Haven’t heard of the glycogen window? It’s a period of time, roughly half an hour immediately following exercise, during which any carbs you ingest provide extra benefit in restoring muscle glycogen. In other words, if you exercise good and hard, you not only deserve a treat but are well advised to have one because it’ll help you recover. Among my racer pals, post-ride chocolate milk is all the rage. (Protein, calcium, and antioxidants are also touted as important recovery aids.)
I suppose I should add that this glycogen window thing isn’t widely viewed as hard science. I first read about it in “Bicycling” magazine back in the ‘80s; cycling hero Andy Hampsten wrote about it. I’d link to the article, but I doubt “Bicycling” has archived all their issues electronically like “New Yorker” has. (Perhaps “Bicycling” assumes their readers have no patience for text, especially old text that has been regurgitated countless times anyway, with articles like “It’s you—fit, fast, and self-trained!” and “10 easy ways to improve your power!” run in constant rotation.)
Naturally, I believed what Hampsten wrote because he won the Giro d’Italia and the Alpe d’Huez stage of the Tour de France. I began eating things like ice cream, fruit, or yogurt right after a ride or race, and immediately noticed an improvement in my recovery so I’ve stuck with it over all these years. (Yeah, it could be a placebo, but if so, it’s a strong one.)
In this post I will make a cursory examination of the evidence against the glycogen window theory, before presenting substantive proof, recently obtained from a very talented young scientist, that the glycogen window is for real. Here is the scientist, enjoying the fruits of her labors, both scholastic and athletic.
The case against glycogen window
It didn’t take long to find “evidence” against the glycogen window theory. The first Google hit came from an online magazine called evidencemag.com. I won’t summarize their arguments—you can read them right here—but suffice to say, I’m not impressed. This article depends entirely on a) other people’s research, and b) sentences beginning with “there’s little evidence that,” which only show the lack of information available to the author. Perhaps evidencemag.com will retract the entire article after reading this post and seeing my evidence.
One other thing: their headline is really wishy-washy: “Why Most Endurance Athletes Don’t Usually Need to Eat After Workouts” (italics mine). It wouldn’t hurt to define what an endurance athlete is, and why some would sometimes benefit. Meanwhile, this glycogen window thing (according to what I’ve read in support of it) only works if you do it as a standard practice—which means that nobody needs to do it sometimes.
That said, one thing mentioned in that article does present damning evidence against the glycogen window theory. It’s one of the footnotes, linking to an article that supposedly supports the notion: a book called “The Lance Armstrong Performance Program: Seven Weeks to the Perfect Ride.” Obviously, if Lance Armstrong—a known liar—says the glycogen window is legit, then it must be a myth, right? Well, it’s not actually that simple. You see, it’s clear Lance didn’t really write that book, but merely lent his celebrity to the project. So we’re still good.
You know what? I’m tired of paying lip service to the glycogen-window haters. You can research their silly positions on your own. It’s time to get to the proof that it’s valid.
Occasionally, I make the time to carry out scientific experiments on my own. For example, I proved that cyclists have extremely high pain thresholds (click here) and that rinsing—the practice of tasting something sweet without actually ingesting any calories—actually does increase athletic performance (click here). But I don’t have time to test every theory I come across. Thus, when I had the opportunity to leverage the considerable brainpower, time, and energy of my daughter Alexa, I jumped on it. (As I’ve documented here, I’ve long dreamed of exploiting my children’s intellect for personal gain.)
Here’s how I got my chance: my daughter was assigned a science project having to do with heart rate. It was supposed to be a fairly simple affair, such as measuring the heart rate of each test subject before and after eating chocolate. (Needless to say, it’s never a problem finding subjects for such a study.) Obviously Alexa could have done a really easy project like that, but you can guess what happened: I got involved and pressed my personal agenda.
It wasn’t hard to get Alexa to tackle a difficult research project, because a) as a budding athlete and lifelong lover of sweets, she has a vested interest in validating the glycogen window theory, and b) she knew she’d get some treats, in the form of candy and accolades, during the testing process.
Of course, using heart rate to measure the benefit of sports nutrition is not particularly straightforward. Alexa’s methodology involved measuring the change (i.e., delta) in heart rate between lying down and standing up. On the morning after exercise, this delta is usually greater than if the subject didn’t exercise the day before. Alexa sought to determine if getting a snack during the glycogen window reduced this morning-after effect. (Where did she get this idea? From me. I read it somewhere, ages ago, and a coach once explained it to me.)
You know what? Alexa describes all this better than I have:
One way of testing your recovery time is by comparing the delta of your heart rate between lying down (first thing in the morning) and standing up. After physical exertion, your muscles are tired, and standing takes more effort, raising your heart rate. This assumption is based off of the existing studies on the subject. My experiment will in part test this hypothesis. However, the main point is to examine the effects of getting a sugary snack within 35 minutes of exercising (i.e., during the so-called “glycogen window”). It has been proposed that getting this immediate sugar helps replace muscle glycogen (which is like the fuel in your car’s tank). This greatly enhances recovery (i.e., getting over fatigue). In my experiment, half of the test group will have some form of sugar after exercising, during the glycogen window. By comparing the delta of their heart rates, I will be able to see how the heart rates of the people who had sugar compare to that of the people who didn’t.
Alexa’s project got off to a fine start: she baked cookies for her friend’s soccer team. Half the team would get cookies right after soccer practice, and the other half would take cookies home to eat later. (Just try recruiting kids for the control group without offering them tasty snacks, too!) Unfortunately, the soccer practice got canceled, and though Alexa tried to get half the team to forego snacks after the next game, they all (predictably) flaked. So she got pretty far behind on her project.
I always try to strike the right balance between giving my daughter too much help versus letting her make her own mistakes. So, in this case I helped my daughter find replacement test subjects, but made her drive the project. This resulted in a real nail-biter: Alexa didn’t have all the data she needed until the morning the project was due. At 6:00 a.m. she was frantically collecting the final test results, writing her report, preparing her graph, and putting the whole thing together. (Perhaps this was the best thing about the project: she learned the hard way not to procrastinate, and got some good practice working well under pressure.)
Here is Alexa’s procedure, in her words:
Procedure: People participating will:
- Take their heart rate first thing in the morning.
- Stand up and take it again, recording the data, to get a baseline heart rate increase (aka “delta”).
- Exercise in some way (something aerobic) at some point during that day.
- Half of the group will have something sugary within 35 minutes of completing exercise; the other half won’t.
- The next day all will measure their pulse again, first lying down and then standing, and recording the data.
Alexa ended up with ten test subjects, their ages spanning 12 to 50-something. One subject was herself. I participated twice: I served as a with-sugar subject and then (a day or two later) as a without-sugar subject.
In the table below, a row shaded in yellow indicate a sugary snack was received within the glycogen window. I’m subject #1 and #2. Alexa is #3. My brother Bryan is #7. As you can see, getting a snack resulted in much less of an increase in the delta; that is, subjects recovered better when they had a glycogen-window treat.
Here is the conclusion Alexa wrote:
I have concluded that my hypothesis is correct, and having sugar after a workout helps you recover. The percent change in delta was in every case greater in the people who had no sugar after exercising. This shows that getting up was more of an effort for them, meaning that their muscles had not recovered to the extent that others had. This is illustrated by the graph. The red indicates people who did not have a sugary snack after exercising, and the blue indicates people who did.
Just look at this graph. The data unequivocally support her thesis.
Every responsible scientist notes certain caveats that could make the results less compelling, and Alexa is no exception:
In one case, the data set was not complete, and without a proper baseline delta, I couldn’t calculate that person’s percent change. If I were to redo the experiment, I would try harder to get that data in time.
Her final sentence is my favorite, with its unexpected twist at the end:
This evidence supporting my hypothesis could prove extremely beneficial in the area of after-sports snack debates.
Happily, Alexa’s findings guarantee that she (and her sister and I) will continue to get glycogen window treats after every serious workout. For me as a parent, this is a win-win because this coveted sugary reward guarantees my daughters will continue to do serious workouts. (Alexa will do a 45-minute trainer ride for just five or six jelly beans.) It’s touching to see these kids racing into the kitchen after exercise, jockeying for position and throwing elbows, yelling “Glycogen! Glycogen!”
A final note
I realize that neither Alexa nor I made any effort to prove that the lying-down versus standing heart rate delta actually means anything. But hey, we can’t do it all. If one of you would study that on your own and send me your results, that would be great. Or better yet, get your kid to do it!
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