VO2 Max

How It Works: VO2 Max Test

Why would anyone choose to strenuously exert themselves on a treadmill, jaws pried open by a wide tube, until they're breathing so laboriously they froth at the mouth? There’s a name for this unique brand of masochism. It’s called a VO2 max test. If you’re a physically fit person looking for a tangible method to track your aerobic endurance and set serious fitness goals, it’s a great resource, despite the likelihood that when you finish you may resemble a rabid animal on the verge of heat stroke.

If you're still with me, read on for my firsthand account of what a VO2 max feels like. Currently, only students in St. Thomas' Health and Human Performance Department perform the tests as part of their lab requirements, but the HHP Department is working toward offering this service to the St. Thomas community on a limited basis in the near future. A VO2 max test provides athletes – whether professional or recreational – accurate, personalized data they can use to tailor their training and reach their goals.

VO2 max explained

Translated literally, V represents “volume”; O2, “oxygen”; and max is short for “maximum.” In other words, the test measures the most oxygen a person can process. Dr. Paul Mellick, an assistant professor in the HHP Department, explained it well: "As you stand at rest your body uses ATP (adenosine triphosphate), which is a biochemical your body uses to help create energy, just to keep your cells alive. For the average person at rest, they use about 3.5 milliliters of oxygen per kilogram of body weight. But when you exercise, obviously that number goes up because more energy is required, and therefore more oxygen is required to transfer that energy to the systems that need it. The more fit you are, the more oxygen you should be able to use because you're better able to transfer more energy."

This is, essentially, what a VO2 max test measures. The higher your VO2 max, the better shape you're in. For males 18 to 25, the range for above-average VO2 max is between 47 and 60 mL per kilogram of body weight per minute (mL/kg/min); for women in the same age bracket, the range is 42 to 56. Men's maxes tend to run higher than women's because they have greater body size and, in effect, greater blood volume. Averages drop slightly with each successive age group. In general, we peak at age 20.

What accounts for a person's VO2 max? It's mostly about the blood, because blood is what transports oxygen to muscles and organs. The more one has, and the more hemoglobin-packed, the better. Other factors? A powerful heart to push all that blood where it needs go, as well as high capillary and mitochondrial density in the muscles.

Genetics definitely play a role, Mellick said, but virtually anyone can improve on their max through physical conditioning. "If you look at a guy like Lance Armstrong (VO2 max reportedly around 84) ... that guy can bike really fast, which means there's tons of energy being transferred, which means he's going to use a lot of oxygen. That's accomplished by adaptations in your heart and in your muscles."

Athletic experts generally agree that a training program that incorporates regular exercise at 70 to 80 percent of your VO2 max will result in those heightened adaptations.

Fun facts ... to the max

The highest VO2 max Mellick has ever recorded was for a 22-year-old male All-American cross-country runner at St. Thomas, who measured 80 mL/kg/min. The second best, also by a St. Thomas men's cross-country runner in his early 20s, was 77. The third? Seventy-six, in a professional kickboxer in his late 20s during Mellick's graduate school days in North Carolina: "He was just a freak of nature, and he'd never taken a VO2 max test. We asked him how long he'd run before and he said, 'Never more than a mile at a time.' He had some genetics."

All three scores, though phenomenal, are not even close to the current world record, 97.5, set in 2012 by then 18-year-old Oskar Svendsen, a Norwegian cyclist and the 2012 junior world time trial champion. Svendsen bested longtime VO2 max record holder Bjorn Daehlie, a 12-time Olympic medalist in cross-country skiing, who recorded a 96 in a test taken during one of his off seasons.

The test

Before I stepped on the treadmill, Mellick handed me a Garmin heart rate monitor, which I strapped around my chest. It measured my heart rate, which was analyzed in comparison to the changes in my oxygen output throughout the test. To my head, he snugly fastened a clunky apparatus – equal parts orthodontic headgear, scuba mask and horse blinkers – made mostly of plastic and neoprene.

"It'll take some getting used to," he forewarned.

He then asked for my best guess on a pace I could comfortably hold on a flat road but that was also challenging. "You should last anywhere between seven and 14 minutes," Mellick said. "If it's less than seven, it means the speed we chose was too fast. If it goes longer than 14, it was too easy."

The headgear held in place a long plastic breathing tube with a mouthpiece on one end. It essentially propped my mouth wide open so I couldn't swallow or speak. Otherwise, it wasn't that uncomfortable.

Mellick plugged the other end into a Parvo Medics metabolic cart – a $20,000 piece of equipment that analyzed my exhaled gasses – stationed beside the treadmill. (Contrary to popular belief, the air we exhale is less than 5 percent carbon dioxide, the rest roughly 16 percent oxygen and 79 percent nitrogen in a person at rest.) It's the same device NASA uses to ensure their astronauts are adequately fit to do time in outer space. The cart was attached to a laptop loaded with specialized software.

From the laptop, he had the ability to incrementally increase the intensity at which I ran by raising the incline by 2 percent every two minutes. Based on that, I should eventually reach an all-out effort that I had to try to sustain as long as I can. During that painful and short-lived space my body would move from aerobic metabolism to anaerobic metabolism, and my VO2 max number would be revealed. The idea is that the test would end only when my muscles were too fatigued to continue.

Mellick explained that during the test he would ask me every minute or so to signal my perceived physical state via a hand signal. Thumbs up meant, "I'm fantastic. VO2 max test? What VO2 max test?!"; palm-down and tremulous was, "I'm fading"; and thumbs down translated to, "Stop this insanity now." He also mentioned that, at St. Thomas, they use a treadmill versus a stationary bicycle to administer the test because running is a more natural movement to most people.

While he gave me the run-down, drool seeped from the corners of my mouthpiece. He noticed my self-consciousness.

"Oh, yeah. Forgot to tell you. You'll probably drool," he said. "Everyone does. Don't worry about it." Then he tapped a key on the laptop and the belt started to move. The test was beginning.

After a short warm-up, he increased the pace to the "challenging but doable" speed I held through the test.

For the first two minutes I felt sprite. After the first incline raise, my breathing thickened, and the back of my throat was uncomfortably dry.

After five minutes, saliva sputtered from my mouthpiece.

By the third increase, I was glaring at the digital clock on the laptop monitor. 6:05. I'd hoped to last 10 minutes, but I was already struggling.

"How you doing, Kelly?" Mellick asked on cue, delicately.

I signaled "I'm fading," but somehow I held on for another two minutes. Throughout, Mellick inquired about my physical state more of often, about every 30 seconds.

Immediately after the fourth rise, a surge of lactic acid flooded my quads, the headgear suddenly felt 10 pounds heavier, and I had to focus hard to stabilize my breathing. Within a minute I flashed him a "thumbs down."

"Fifteen more seconds?" he prodded, to which I reluctantly signaled "thumbs up." I can do this, I thought, but my eyes were fixated on the laptop clock, counting down every second. My once-upright running form was crumbling.

"Fifteen more?" he asked again, trying to eek a bit more out of me. This time I emphatically signaled, "thumbs down." I'd endured a little more than nine minutes. My cheeks were brightly flushed, my chest heaving erratically, my legs burning. I was spent.

Next stop: The Olympic games?

Once I'd cooled down, I didn't walk away with just a sweaty shirt. Mellick handed me a print-out packed with personal data – hard numbers that reflected all the nooks and crannies of my cardiovascular fitness. The most important figures are RER – respiratory exchange ratio – which measures CO2 in versus CO2 out and most importantly, VO2/kg STPD mL/kg/min: the number that marks the exact point at which my oxygen consumption plateaued while my exercise intensity increased – my VO2 max.

"Most people, when they're figuring out their target training heart rate, are setting it based on the standardized equation for their age group, which is 220 minus their age." Mellick said. "That's not very accurate."

He pointed to my VO2 max – 47 – on the printout, then drew my attention to my heart rate the second I hit it: 200. Under his calculations, I should be training between 140-160 heartbeats per minute, well under 179, where the all-purpose formula would have put me.

With this information, I can set forth on my lifelong quest to make the U.S. Olympic marathon team. Or I can crash train to run a blistering speed in this year's turkey trot. Probably the latter.