Hey, skydiver: What’s your mental image of hypoxia? Do you immediately picture a plane full of sport jumpers laughing like drunks and falling all over each other? If so, you’re not alone, and there’s also a good chance that you think a) you’ve never been hypoxic; b) hypoxia is just something that happens on high-altitude jumps when the oxygen system is on the fritz; and c) you know what to look for.

The thing is: You’re not actually right about any of that.

You probably remember Dr. Anna Hicks from the March issue, where we spoke to her about that most evergreen of skydiving questions: whether or not to jump with a cold. This month, we asked her for her notes on hypoxia (as informed by her decade-plus of boots-on-the-plane specialization in aviation medicine). If you like breathing, you’ll be interested.

Let’s Define It First

Hypoxia isn’t simply a deficiency of oxygen in the brain, as most folks think. Sure, an oxygen-starved brain is a very important part of the whole, but the actual definition of hypoxia is that there isn’t enough oxygen in the tissues. Hypoxia’s effects are most noticeable in the slow reactions and poor decision making it precipitates, but they reach far beyond that.

“When you’re hypoxic,” Hicks said, “you function less efficiently in general.”

Holding at 13,000? You’re Long-Since Hypoxic

If you imagine that the risk of hypoxia starts above 15,000 feet (the altitude at which the Federal Aviation Administration requires jumpers to use supplemental oxygen), you have another thing coming. According to aviation medicine, you’re at risk for hypoxia even at 10,000 feet. Most skydivers jumping from 12,000 to 13,000 feet on a normal jump are technically hypoxic long before they exit that plane. As it turns out, the average person’s oxygen concentration tends to drop to about 92 percent by a scant 6,000 feet above sea level, and mild symptoms of hypoxia generally make their appearance at 90 percent oxygen concentration.

You Might Not Know You’re Hypoxic

How can that be? Hicks explained, “Your body is designed to make it very difficult to recognize that you’re hypoxic unless you have had specific training in recognizing it.” That’s especially true since the early markers of hypoxia are similar to the symptoms of the excitement that jumping out of a plane is bound to cause: namely, an increase in your breathing and pulse rates. When these start to escalate to a tingling sensation in your fingers and toes—usually coupled with restlessness—you can be sure you’re looking at the progressing stages of hypoxia.

Night Jumps? Pass the O2

Remember what we mentioned earlier about hypoxia being a deficiency of oxygen in the body’s tissues in general? That comes into play in more noticeable ways at night. When the tissues of the eyes aren’t receiving a normal amount of oxygen, night vision suffers. Night jumps are inherently risky anyway, and especially so if you’re making poor decisions and can’t see. “The retina can’t function as it wants to do in a hypoxic body,” Hicks said, “and neither can the brain communicating with it. That means that the oxygen requirement for skydivers doing night jumps is greater, and jumpers need to start pre-breathing oxygen sooner.”

Your Home DZ Determines Your Set Point

Going out on the boogie circuit or to a training camp? Pay attention to the elevation of the drop zone you’re visiting. This goes beyond determining how much you want to downsize on that free demo canopy. It’ll help you determine your risk of noticeable hypoxia symptoms, as well.

Hicks warned, “If you visit a drop zone where the height above sea level is already high—like in Colorado, where you are already at 6,000 feet in the hangar—you’re already a bit hypoxic if you’re not acclimatized to living at that altitude. If you then go up to 12,000 feet, then you’re really going to struggle. As far as your body is concerned, you’re going up to 18,000. That can really affect your performance. Oxygen is really important, especially for big-way events and other situations where peak performance is key.”

The Bends: Not Just for Divers

You already know that you shouldn’t jump within 24 hours following a scuba dive. Did you know that going really, really up can put you at the same risk? If you are going higher than 18,000 feet above sea level, you might have an even more interesting concern on your hands than simple hypoxia: decompression sickness. Also known as “the bends,” “divers’ disease,” “aerobullosis” or “caisson disease,” this set of ugly symptoms pops up when nitrogen and other inert gases move from the blood into the tissues and then form injurious bubbles there. (When these bubbles form in the musculoskeletal system, they can cause lasting damage and debilitating pain; in the brain, they can cause symptoms of a stroke.)

Hicks noted, “I would recommend that any jumper jumping above 18,000 not just use oxygen in the aircraft; they should pre-breathe, too—sit in the aircraft at ground level pre-breathing pure oxygen for about half an hour. That pushes inert gases out of the tissues, minimizing the risk. When you’re going 18,000 feet above mean sea level with the military, you follow very strict pre-breathing rules. You simply don’t want to risk getting the bends.”

Check What Condition Your Condition Is In

Different factors can affect your vulnerability to hypoxia. Before you jump—especially if you’re going to a high elevation or it looks likely that you’ll end up holding for a while—take a thorough assessment of your current status.

“It’s known that cardiovascular fitness is a big factor,” Hicks noted. “If you’re physically fit, then your body is able to compensate a bit. But if you’re a smoker or are dehydrated or suffer from asthma or haven’t slept well or are hungover or are taking medications—like pain relievers or sedative antihistamines—take heed. Any one of those can increase your risk of more serious hypoxia symptoms.”

“If you aren’t in optimal fitness getting on that plane,” she clarified, “then you’re going to get symptomatic earlier, and that’s going to affect your ability to function much sooner than someone who’s in great shape that day.”

You Can Fight Back

If hypoxia is an unavoidable factor of skydiving—which it is—then it’s up to us to minimize its effects on our oxygen-hungry bodies and make sure we’re in the best shape possible. Luckily, Hicks insists that we have some weapons at our defense. First off, don’t fidget: Try to keep as still as possible, minimizing the amount of oxygen you’re using on the airplane. “Keep as still and calm as possible, especially if you need top performance,” she advised. “Even though your adrenaline is pumping, staying as calm as possible minimizes your oxygen requirement.”

Her second piece of advice is that if there is oxygen available, use it. “[Using oxygen] is the best possible thing that you can do to increase your performance and enjoyment,” Hicks insisted. “On oxygen, you’ll perform better, no matter what the jump. Full stop. The only way you could possibly overdose on oxygen is if you were to take it for several hours. It can only help you on a short-term-use basis.”

Hypoxia, then, becomes just another in a long line of examples that highlight the need for mindful self-awareness in our sport. There’s a poetry here, too: That oxygen that your body is so hungry for was born in the hot heart of a star. When you breathe it, it becomes part of you, too, and in some small way, you use each jump to celebrate the mad miracle that made that possible.

That makes you want to take a nice, deep breath, doesn’t it?

   Meet Dr. Anna Hicks

• Medical officer and an aviation medicine examiner with the rank of major in the British Army
• Consultant in family medicine and a British general practitioner
• Jumping since 2003 and has made more than 4,000 jumps
• Outside center for NFTO, which took silver in women’s 4-way formation skydiving at the 2018 Fédération Aéronautique Internationale World Championships
• British Parachute Association Accelerated Freefall Instructor and a formation skydiving coach

About the Author

Annette O’Neil, D-33263, is a multidisciplinary air sports athlete: skydiver, BASE jumper, paraglider and speed-wing pilot. Location-independent, she travels the world full-time as a freelance writer and producer. In her spare time, she loves flopping around on a yoga mat and carpetbombing Facebook from Instagram.