Lab Rat

As I've previously mentioned, I've recently started working with the Heart Center in their new sports cardiology practice, performing exercise physiology testing on athletes and assisting on a research project examining the relationship between distance running and heart disease.  However, though I've become quite familiar with performance testing over the past several months, I'd never undergone any physiologic tests myself.  That changed recently when my friend Beth Glace, a sports nutritionist and exercise scientist at NISMAT, recruited me to take part in a study on the mechanisms of fatigue in endurance athletes.

Ultrasound looking at muscle glycogen stores.
All photos: Charlotte Freer

I took the train into Manhattan and walked uptown to NISMAT, which is an extension of Lenox Hill Hospital that specializes in sports medicine and athletic performance.  I met Beth and her co-investigator, Ian, who showed me around and took me through the various elements of the research protocol.  First, I had my height and weight taken, and I underwent an ultrasound of my quadriceps, as a means of measuring my baseline glycogen stores in the muscle.  (Though I'm still on a low-carb/ketogenic diet, my levels were pretty normal.)  Then, I hopped onto the treadmill for a VO₂max test, the first arm of the protocol.  In this case, it didn't really matter what my max was, as this was just being used to determine the intensity at which I'd need to run during the latter stages of the project.  But surprisingly enough, we ultrarunners can get a bit competitive about some fairly mundane things, so I was pretty fired up to see what kind of numbers I could hit.

The dreadmill, with all kinds of fancy equipment.

The test followed a standard protocol, which includes a very brief warmup followed by progressive increases in intensity, until the subject/athlete can't go any further.  I was placed on a heart rate monitor and affixed a plastic headset that held in place the tube into which I'd have to breathe.  This tube ran into an analyzer that measured the relative volumes, rates, and percentages of the various gases I inhaled and exhaled.  From this, Beth and Ian could see not only my VO₂max, but also my lactate threshold (technically my ventilatory threshold, I'll probably bore you with some details about the difference in a future post), and, via a measurement called the respiratory exchange ratio (RER, or sometimes just R) could also determine whether I was burning carbohydrates, fats, or a mixture of the two, at various intensities.

I began by walking on the treadmill at 3mph (20:00/mile), which increased by 1 mph each minute, until reaching 6mph (10:00/mile) at the four-minute mark.  From that point on, with each passing minute, the incline increased by 2%.  Beth informed me that the treadmill had a max gradient of 20%, after which (if I was still running) the speed would then increase to 7mph (8:30 pace) for a minute.  If I could somehow keep going for that minute, the test would automatically stop.  And so I arrived at my arbitrary goal.

If you've never had a VO₂max test before, it is a very brief, very exquisite sort of torture.  The goal is to push the athlete to run to their maximum effort; thus, the test needs to be difficult enough to induce exhaustion, but short enough that the athlete doesn't end the test prior to reaching their max due to accumulated fatigue.  For the first eight minutes or so, then, the test is rather benign, but as the grade pushes past 12%, it begins to get unpleasant quite rapidly.  After eleven minutes, I reached 16% and was really starting to feel it.  At twelve minutes and 18%, I knew I could at least get to the 20% maximum grade, but I wasn't sure how long I could hold it there.  I fought my way through the entire minute at 20% and briefly entertained the possibility that I could finish an entire minute at 20% and 7mph, but after about 15 seconds I gave a desperate signal to stop.

The numbers were pretty cool; it's amazing how much data is generated from these tests and what it can be used for.  I was able to reach a VO₂max of 4.59 L/min, or 70.1 ml/kg/min, which is a pretty solid value for an old man.  My ventilatory/lactate threshold occurred at 88% of my VO₂max, which is near the upper end of normal.  (Higher is better: beyond the LT, lactate accumulation occurs faster than lactate clearance, and the steady accumulation of lactate will lead to fatigue; thus, being able to exercise as close to max effort as possible before reaching that point is obviously beneficial.)  Most interesting to me were the RER values.  I didn't start burning carbs at all until I was nearly halfway through the test, and I didn't hit an RER of 0.85 (metabolizing 50% carbs and 50% fat) until the ten-minute mark, running at at 14% grade with a heart rate of 171.  (My max HR came in at 184, slightly above predicted.)  Beth described this as very unusual, but consistent with the theory behind the ketogenic diet.  Nice to see that it's working.

Torture device.  I mean, the Biodex.

So that took care of the baseline testing.  I returned to the lab a week later for the main part of the protocol.  I began on a virtually empty stomach, having been instructed by Beth only to drink 13 oz. of Ensure about an hour prior to arrival.  After re-weighing and rechecking my ultrasound, I was seated on the Biodex, which was used to measure muscle contraction strength in my right quadricep.  Ian explained that first, they would measure a voluntary contraction, as I tried to extend my leg as forcefully as possible against resistance.  Then, they would provide stimulation with a magnetic field over my femoral nerve, which would induce an involuntary contraction.  Measuring the difference in the amount of force between these two, before and after exercise, would suggest whether fatigue was mediated by central (nervous) or peripheral (muscle) mechanisms.

Probably before I knew what was coming.

After strapping in to the seat, I pushed as hard as I could for about five seconds, and the force was measured.  Ian then positioned the magnet over the femoral nerve in my right thigh and induced a few isolated contractions.  It was forceful enough to make my body jump, but not painful.  Then came the payoff: I again gave a maximal voluntary contraction; after about three seconds, Ian introduced a continuous magnetic field, stimulating a sustained involuntary contraction as I continued to apply voluntary force.  As soon as he hit the button, I screamed; it wasn't painful exactly, but was one of the weirdest and most uncomfortable feelings I've ever experienced.  We did that twice more.  Then the real testing could start.

Waiting with dread...

The meat of the test was a two-hour continuous run on the treadmill, at 70% of my VO₂max.  Beth attached the breathing apparatus every fifteen minutes to ensure that I was maintaining the appropriate work rate.  My blood sugar and blood lactate levels were checked every hour.  When the two hours were up, the ultrasound measurements were repeated, and I was once again subjected to the Biodex, which remained just as unpleasant.  Then, back on the treadmill for a 2km time trial, as hard as I could push myself.  Then weighed again, ultrasounded again, and--you guessed it--the Biodex again.

Either really tired, or just anticipating getting back on the Biodex.

I'm not gonna lie, it was a pretty exhausting day.  But it was really interesting to see some of these processes in action, and I got a great feel for the different types of data that a treadmill test can generate.  I'll talk a little more about some of this stuff as the sports cardiology program starts to launch and I start seeing patients in the real world.