How (and How Not) to Refuel

Here’s a primer on restocking the glycogen in your muscles after a hard workout.


When it comes to glycogen, the form in which carbohydrate is stored in your muscles, the basics are so familiar that we rarely think about them. After hard workouts, you need to seize the “window of opportunity” to replenish glycogen as quickly as possible; before a long race, you need to load up on carbohydrates to make sure you’re starting with as much glycogen as possible.


These remain, for the most part, good pieces of advice. But more recent research has added some subtleties that are worth considering. That’s the topic of a new review paper in the Journal of Applied Physiology, from Louise Burke of the Australian Institute of Sport, Luc van Loon of Maastricht University, and John Hawley of Australian Catholic University. Here are some of the highlights.


First, some background. If you were stop a random, well-fed but untrained individual in the street and extract a small sample of muscle from their leg, you’d find that the muscle contained about 80 to 85 millimoles of glycogen per kilogram of muscle.


If the subject happened to be a runner, you’d find that their muscles had adapted to hold about 120 mmol/kg. And if you happened to catch that runner the day before a marathon, after he or she had carbohydrate-loaded, you might find an impressive 200 mmol/kg. That’s a very big difference in the amount of fuel you’re carrying, and it’s why marathoners worry about getting their carb-loading right.


After a hard workout, you’ll deplete 50 per cent or more of the glycogen in the affected muscles, and it will typically take 20 to 24 hours before you’re able to completely refill them. So the first important question is: How do you refill those stores as quickly and fully as possible?


A study back in the 1980s introduced the concept of a “window of opportunity” during which your muscles can store glycogen more quickly. Eat carbs right after your workout, and you’ll restock glycogen 75 per cent faster than if you eat the same carbs two hours later.


What subsequent studies have found is that this head start doesn’t really matter unless you’re exercising again within the next eight hours or so. So if you’re working out once a day, you don’t really need to worry about it.


That doesn’t mean you don’t need to refuel properly! But if you head home from the gym and cook dinner rather than downing bars and recovery drinks the moment you finish, that shouldn’t be a problem as long as you’re getting enough fuel overall throughout the day.


Of course, there are times when faster recovery is important – if you’re training twice a day, competing in a meet with heats and finals, running a multi-leg relay, and so on. If you need to be as recovered as possible within eight hours, then starting the refuelling process immediately after the first workout is important. That has less to do with the “window of opportunity” than with the simple fact that it’s better to have eight hours of refuelling time than six hours.


For the most part, it doesn’t really matter what you eat as long as you can digest it. For that purpose, foods with medium and high glycemic index may have an advantage.

Adding some protein (0.3 to 0.4 grams per kilogram of body weight) to your post-workout carbs can also help glycogen storage rates. That’s 20 grams of protein for a 68-kilogram person, which is about what a typical protein bar has in it. Whether the glycogen boost from protein is really significant is debatable, but protein is a good idea anyway to help stimulate muscle repair.


There’s also some evidence that really ramming down a lot of carbs can help if fast (i.e., in less than eight hours) recovery is a top priority. The typical advice is to aim for about 50 grams of carbohydrate every two hours post-workout; but doubling that to 50 grams every hour for the first four hours seems to boost glycogen storage rates by 30 to 50 per cent. For reference, a PowerBar energy bar has 43 grams of carbs.


The authors have some sage advice about alcohol. It’s true that a few studies have suggested that alcohol slows the rate of glycogen storage after exercise. “However,” they write, “the most important effects of alcohol intake on refuelling (and other recovery issues) is through a reduced ability, or interest, to implement sports nutrition goals and sensible lifestyle choices.”


As for carbohydrate loading (or “glycogen supercompensation,” as they call it), the current evidence seems to suggest that you need 36 to 48 hours after your final workout to fully top up the glycogen stores in your muscles. During that time, you aim to take in more than 8 grams of carbohydrate per kilogram per day; I won’t do the maths here, but suffice to say it’s a lot, and will probably require downing some sugary sports drinks to make it all fit.

The overall point to emphasise here is to match your carbohydrate intake to your exercise or competition goals.


Stuffing your face with sugary “recovery” products immediately after a workout isn’t necessarily helpful if you’re not planning to exercise again until the next day (especially if the next day’s session is a relatively easy one) – and it can be counter-productive if those recovery kilojoules displace real food that you would have eaten had you waited until the next meal.



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