psychologist named Dr. Michael Gervais, who quickly got the 43-year-old athlete’s anxiety under control. Baumgartner’s fall, which broke the sound barrier, was flawless.

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Elite athletes have benefited from performance psychology for decades, but it wasn’t until the 1990s that the U.S. military started to realize that it could be used to enhance battlefield performance, too. That realization owes largely to the efforts of then-West Point psychology professor Lt. Col. Dave Grossman, whose theories on the psychology and physiology of deadly combat, explicated at length in his best-selling nonfiction books “On Combat” and “On Killing,” draw heavily from what he hyperbolically refers to as the “multi-trillion dollar field of sports psychology.”

“The generals thought it was crazy,” Grossman tells Task & Purpose. “They said, ‘Just because it works in some stupid game doesn’t mean it works when someone is trying to kill you.’ We were looking at a fundamental question: Is the fear that you feel in the Super Bowl the same fear as the fear you feel in combat? The answer, it turns out, is yes. That’s huge. Anything that we can use in the athletic world we can use in combat. That’s one of the greatest revolutions of our time in improving performance on the battlefield.”

Of course, popular sports haven’t involved deadly combat since the fall of the Roman Empire, but, as Grossman is quick to point out, “Physiological arousal is physiological arousal.” In other words, on a physiological level, there’s no difference between preparing to free fall from the edge of space and preparing to kick down a door in an insurgent-held sector of Ramadi. In both scenarios, the brain and body kick into survival mode. And in both scenarios, even the most capable minds almost always experience fear.

Courage isn’t the absence of fear. It’s an ability to control it, or replace it with something else: anger, compassion, focus, loyalty to a cause greater than oneself. For a soldier, that ability can be enhanced by an understanding of how the brain and body function under extreme stress. Being able to identify these physiological processes, and knowing that they’re completely normal, can prevent crippling self-doubt, and thus more fear, from taking hold when they’re experienced in the heat of battle.

“We can educate people after the event, to help them understand and heal, but it’s much better to do it beforehand,” says Grossman. “We want a vaccine. Not penicillin. Forewarned is forearmed. If you are warned that these things will happen to your body they won’t blindside you.”

Task & Purpose joined forces with Grossman to do just that. In a series of animated graphics created by our own Matt Battaglia, we’ll walk you through what happens to a person’s brain and body before, during, and after battle. Over the decades, Grossman has interviewed thousands of combat veterans and law enforcement officials to develop the theories presented here. But consider this a primer. For a more in-depth understanding of the psychology and physiologically of warfare, we recommend reading “On Combat” and “On Killing.”

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 “Everybody interprets fear in different ways,” says Grossman.

On the eve of battle, emotions within any given combat unit range from excitement, to intense focus, to crippling anxiety. All of those feelings, Grossman explains, are completely normal:

“Everybody interprets fear in different ways. Take musicians, for example. One musician says, ‘I’m a mess before I go on stage. I feel like I’m going to throw up. I get really bad stage fright.’ But he still does a good job. The other one says, ‘Man, I get pumped up before the show. My gut is rumbling. My nerves are tingling.’ They’re both experiencing the exact same thing, but one gets eaten up by it, and the other gets pumped.”

There is, however, one feeling that’s very common among soldiers preparing for combat: the urge to defecate — or, as Grossman likes to say, “Take a battle crap.”

“In the lower abdomen in every human being is a toxic waste site,” he says. “The body’s response is to dump that toxic waste before a life and death event, because if there’s trauma to the abdomen that stuff will leak out and infect the wound. So, before the event, there’s often stress diarrhea.”

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The moment an engagement kicks off, the body initiates a dramatic response, beginning with the circulatory system, which immediately shunts blood away from the body surface. This, Grossman explains, is the body preparing to suck up damage.

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“It’s called vasoconstriction. Just before the capillaries, there’s a mechanical shutdown of the blood flow, and now the arteries and the body core are holding up to twice as much blood. That’s why the face goes white.”

There are two primary reasons for this. One, it helps prevent bruising, which is what happens when the capillaries and veins burst from blunt force trauma. If there’s no blood, they remain intact. But more importantly, the redirected blood flow helps keep the person alive long enough to finish the fight.

“Imagine it’s 5,000 years ago and a wolf is chewing on your arm,” says Grossman. “You’re caving its head in with a rock. Protecting your tribe. He can practically shred that arm and not get to the artery. You won’t bleed out in the heat of battle.”

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“There’s a dog inside every one of us,” says Grossman.

The death of a comrade is the ultimate nightmare scenario for any soldier, but while the heart grieves, the midbrain — the portion of the central nervous system that helps coordinate sensory information with simple movements and also controls alertness — kicks into high gear.

“I call the midbrain the ‘puppy,’” says Grossman. “There’s a dog inside every one of us. And when faced with sudden, violent death, the dog says, ‘Whoa, that could’ve been us. Pay attention.’ It’s a fundamental law of survival. Before you can help anybody else survive, you have to preserve yourself. So it’s an almost universal response to think, ‘Thank God that wasn’t me.’”

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That’s because, at its most extreme, vasoconstriction affects the brain, too. 

“As the blood drains from the face, blood drains from the forebrain, and there’s no rational thought,” Grossman explains. “I call that ‘condition black.’ And at condition black, the midbrain is in charge, and you’ll do what you’ve been trained to do — no more, no less. You will do what you’ve been programmed to do — no more, no less.” 

Thus, if a soldier reaches condition black and lacks adequate training, there’s a good chance he or she will freeze up. A well-trained soldier, on the other hand, will likely take action to neutralize the threat. 

“Given a clear and present danger, with today’s training almost everyone will shoot,” Grossman says.

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“The lion’s roar is a deafening, stunning event,” says Grossman. “But the lion doesn’t hear his roar, just like the dog doesn’t hear his bark. Their ears shut down, and so do ours. Gunpowder is our roar.”

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This phenomenon is called “auditory exclusion,” and it’s a result of the nerve that connects the inner ear and the brain shutting down in the heat of battle. According to Grossman, 90% of combat soldiers report having experienced auditory exclusion. “You get caught by surprise in an ambush. Boom. Boom. Boom. The shots are loud and overwhelming. You return fire, boom. The shots get quiet, but you’re still getting hearing damage.”

A soldier’s vision can also be affected by combat, and Grossman uses two different so-called predator models — the “charging lion” and the “wolf-pack dynamic” — to explain this.

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Most soldiers experience tunnel vision. “The charging lion is like a heat-seeking missile. He locks onto one target and never lets go,” he says. “That’s tunnel vision.”

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Sometimes, however, instead of zeroing in on his target, a soldier becomes intensely aware of all the moving parts on the battlefield, like a wolf hunting with its pack. “That’s what we want,” Grossman says. “When I work with high level civilian operators, like LAPD SWAT, it’s amazing to see how they’ve evolved. Almost all of them move between these two models: zooming in to eliminate a target and then back out to see everything going on.”

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There is another phenomenon involving vision that is widely disputed, but which Grossman insists is real, and that’s the experience of what he calls “slow-motion time.”

“I have had hundreds of people tell me they can see the bullet in combat,” he says. “Many have been able to later point to where the bullet hit, and they could not have done that without tracking the bullet with their eyes. Not like the matrix. It’s like a paintball, where the bullet is slow enough you can track it with your eyes.”

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The mind of a wounded soldier often envisions possibilities in the form of irrational thoughts or even hallucinations. This isn’t a psychotic episode, Grossman explains. It’s a survival mechanism.

“There was this police officer in Florida,” he says. “She was shot 10 times, and in the middle of this gunfight she says to herself, ‘I’m getting married in six months and you’re not going to stop me.’ And she killed the two bastards who shot her. She was back on the job a year later. So, yes, these are irrational thoughts, but at the same time, they’re motivating thoughts.”

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The fact that somebody is trying to kill you is bad enough without your mind and body doing weird and wonderful things. But if you’ve been warned about them, they won’t blindside you.”

“There are many ways people respond to combat, and there are many ways people respond to killing, and they’re all okay,” Grossman says.

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One response is what he calls “survival euphoria” — the feeling of euphoria experienced after a life-or-death event, like an intense firefight. “It’s the body’s natural response: I’m alive. It’s the satisfaction of hitting the target like you’ve been trained to do under the stress of combat. You stopped a deadly threat. You saved your own life. You saved other lives. It’s okay to feel really good about it.”

On a physiological level, something else happens after battle that can prove fatal if soldiers aren’t prepared for it: The body relaxes and blood flow begins returning to normal.

“You’re finally triumphant. You’ve caved the wolf’s head in. You won the battle. Then you relax and bleed out and die. So, it’s important to remember that the body will always backlash in the opposite direction. The wound that didn’t bleed out in the heat of battle will gush blood afterwards. That’s why today we immediately slap a tourniquet on the wound. People need to understand the importance of that.”

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For many combat veterans, the real struggle doesn’t begin until they’re thousands of miles from the battlefield, explains Grossman:

“We end up in this situation where people have this initial response of euphoria and then they backlash into a feeling of guilt. They think: ‘I killed that man and felt good about it.’ On a biological level, that midbrain — the puppy brain — doesn’t feel remorse for having had to kill. But then that other brain, the human brain, that sits on top of it says, ‘Oh, I should feel guilty about this.’ Then there’s this lifelong process of trying to rationalize that. But we can stop the whole thing right up front by letting them know it’s okay to feel good about it.”

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Anyone who’s watched a war film in the past 40 years is familiar with the concept of the flashback. It usually goes something like this: A soldier recently returned from war is walking down the street, he hears or sees something that reminds him of combat, and, boom, we’re transported back to the battlefield. That’s Hollywood’s overblown interpretation of a very real psychological process called “one-trial memory.”

“When you’re a kid, how many times do you touch a hot stove?” Grossman says. “One time. You touch it, scream, and a powerful neurological pathway is established. The midbrain says, ‘Don’t ever touch that stove again.’ But someone trying to kill you in combat is vastly more traumatic. And, as with the hot stove, this whole network of neurons is established and, unless you’ve been warned, you don’t even know it’s there. Then you hear a loud bang and your heart is pounding and you’re gasping for air. We warn people that the puppy may come for a visit. We warn people that they might re-experience all the intensity, fear, and physiological arousal of the event. It can turn into PTSD if you don’t deal with it properly, but by itself it’s not PTSD. It’s normal. It’s okay.”

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Many combat veterans have a tendency to avoid talking about war. Or, when they do, they speak about it in vague or dismissive terms. That’s natural. The brain simply doesn’t like revisiting traumatic events. But attempting to bury those hard memories only gives them strength, Grossman explains.

“You will literally drive yourself crazy trying to not think about it,” he says. “You will literally drive yourself down the path of mental illness. You got to make peace with the memory. You got to separate the memory of that event with the emotions associated with it. One of the techniques that’s taking off in the therapeutic world like a grassfire now is to simply take a drink of water while you’re talking about it. Taking in hydration is a powerful biological process that keeps the midbrain busy and helps it understand that we’re safe. It’s a simple way to separate the memory and the emotion, and just one or two times talking about it without the emotions coming along for the ride can completely sever that link. So, talking about it over a beer with your friends is actually amazingly healthy, unless you get drunk, at which point it starts becoming counterproductive.”

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On the heels of combat deployment, many, if not most, soldiers develop a deeper appreciation for the relative calm and comfort of civilian life. The thought of having to go back “over there” is almost unbearable. But that’s not always the case. Some soldiers, even those who’ve experienced the worst of combat, find themselves missing the battlefield. According to Grossman, there’s nothing unusual about that.

“You tap into that primordial model of the sheepdog, and there are people who continue to seek that, and there’s no shame in it,” he says. “I knew a guy who served several tours in Vietnam. He said it was the greatest experience of his life. A lot of guys were forced to go to Vietnam, but, aside from a few exceptions, nobody was forced to go a second time. They went again because they wanted to, because it was a highpoint in their life. There’s nothing wrong with that. We need those people, and they need to be able to be proud of who they are and what they did.”