12 December 2018

Metabolic test at Real Rehab Sports + Physical Therapy

Nerds love numbers! And when it comes to training/nutrition/gear/bike fit I am a huge nerd.

In the past, I have performed a VO2 Max test and when I heard about this Metabolic test from my friend Aaron Ostrovsky it sounded really interesting. Seems many of my friends like to geek out on the same stuff that I do (go figure...) so after learning about this, I had to do it too. What is a Metabolic test? According to Real Rehab where I had the test, "Active Metabolic Profile Testing provides insight into your efficiency in utilizing fat stores as energy during exercise."

Remember when every coach and sports nutritionist only ever talked about carbs? Well in case you have been living under a rock for the past 10 years, using fat as fuel and optimizing your bodies ability to metabolize fat is all the rage now. Not to mention Paleo, Keto, etc., etc.

If nothing else, you get some cool pictures when you do one of these tests.

Why this fascination with your body's metabolism and metabolic efficiency? It's pretty simple really. An average, healthy person can store about 500 grams of carbohydrate. Roughly 400 of these are stored in your skeletal muscle (frequently referred to as "muscle glycogen"), about 100 are stored in your liver, and the rest (25 grams or so) are stored in your blood and circulate through your body as glucose. These 500 grams are about 2000 calories of carbohydrate. The math is simple, one gram of carbohydrate contains about four calories. Protein is roughly the same by the way.

Fat, on the other hand, contains about nine calories per gram. Even a very "lean" athlete has at least 5 lbs of fat stores in their body, usually more like 8-10. Since most athletes (or people) are not super lean, let's assume 10 lbs to make the math easy. One pound is about 450 grams so that means each of us has a minimum of 40,500 calories stored in fat.

Let that sink in.

If we could burn fat as efficiently as carbohydrate or instead of carbohydrate, we would not need to eat for a very long time. That means as long as your body is able to metabolize fat, and you have fat to spare, it's pretty much impossible to bonk.

That, in a nutshell, is why so many endurance athletes are all talking about optimizing their fat burning engine/system. And a Metabolic test measures just how efficient you are at doing this.

I was told 70% of your fat burning efficiency is determined by your diet and only 30% is due to training. My takeaway from this is it confirms my belief that going for a run or ride without food to "train" your body to burn fat is dumb. Better to fuel your body while exercising and to eat properly when not exercising. If you do want to train your body to burn fat, exercise at an effort level that is conducive for this. For most folks, this is zone 2.

Here is how this test went down.
  • The test was explained to me.
  • I got fitted for the mask.
  • I took the test.
    • 10 minutes of warm-up which consisted of walking on a 2% incline at 3 mph.
    • Roughly 50 minutes of walking/jogging/running, every five minutes the tester would increase the speed and/or the steepness of the incline.
    • 5-10 minutes of cooldown to see how fast (or slowly depending on your perspective) my body recovered and was able to use fat as fuel again.
  • The results were explained to me and I got to ask questions.
  • I wanted to know how efficient my system was! As you get older you get slower but I had some of my best ultra trail running results ever in 2018 at age 54 due to better pacing and fueling. If this test could help me net an additional gain it would be awesome to stay the hands of time for another year or two.
Here are my complete results, and here is a great article from Uphill Athlete that will help you interpret the results.

Here is the Reader's Digest version (assuming I'm always running on a treadmill with a 2% incline).

Test duration: 50 minutes
Start: 2% incline, 3 mph (20:00 pace), 72 bpm
At 6.5 mph the incline was increased to 3%.
Finish: 3% incline, 7.5 mph (8:00 pace), 149 bpm
Crossover Point: RER (Respiratory Exchange Ratio) = 0.85
Metabolic Efficiency Point (same as crossover point): 144 bpm, 7.0 mph (8:34 pace) at 3% incline
  • This is roughly equivalent to a 7:51 mile on flat ground.
Zone 1: <83 bpm, <3.4 mph (17:38 pace)
Zone 2: 84-134 bpm, 3.5-6.4 mph (17:09-9:23 pace)
Zone 3: 135-147 bpm, 6.5-7.4 mph (9:14-8:06 pace)
Zone 4: >147 bpm, >7.5 mph (8:00 pace)

My recovery was slow. Within one minute of passing the crossover point/starting my recovery, my body was burning 100% carbohydrate and it took a full five minutes before it slipped under the crossover point (50% fat, 50% carbohydrate utilization).

This took two full hours from start to finish.


No big surprises here...!

If I run at 7.0 mph (8:34 pace) for an hour with a 3% grade my total calories burned is 1137 so I should consume 110-300 calories of carbohydrate-based snack every 1-2 hours. This supports my practice of "less is more" when fueling as I rarely consume more than 200 calories per hour during a race and even less if it's a 50k or shorter. Another way of looking at this is you should only consume 10-30% of your caloric expenditure per hour for a given effort.

Because it took my body a long time to recover and because the spread between my fat and carb consumption lines is not so great close to my crossover point, I should train more intervals. Basically, my body is used to churning away at a steady state and when I up the tempo, it has a hard time adjusting and I have a hard time recovering.

Interestingly, this is very much the same advice I got when I took my VO2 Max test. I guess I need to trust the science!

My recommended training week looks something like this.
- 2 days of zone 2/3 (5-10 minute intervals with 3 minutes of recovery)
- 1 day of zone 3
- 1 day of short zone 4 efforts with 5 minutes of recovery
- the remainder of the week should be no more than easy running/recovery or zone 2

  • Perceived effort is tough to convey. The tester kept asking me to rate my perceived effort on a scale of 1-10 after every 5-minute interval. I started at 1 and ended up at 7 for whatever that's worth. I think wearing the mask made it feel harder than it really was.
  • Running with a mask (that is attached to a very short tether) is rough. Turns out I bounce a bit when I run and I'm taller than most people they test. I also like to look around a lot. In this situation, you can't turn your head very far at all and you need to stay in just the right spot on the treadmill. Not so easy for me.

  • I was told my body is pretty efficient at burning fat! Considering how much my diet has been supplemented by chocolate and beer lately that is awesome news.
  • Once again these zone numbers confirm that my zone 2 matches up perfectly with the Phil Maffetone 180 Formula. You just can't prove that shit wrong. To burn fat, spend more time here (meaning in zone 2).
  • This test was another great reality check. Most athletes, including me apparently, spend too much time in zone 2/3, the "junk miles" zone. Instead, more of us should spend more time in zone 2 with occasional, short forays into zone 4. You need to mix up the pace in training to teach your body to go fast, move efficiently and to recover fast. And you need plenty of recovery in between these faster workouts.
  • Training by feel, except in very few cases (odds are you are probably not one of these), is not going to work if you want to maximize your potential. It will work just fine if you are only trying to maximize your fun or are just trying to live a healthy, active lifestyle. To really leverage this kind of data you need to use a heart rate monitor and/or a power meter.
Here are all my pictures.

Here is my not so accurate Strave file. For some reason, it appears my watch tried to use the GPS even though I selected indoor run so the distance is way short but the time is pretty accurate. The blip in the middle of this run is when I accidentally hit the emergency shutoff on the treadmill. :( We started it back up as fast as we could.

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