Warning- Longish, rather technical / number-intensive post ahead. If you are a total data whore and/or find exercise physiology utterly fascinating (like yours truly), then read on! If not, just don't say I didn't warn you.
Recently Audrey passed along some information about a kinesiology study at SF State ("Relationship between functional hamstring and quadriceps ratios and running economy in females") looking for test subjects. The study uses two groups of female runners -- a recreational group (ie, people like me) and a highly trained group (eg, high-end collegiate runners training 90-100 miles a week). The requirements for the recreational group were 1) having run a minimum of 2 times per week for the last 3 years, 2) being able to jog 7.5 miles per hour (8:00/mile) for 6 minutes on a treadmill, 3) jogging a minimum of 5 miles per week, and 4) between 18-45 years of age.
The study requires two lab visits. I had my first visit last Wednesday, which involved a body composition analysis & several metabolic / fitness measures including resting metabolic rate, VO2 max, running economy, ventilatory threshold, & max heart rate. (Pretty awesome, since that kind of testing normally runs $150+.)
When I was in college, I participated in a similar kind of study and it was a really interesting & informative experience. I'm also a total body science / data geek & think all of this kind of stuff is endlessly fascinating, so I was excited to get the chance to participate. Plus, I'm a firm believed that data-driven decisions are almost always the best ones, and the more information you have about what's actually going on in your body when you run, the more you can make informed choices about your training. (Should I do more speed work? More tempo runs? More miles? Is my long run pace too fast / slow? etc. etc.) Science FTW.
Just a couple of disclaimers first off -
- None of these pictures are mine (except the ones of the printouts). I did bring my camera in case there was something interesting to memorialize, but since it was just me and the researcher getting pictures of the action wasn't really possible. Also it seemed kind of rude to just start snapping pics of the equipment while he was trying to get set up, calibrate things, record data, etc. On the other hand, the pics that I found online are a pretty faithful representation of what it was like, so trust me, you're not missing out on much.
- I'm far from an expert on this stuff, and although the researcher was more than happy to explain the science of everything, I wasn't taking notes or anything so I'm mostly going off what I remember him saying or knew already or have been able to look up, but don't hold me to every tiny detail (and as always, do let me know if you ARE an expert at this stuff and anything sounds wrong).
When I arrived, the researcher had me complete a questionnaire about my general health, running experience & habits, PRs, etc, which took about 10 minutes. Next I stripped down to my booty shorts & sports bra (my instructions were to wear as little & tight-fitting clothing as possible) so he could take some body measurements (height, leg lengths, hips, waist, thigh/calf/ankle circumference, etc.).
Step 2 was the "BodPod," which is apparently the gold standard for analyzing body composition (fat vs. lean tissue) in terms of accuracy, speed, & safety. You may have heard of the "dunk test" method of measuring body fat, where a person is weighed on land and under water and body fat is calculated according to how much water is displaced. The BodPod is similar but relies on air displacement rather than water. This is why you have to wear tight / minimal clothing -- I even had to wear a swim cap (alas, I broke the first one with my mighty locks) because loose hair apparently throws off the air displacement. Socks are also a problem. While the dunk test is extremely accurate, it's also fairly involved & time consuming, whereas the BodPod only takes a few minutes. Also you get to stay dry the whole time which is a plus.
After getting weighed on dry land, you sit inside the electro-magnetically sealed BodPod, which uses very small volume changes & measurements of the resulting pressure inside the chamber to determine the volume of the person inside. Then it divides mass by volume to get the person's density, which can then be used to determine the percentage of lean tissue vs. fat. (You can read more about the technical details of how this works here.)
To get an even more accurate measurement (which he did with me), the researcher can have the person in the pod breathe into a tube in order to measure the person's average thoracic gas volume, or basically how much air is hanging out in your lungs. This gives a better measurement because it's further accounting for "volume" (the space in your lungs) that isn't actually body tissue.
Once the machine knows your mass and body composition, it can calculate your Resting Metabolic Rate, which is the minimum number of calories your body needs per day simply to stay alive and functioning if you were to, say, spend the entire day laying in bed not moving.
For me, an interesting theme throughout this entire process was actual measured results vs. the approximations you can get for the same things via internet calculators. This was actually one of the main reasons I was interested in participating in this study. I've had really vague ideas about what my lean body mass, resting metabolic rate, VO2 max, etc. based on stuff I've read, but I've been curious for a long time to know just how accurate those poor man's approximations are.
The ones for body composition seem to be reasonably accurate. From this online calculator:
And from the BodPod:
(The BodPod itself has a margin of error of around 2% -- because of this, they usually measure 2-3 times and take the average.)
Online Resting Metabolic Rate calculators seem to be less accurate:
I tried a few different online RMR calculators & all of them returned numbers around 1380-90ish.
Once the BodPod measurements were done, it was time to start the metabolic testing, which looked at VO2, ventilatory threshold, & running economy.
(OK -- Here's where it gets a bit technical. The results of the testing are pretty meaningless unless you know a bit about what those things are, how they're measured, & why runners should care about them, so in the next few paragraphs I tried to give some background. If you're already up to speed, you can probably skip this part.)
There are lots of models out there for predicting the performance of endurance athletes, but one of the most popular & reliable uses three numbers: VO2 max, lactate threshold, and running economy.
"VO2" refers to the volume of oxygen that a person is consuming per minute at a given time & is measured in milliliters per kg of body mass per minute (ml/kg/min). When we're not working that hard, our VO2 is pretty low (for example, sitting in a chair not moving, my VO2 was in the 4-6 ml/kg/min range). As you start to work harder, your VO2 will increase because your body needs to use more oxygen. At a certain point, though, your body will hit a ceiling where, even if you continue working harder, it isn't capable of burning oxygen any faster. That number is your VO2 max -- the maximum rate that your body is capable of consuming oxygen. Obviously having a high "ceiling" in terms of how quickly your cells can burn oxygen gives an endurance athlete an advantage.
Lactate is a by-product of burning fat & carbs for energy that has to be cleared out of the blood stream by the liver. Whenever possible, our bodies prefer to burn fat because a) we have a ton of it available, b) it doesn't take much oxygen to burn fat, and c) burning fat creates relatively small amounts of lactate that our liver can pretty easily keep up with. The downside of burning fat is that it is a SLOOOOW process. Fat is perfect for fueling low-intensity activities (walking & even easy jogging), but as you start to work harder and your body needs more energy more quickly, it switches to burning a mix of fat and carbs.
Burning carbs releases energy much faster than burning fat, but it requires more oxygen and produces more lactate. As you work harder and harder and start burning a higher and higher percentage of carbs, your liver has to clear out the lactate faster and faster. At a certain point, an equilibrium is reached where your body is generating lactate at exactly the same rate as the liver can clear it out. This is your lactate threshold (usually given as a percentage of VO2 max).
If you continue to work even harder, there will be more lactate than the liver can clear out, causing a build up, which eventually results in unpleasant sensations like burning muscles, gasping for breath, etc. (When you run a 5K or 10K, for example, you're running above your lactate threshold, which is why you can only keep up that pace for a limited amount of time. Half marathon pace often keeps you right around LT pace, and marathon pace is generally below it.) The higher your lactate threshold, the harder you can run for a sustained amount of time. For average, non-trained people, LT usually falls between 40-60% of VO2 max, & highly trained endurance athletes usually fall in the 75-85% range.
Running economy is the measure of how efficiently someone can translate oxygen into forward motion. Running economy is calculated by dividing the total amount of oxygen consumed per kg of body weight and dividing it by the distance run in kilometers. If two people consume the same amount of oxygen during a period of time but one person runs farther, then that person has better running economy. (You can see how this would translate into a better performance in an endurance event.)
The SF State researcher tracked VO2 and running economy. Tracking lactate levels requires taking blood samples every minute or two during the treadmill test, which this study didn't do, but he did track something called ventilatory threshold, which is apparently a pretty good proxy for LT. (VT is essentially the point where rate of respiration sharply increases due to reaching LT -- you know you've reached it because it suddenly becomes extremely difficult to talk.) For the metabolic testing, the researcher had me wear a mask with a mouth tube while I ran on a treadmill, which collected all of the air I exhaled. (I had to wear a nose clip so that I could only breathe in and out through my mouth.) The machine could then compare the amount of oxygen in the air around us (he measured it before we started) to the amount in the air I exhaled to find out how much I'd used.
It was pretty much like this. (source)
Basically, the idea is to make the person work harder and harder (faster treadmill speed, more incline) and use measurements from the exhaled air together with what you already know about the person's mass and RMR to track VO2, respiration rate, and running economy. VO2 max will be the highest rate of oxygen consumption s/he reaches before falling off the treadmill (or, more preferably, communicating to the researcher via pre-arranged signals when s/he is too exhausted to continue).
Got all that?
(End technical-ness, mostly)
Wearing the mask is a little annoying because it forces your mouth into kind of a weird position. It's also sort of gross because you can't really swallow, and once you get a few minutes in it's just kind of spit everywhere. (Indeed, the mask has its own little 'spit collector,' but not everything makes it in there.) In between the early stages, the researcher would give me a towel and I would do the best I could to keep from dripping all over myself & the treadmill, but if you ever do this kind of testing you should just be prepared to be sort of spitty & slimey after a while.
First, I just sat in a chair & breathed into the mask so he could get a baseline VO2. (The machine would take a reading about every 30 seconds or so.) Next I had 10 minutes of really easy jogging as a warm up, and then the test began. I can't remember now what all the stages were -- I think I first jogged at 6 mph for six minutes, then 7.5 mph for five minutes, then got a five or six minute break. Every few minutes, he would hold up the Borg scale (left) & I would have to point to how I felt. I don't remember how many more stages I got through, but each one had a set amount of time you had to get through before the next stage began (eg, you had to last five minutes at 8.5 mph before going to 9.5, you had to last three minutes at 9.5 before he increased the incline to 3%, you had to get through two minutes of that before he'd make it 5%, etc. etc.).
At first, this was pretty easy. I had a heart rate monitor on with the display in front of me, so I had a sense of how hard my body was working & how much farther it had to go. I'm not used to running on a treadmill (I kept trying to go faster than the belt & running into the front of it) so that kind of messed with my perceived effort at first, so I was really glad to have something objective to rely on. Once I got passed the longer, slower stages, things got very hard very fast.
When I got to maybe the 5th stage or so, the researcher had left the computer & instead parked himself right by the treadmill & became my cheerleader, yelling things like, "Come on, you can do it! Keep it up! Keep pushing! I know you can finish this one! Two minutes left! 100 seconds! 90 seconds! 80 seconds! Less than a 200! Can you do more? 10 seconds more? 7% incline, you can do it!" This was actually pretty entertaining, or it would've been had I not been gasping for breath & slobbering everywhere while I tried desperately to stay on the treadmill.
At some point he stopped telling me the mph but in that final stage I was running really, really hard (maybe in the 6:00/mile range? I don't really know) with like a 7% incline & gasping for breath. It was definitely that last-10%-of-a-race kind of feeling when you're going SWEETBABYJESUSJUSTLETITEND!!! He did warn me ahead of time that no matter how far I got and how hard I pushed myself, as soon as I stopped I would feel like I could've gone longer & stopped too soon, but I must say, I feel pretty darn honest about how long I was able to hold on. I was drenched in sweat, gasping for air, & literally holding onto the treadmill for support for a good minute or two afterward.
Back to that whole thing about using calculators & formulas to approximate things that are hard to measure --
When I didn't know much about heart rate training (not that I know a ton now; just more than I used to), I remember using the old "mhr = 220 - age" formula, which, for me now, would predict a MHR of ~189. Imagine my surprise when I got my first monitor & started seeing numbers above that pretty regularly. There are tons of different equations out there for approximating MHR that take different variables into account (just google "calculate max heart rate"), but none of them have ever come anywhere close to predicting mine accurately. The highest number I have ever seen on my monitor is 223, but these days I routinely get up to 212-215 toward the end of races and that's about it. During this test, I got up to 211, which would indicate I was pretty close to all-out effort.
As for VO2 max, that's a little tricky even to roughly approximate, but the last time I tried I used the Cooper Test, which basically says, "Run as far as you possibly can in 12 minutes (in meters), subtract 505, then divide by 45," which gave me something like 53 ml/kg/min. This seemed rather on the high side, but during the treadmill test I apparently got up to 55.2 ml/kg/min, which is high enough for a recreational runner than he was a bit skeptical and re-checked all the equipment to make sure it was calibrated right. (The prediction based on all the other info he had about me & my running habits was somewhere in the 42-43 range.) Apparently average is mid-30s, most recreational runners top out in the low-to-mid-40s, and most of the highly trained collegiate women he tests get to 60-65ish.
He asked me again about how much I was running now & I told him that lately I'd been averaging between 30 & 40 miles a week. He seemed very surprised by this & said that it's extremely unusual for a 30-something female to have a VO2 max that high on that little mileage, meaning there is likely a strong genetic component at work. (Thanks mom & dad!) I guess everyone has their natural talents & apparently one of mine is ridiculous oxygen uptake.
As with most of my other unique skills and abilities, I am still working on how to monetize this.
My ventilatory threshold occurred when my VO2 was 39.7 ml/kg/min, or about 72% of my max, which as I understand it is pretty good as well (though much more in line with expectations than the 55.2 VO2 max). We didn't specifically talk about my running economy at the time, and it didn't occur to me to ask (I was a little bit brain-dead after the test), so I'm hoping he can tell me when I go back for the second visit.
There wasn't a ton of time once the testing was done, but mostly what I gathered from him is that the mileage I'm running right now probably isn't letting me come anywhere near taking advantage of the VO2 max I have, and that just plain getting more miles in (or even doing some other kind of cardio cross training) is probably my best bet in terms of becoming a better runner. (Higher mileage = better performance? I'm sure you're shocked.)
I'm going back next Friday to do the flexibility & quad / hamstring strength tests -- more to come then. :)