Research: Sport Performance and Carbs Part 1

Writing about Carbs: Careful Now...
Writing about carbohydrates these days may be a risky enterprise, or, as Tina Fey writes (in a recent New Yorker column), a "tap-dance recital in a minefield." OK, Ms. Fey wasn't writing about carbs, just careers vs kids. That's, um, child's play compared to the aggressive food-fight going on right now between the pro-carbohydrate conservative traditionalists vs the Paleo/Primal low-carbohydrate rebels.

Don't know, actually.

This is a brouhaha which I will assiduously avoid here. But damn, I've already stepped into it by characterizing the factions the way I did. Anyway, they're focused on serious issues like heart disease, diabetes, and obesity. This post will focus instead on carbohydrate consumption as it relates to the petty issue of athletic performance, and primarily on post-exercise carbohydrate consumption for recovery, with accompanying largely irrelevant graphics from public domain sources, i.e., the government.

Glycogen
One of the oft-cited limitations of training volume, intensity and frequency is the availability of muscle and liver glycogen. Glycogen--stored carbohydrate--is the body's preferred fuel source because it rapidly produces energy. Glycogen provides most of the energy when we start to exercise. At low exercise intensities, fat is the preferred fuel, but as exercise intensity increases, so too does the percentage of glycogen used (source). During high intensity exercise, glycogen provides most of the energy and an athlete can deplete their muscle glycogen in just 30-60 minutes (source). Even aerobic exercise, if sufficiently intense, can deplete glycogen; in just two hours, virtually all of the liver and exercised muscle glycogen may be used up (source). Exercise physiologists often point to inadequate glycogen replacement in concert with intensive training as a cause of overtraining and chronic fatigue.

It is generally assumed, then, that restoring glycogen through carbohydrate consumption is of importance to training and athletic performance (source), particularly higher intensity exercise (source) and recovery. However, the particulars of carbohydrate consumption--when, how much, what kind, how frequently, etc-- is far from etched in stone.

Below is some of the salient research as I think it relates to the needs of rowers.

Twice-a-Day Rowers Perform Better on a High Carb Diet
In Dietary carbohydrate, muscle glycogen, and power output during rowing training., researchers randomly assigned twelve male and 10 female collegiate rowers to study whether "a high-carbohydrate (HI) diet (10 g.kg body mass-1.day-1) would promote greater muscle glycogen content and greater mean power output during training than a moderate-carbohydrate (MOD) diet (5 g.kg body mass-1.day-1) over 4 wk of intense twice-daily rowing training." It should be pointed out that the researchers also had the rowers consuming a fair amount of protein 2 grams per kilogram of body mass, and "fat intake was adjusted to maintain body mass" (which begs for some clarification). Anyway,  muscle glycogen content increased 65% in the HI group compared to no change in the MOD group and mean power output in time trials (2500 meters) increased 10.7%  (while only 1.6% in the MOD group). This led the researchers to write:

We conclude that a diet with 10 g carbohydrate.kg body mass-1.day-1 promotes greater muscle glycogen content and greater power output during training than a diet containing 5 g carbohydrate.kg body mass-1.day-1 over 4 wk of intense twice-daily rowing training.

Masters rowers take note: these collegiate rowers were training twice a day and with lots of intensity. You could argue that they were always in a state of recovery, something that is not necessarily true for many masters athletes.

Cows Perform Better Too

Eat Carbs Soon After Exercising
Various research seems to show a period of time when glycogen restoration is much faster. In Muscle glycogen synthesis after exercise: effect of time of carbohydrate ingestion., researchers showed that cyclists consuming a carbohydrate solution immediately after exercise showed much higher rate of muscle glycogen storage versus waiting for 2 hours (45% slower rate). Their conclusion: "The results suggest that delaying the ingestion of a carbohydrate supplement post-exercise will result in a reduced rate of muscle glycogen storage."

Does The Kind of Carbs Make a Difference?
There may be nuances to the above research. Subsequent research shows that the glycemic index of the carbohydrates may have some effect on the glycogen restoration rate. Glycemic index refers to a measurement of the effect that carbohydrates have on blood sugar levels. A higher glycemic index food generally has faster absorption of carbohydrates.

In Muscle glycogen storage following prolonged exercise: effect of timing of ingestion of high glycemic index food., researchers found that timing didn't matter so much as the glycemic index of the food and the quantity of carbohydrates. Their conclusion: "These data indicate that delayed feeding of a HGI meal by 2 h has no effect on the rate of muscle glycogen resynthesis at 8 and 24 h post-exercise, providing that sufficient carbohydrate is ingested during the recovery period." In other words, the magical 2-hour window in the first piece of research was shattered, if you will, by the nature of the carbohydrates.

It is noteworthy that this study only compared high-glycemic index consuming groups; in other words, the only variable was timing of the feedings. There was no low-glycemic index group with which to compare. However, the next piece of research did focus on that vary issue.

High Glycemic Index Carbs May Restore Glycogen More Thoroughly/Faster
In Muscle glycogen storage after prolonged exercise: effect of the glycemic index of carbohydrate feedings., researchers found that high-glycemic index meals at various intervals significantly exceeded low-glycemic index meals (by almost 50%) in restoring muscle glycogen. Their conclusion: "The results suggest that the most rapid increase in muscle glycogen content during the first 24 h of recovery is achieved by consuming foods with a high GI."

Catholic Carbs? Oops, nevermind. That would be Confirmation...

Eating a Big Carb Meal vs Small Carb Snacks, Doesn't Seem to Matter
Another variable in the carbohydrate conundrum is how the amounts of carbohydrates are consumed: large meals or nibbling snacks. In Muscle glycogen storage after prolonged exercise: effect of the frequency of carbohydrate feedings., researchers found that "there is no difference in postexercise glycogen storage over 24 h when a high-carbohydrate diet is fed as small frequent snacks or as large meals...".

Your Muscles Will Only Absorb So Much
One might imagine that if you only read the above research, you might consume lots of high-glycemic index carbs "early and often" to restore your muscle glycogen. Just how many carbs would you consume? This next piece of research tried to find some limits to carb ingestion. In Muscle glycogen storage after different amounts of carbohydrate ingestion., researchers had cyclists consume either a low amount of glucose or a high amount immediately and at 2 hours following glycogen-depleting exercise. The researchers' conclusion: "The rates of muscle glycogen storage...were not different..."

So, maybe I shouldn't eat the double stack of pancakes?

Does Protein with Carbs Help?
Several studies have found that protein taken with carbohydrate seems to enhance muscle glycogen storage. In Carbohydrate-protein complex increases the rate of muscle glycogen storage after exercise., researchers found that the rate of muscle glycogen storage was significantly higher with a protein-carbohydrate (112.0 g carbohydrate and 40.7 g protein mix) than with just carbohydrates (112.0 g carbohydrate) or just protein (40.7 g protein).

However, one criticism of a study like this one is that it is not an apples-to-apples comparison because the groups are not calorically equivalent (eucaloric). In other words, maybe it's not the protein that is enhancing the glycogen storage, but the fact that the protein provides additional calories. In Effects of postexercise carbohydrate-protein feedings on muscle glycogen restoration., researchers addressed this issue and produced results that suggested that "muscle glycogen restoration does not appear to be enhanced with the addition of proteins or amino acids [compared] to an eucaloric CHO feeding after exhaustive cycle exercise." So, maybe protein doesn't help?

But then there's the study that "tested the hypothesis that a carbohydrate-protein (CHO-Pro) supplement would be more effective in the replenishment of muscle glycogen after exercise compared with a carbohydrate supplement of equal carbohydrate content (LCHO) or caloric equivalency (HCHO)." You can read the details, but the conclusion is the title: Early postexercise muscle glycogen recovery is enhanced with a carbohydrate-protein supplement. So, maybe protein does help...

Confused yet? I was, so I looked at several carb-protein review articles. They seem to come down on the side of protein with carbs post-exercise. In Short-term recovery from prolonged exercise: exploring the potential for protein ingestion to accentuate the benefits of carbohydrate supplements., the authors write:

Some studies have reported improved physical performance with ingestion of carbohydrate-protein mixtures, both during exercise and during recovery prior to a subsequent exercise test. While not all of the evidence supports these ergogenic benefits, there is clearly the potential for improved performance under certain conditions, e.g. if the additional protein increases the energy content of a supplement and/or the carbohydrate fraction is ingested at below the recommended rate.

Well, that is a luke-warm endorsement of protein with carbs, but there it is.

Caffeine Helps Restore Muscle Glycogen
Like to have coffee with your oatmeal, french toast or pancakes following a good stint of rowing? Well, skip the decaf and maybe order the quadruple espresso because researchers have found that "in trained subjects coingestion of large amounts of Caff (8 mg/kg BM) with CHO has an additive effect on rates of postexercise muscle glycogen accumulation compared with consumption of CHO alone."

Translated into vernacular, that is 8 milligrams per 1 kilogram of body mass, which, in turn, means 584mg of caffeine for a ~161-pound/73 kilogram person. That is equivalent to 28 ounces of Starbucks coffee (about one and three-quarters of a Grande). See the Caffeine Post.

I'd Prefer a Flat White with a New Zealand Fern Leaf Cappuccino Art

Back to the research, in High rates of muscle glycogen resynthesis after exhaustive exercise when carbohydrate is coingested with caffeine., researchers asked trained cyclists to ride to "volitional" fatigue. Then they immediately had some high-carb meal, but some subjects additionally had some hidden caffeine with that meal (not in the form of coffee, in other words). The researchers didn't notice much of a difference in muscle glycogen resynthesis after an hour, but after 4 hours, the caffeine group experienced a 66% higher rate. I'll drink to that (as opposed to taking No-Doze or something).

About now you might be wondering: what combines high glycemic carbs, a bit of protein and caffeine...


Chocolate Milk: The Perfect Post-Exercise Beverage?
Various studies have shown chocolate milk to be at least as good as some carbohydrate replacement drinks in restoring muscle glycogen. For instance, in Improved endurance capacity following chocolate milk consumption compared with 2 commercially available sport drinks., 9 trained cyclists engaged first in a glycogen depleting trial and then immediately after and again at 2-hours after, drank either chocolate milk,  a carbohydrate replacement drink or a fluid replacement drink. Then they enjoyed the distinct pleasure at 4 hours to cycle to exhaustion at 70% power at maximal oxygen uptake. The chocolate milk cyclists (picture them with brown milk mustaches), lasted 51% longer than the carbo drink cyclists and 43% longer than the fluid replacement drink cyclists. Researchers concluded that: "[Chocolate Milk] is an effective recovery aid after prolonged endurance exercise for subsequent exercise at low-moderate intensities."

My post-exercise drink of choice: doesn't require refridgeration

Moderate or Low-Glycemic Meals Before Racing/Workouts
Several studies suggest that eating a high-glycemic index meal leads to poorer subsequent performance. As discussed before, carbohydrates come in different forms. Some are high-glycemic and raise blood sugar and insulin quickly, while others are slow absorbing and raise blood sugar more slowly (low-glycemic). For instance, an apple and a banana have roughly equivalent amounts of carbohydrates, but an apple is significantly lower on the glycemic index scale than the banana. (source)

In one study of equivalent breakfasts of different glycemic quality, researchers found that cyclists consuming a low-glycemic index meal produced a higher sustained plasma glucose level and 59% longer "time to exhaustion" in a 100% of VO2Max effort compared with cyclists who ate a higher glycemic index meal (but same number of carbohydrates). The researchers conclusion:

These results suggest a pre-exercise LGI [meal] may positively affect maximal performance following sustained exercise. The LGI maintained higher plasma glucose levels at the end of 2 h of strenuous exercise than the HGI, which may have better supported subsequent maximal effort.

This information might be useful for rowing events of longer duration, e.g., marathon rows, but it is not clear how applicable this would be for shorter events.

Another study with runners, found that "ingestion of a LGI meal 3 h before exercise resulted in a greater endurance capacity than after the ingestion of a HGI meal." This study had runners running to exhaustion and the LGI eaters ran significantly longer and burned more fat as well.

This last finding echoes several studies that suggest that higher glycemic pre-workout/pre-race meals inhibit fat burning during subsequent exercise. In The influence of high-carbohydrate meals with different glycaemic indices on substrate utilisation during subsequent exercise., researchers compared two "isoenergetic" meals, with substantially different glycemic indices (low and high), with another study condition, fasting (i.e., glycemic index of 0). The researchers found that the fasters used (oxidized) the most fat in subsequent exercise, the low-glycemic index eaters used the next most and the high glycemic index consumers used the least amount of fat.

Another study (with a really cumbersome title) reached the conclusion that "[a]lthough the LGI meal contributed less CHO to muscle glycogen synthesis in the 3-h postprandial period compared with the HGI meal, a sparing of muscle glycogen utilization during subsequent exercise was observed in the LGI trial, most likely as a result of better maintained fat oxidation." This suggests that, for longer events where you want to burn more fat and preserve glycogen as long as possible, you may be better off with a low GI pre-race meal. For shorter efforts, e.g., 1k or 2k rowing events, you probably don't care if you're burning fat or glycogen, or rather, you'd much rather be burning glycogen; otherwise, you're really rowing too slowly! On the other hand, at head races, if you have to row 5K to get to the start of a 5K, then you may want to heed this research.

Low-GI Carb rowers burn more fat and don't need seats!
Notice the Low-GI Carb rower floating near the ceiling. Take that, Red Bull!

It Looks Good For Low-Glycemic Index Meals and Subsequent Endurance Performance, But...
Two recent reviews of glycemic index foods and endurance performance (source and source) suggest that the state of knowledge at this point is inadequate to draw too many conclusions, with one review concluding: "the results have been inconsistent, with evidence of improved exercise performance in some studies, but not in many others." Sigh.

Accelerated Carbo-Loading
Participants in longer events sometimes engage in carbo-loading--consuming large quantities of carbohydrates for 2 to 6 days before some endurance event. One study of cyclists shows that you can get much of the same effect by training very briefly, but at sufficiently high intensity, and consuming sufficient carbs--all just 24 hours before an event. When this study means brief, they really mean brief: 150 seconds of 130% of VO2max pace followed by 30 seconds of all-out cycling, in other words, just 3 minutes of some really hard cycling. By the way, if 130% of VO2max sounds impossible, it is the pace not the oxygen consumption that they're talking about. If you know the pace required to elicit VO2max, then go 30% faster. For instance, on the ergometer, if my pace on the ergometer that elicits VO2max is 318 watts, then 130% of that would be 413 watts (or a split of 1:34.6) See, for example the VO2Max Calculator post.

After training, the above researchers had the cyclists consume high-glycemic index carbohydrates equivalent to 10.3 grams per kilogram of body mass. For a 161-lb person, that works out to be 751 grams or 1.65 lbs of potatoes, bread or overripe bananas. At 24 hours, these cyclists had the same amount of muscle glycogen as measured in carbo-loading regimens lasting 2-6 days.

Is Carbo-Loading Relevant to Rowers?
A review of available research on the topic shows "there is little or no effect of elevating pre-exercise muscle glycogen contents above normal resting values on a single exhaustive bout of high-intensity exercise lasting less than 5 minutes. Nor is there any benefit of increasing starting muscle glycogen content on moderate-intensity running or cycling lasting 60 to 90 minutes." Given that most rowing events are somewhere in the 4-25 minute range, carbo-loading may not be worth it. However, if you are rowing a marathon distance event, it may be.

Conclusions:
If you have waded through all the above, you deserve some take-home messages. Despite some of the inconsistent findings: I think there are some useful pointers for athletes who train sufficiently hard:

1. Insufficient carbohydrate consumption detracts from performance
2. Consume carbs immediately after "significant" exercise efforts. Despite the inconclusive nature of post-exercise timing, there seems to be little harm in eating soon after training efforts and there may be considerable gain if the glycogen absorption window exists.
3. High glycemic carbs pack a bigger punch.
4. Protein with carbs may be good, particularly if you can't get enough calories with carbohydrates alone.
5. Chocolate milk. Why not?
6. Caffeine may help, but I'd wouldn't drink coffee for this reason alone. Only one study so far.
7. Pre-race: low-glycemic meal seems better than high-glycemic, but somewhat inconclusive.

Again, I hasten to point out, I am only addressing exercise performance issues in this post, not health issues.

Part 2?
Researchers are addressing a variety of variables in carbohydrate consumption and athletic performance. Some folks are looking at low-glycogen training as a potential way to enhance mitochondrial generation (as intriguing as this is, it strikes me as playing with fire). Other researchers (example and example) are addressing the role of fat in diet in relation to carbohyrates (may work in slower, longer events). Many researchers are refining the time recommendations of carb consumption, before and after exercise. This might answer questions like: should I take that Gu right before the race. A few rowing races are long enough to require feedings during the race; that is something for a future post.

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Man lives for science as well as bread.

William James