Carbo loading- managing your glycogen intake without overloading on glucose.
Glycogen without glucose gluttony: your new carb strategy for optimum performance.
If you can work out a way to boost your muscle glycogen to supra-normal levels, your performances in athletic events lasting longer than about 60 minutes will be much improved. Glycogen is a key fuel during such exertions, but a basic problem is that, unlike fat, glycogen cannot be stored in your body in relatively limitless amounts. In addition, the glycogen in your muscles is quite rapidly depleted during fairly intense exercise, so that muscles begin to notice a shortage of glycogen after 60-90 minutes of activity. Yes, they can call on fat to provide fuel for further contractions and force production, but fat supports a lower intensity of exercise, and thus movement speed drops. This is why athletes who do a poor job of muscular glycogen replenishment before lengthy workouts, games or races usually slow down after 60 minutes, while their glycogen-loaded counterparts continue to work at the same intensity. So, the key question is: how do you make sure that you are amply glycogen-loaded? Once it became clear in the 1960s that glycogen was especially important during exercise lasting longer than an hour, Swedish scientists began to work at a furious pace to answer this question. A Swede named Ahlborg developed a protocol in which athletes performed a bout of very strenuous exercise and then consumed a high-carbohydrate diet for a period of three days while training normally (1). It worked! Athletes in the Ahlborg study boosted muscle glycogen above 150 mmol.kg-1 wet weight (‘normal’ levels are about 80-120).
There was just one problem, though – that strenuous bout of exercise. Usually, athletes want to be especially glycogen-loaded for a big race, and the notion of carrying out a very strenuous exertion lasting longer than an hour just three days before a big competition (in order to stimulate high rates of glycogen synthesis) was troublesome. Such efforts could interfere with tapering and could produce wear and tear on muscles which were frantically trying to heal themselves before a major event. Another problem also became apparent: athletes sometimes overloaded themselves during their three-day carb-fests. Instead of feeling unusually energetic, they ended up being bloated and sluggish on race day. The Ahlborg plan just wouldn’t do! Ahlborg’s colleague, a fellow Swede named Bergstrom, developed a slightly different plan. Bergstrom advised athletes to first engage in a rugged bout of strenuous exercise, then consu a high-fat, low-carbohmeydrate diet for three days (to really drive glycogen levels down), then undertake strenuous exercise again (just to make sure that muscle-glycogen levels were really low), and finally feast on carbohydrates for the seemingly magical period of three days, while training very lightly. This technique also succeeded in magnifying muscle glycogen concentrations.
The perils of strenuous exercise bouts before a major event
Again there were problems, however. Specifically, Bergie had failed to take into account the fact that two bouts of very strenuous, glycogen-depleting exercise during the week before a very important competition might be a bad idea. In addition, the three initial days of high-fat, low-carb eating left athletes irritable and less than super-confident. Finally, the three-day carbohydrate festival at the end of the Bergstrom protocol again left many athletes feeling gigantic and slow, rather than sleek and fast. Mike Sherman of Ohio State entered these troubled waters in the early 1980s with a very sensible and seemingly more practical plan for glycogen loading.
Addressing the paradox of recommending strenuous exercise during the week before a major event, Sherman’s stratagem called for no heavy exertion, and in fact allowed decreasing amounts of exercise on consecutive days. In Sherman’s six-day plan, athletes ingested a routine, ‘mixed’ (modest carbohydrate content) diet for three days and then stoked up on carbs for the next three days. Like the techniques developed by Ahlborg and Bergstrom, the Sherman stratagem ‘worked’, producing muscle glycogen levels above 150 mmol.kg-1 wet weight. However, the overall plan once again left many athletes feeling sluggish, and many individuals did not particularly want to cut back on training uniformly and relentlessly during their tapering periods, preferring to alternate days of doing almost nothing with days of performing modest amounts of quality work. In addition, many athletes wisely questioned the necessity of the initial three days of mixed-diet eating, and so Sherman’s plan was modified to consist of just the three days of high-carb eating, accompanied by successively lighter workouts.
Unafraid to enter this controversy, my own US newsletter Running Research News has for the past 10 years been recommending routine high-carbohydrate consumption (in the form of about four grams of carbohydrate per pound of body weight per day) for endurance athletes. This recommendation is based on research carried out by Clyde Williams and colleagues at Loughborough University, showing that endurance athletes engaged in serious training who consume less carbohydrate than this often end up gradually depleting their muscle glycogen stores, leading to lower-quality workouts and poorer performances. Our position has been that, if this strategy leads to routinely high levels of muscle glycogen, there is no special need to try to ram more carbs home shortly before races and extreme workouts. The reduced training employed in these times will allow extra glycogen synthesis to occur in muscles, and the chronically carb-rich diet will furnish the carbs necessary to get the job done.
Admittedly, though, the RRN plan is not without its own perils: for one thing, 4g of carbohydrate per pound of body weight per day has been shown to be a bit rich for some athletes, especially those who have previously restricted their calorie and carb intake. These athletes, many of whom may routinely take in just 2g per pound per day (we have even documented one quite successful athlete who was trying to get by with 1g!), may gain weight and feel extremely lethargic if they make a quantum leap to our ideal of 4g/lb/day.
So what’s the answer? Is there a simple, quick way to maximise muscle glycogen levels without fuss, extended periods of unusual eating or disruption of normal training?
In a word, yes! Thanks to research carried out at the Department of Human Movement and Exercise Science at the University of Western Australia, we now have such a plan (4). This plan takes just a day, and it produces incredibly high muscle glycogen levels!
Intensity and glycogen synthesis
The Western Australia work pivots around one key concept: very high intensities of exercise actually stimulate higher rates of muscle glycogen synthesis than moderate intensities of exercise carried out for prolonged periods. Naturally, athletes have been a little afraid to engage in very high-intensity exercise during their tapering, glycogen-loading periods, but the Australian researchers asked, quite reasonably: what if the intense exercise is just long enough to dramatically kick-start glycogen synthesis – but not so long as to interfere with tapering and recovery? In their ingenious plan, the Australians settled on a very short duration of intense exercise – just three minutes! Could such a brief period of exertion carry the broad load of heavy carbohydrate loading on its apparently puny shoulders? To find out, the Australians worked with seven healthy, endurance-trained male subjects. The athletes averaged 22 years of age, trained about 10 hours per week, possessed max aerobic capacities of around 56 ml.kg-1.min-1, and normally consumed about 6.6 grams of carbohydrate per kg of lean body mass per day (e.g. 3g of carbs per pound of lean body mass per day and 2.55g of carbs per pound of body weight per day).
Such intakes of carbs are fairly routine among endurance athletes, and thus the Australians had created a nice test of whether their one-day plan could really dramatically bolster muscle glycogen contents in typical athletes. On the morning the one-day high-carb diet commenced, the athletes had muscle biopsies performed on their quadriceps muscles (to assess glycogen levels), carried out a five-minute warm-up on a cycle ergometer, and then blasted through a sustained 150-second sprint on the ergometer at a very high intensity of 130% VO2max. At the end of this sprint, the athletes – without a second of hesitation – embarked on an all-out 30s sprint. Lactate levels at the end of this three-minute period of intense work soared to 21.9 mM/litre!
When carbo windows are open widest
Following a cool-down, each subject began the 24-hour high-carb eating plan, during which they ingested 12g of relatively high-glycaemic-index carbs per kg of lean body mass (e.g. 5.45g per pound of lean body mass and 4.6g per pound of body weight, just above the RRN recommendation). Crucially, the ingestion of carbohydrate was initiated within 20 minutes of the end of the exercise. (Remember that your muscles’ carbo ‘windows’ are open widest shortly after a bout of exercise ends; by two hours-or-so after exercise, they are open just a crack.) The participants ate high-carb foods they liked, including pasta, bread and rice but they also poured in extra carbohydrate in the form of the maltodextrose-rich drink Polycose, produced by Ross Laboratories in Columbus, Ohio. Indeed, about 80% of the carbs ingested over the 24-hour period came from this drink. The energy ingested as fat and protein, by contrast, was marginal – less than 10% of the caloric total for the day.
On the morning after the exercise and initiation of the carbo-loading regime, a second quadriceps muscle biopsy was taken. This revealed incredibly high levels of muscle glycogen; the mean glycogen concentration in the quads, which had been just 109 mmol.kg-1 wet weight before the trial, soared to 198.2 – an 82-% increase – afterwards! Analysis revealed that both slow and fast-twitch muscle fibres did an equally fantastic job of storing super concentrations of glycogen. The Australian plan was a real winner! It is the fastest glycogen-loading plan ever reported in the scientific literature. It also produces end glycogen concentrations (~198 mmol.kg-1 wet weight) which are extraordinarily high – considerably higher than the 131-153 readings often reported after three or even six days of traditional carbo-loading.
Preventing dips in muscle glycogen
The Australian research has several practical implications. If you are training strenuously, you need to worry about preventing dips in your day-to-day muscle glycogen levels. One way to do that is to routinely consume a high-carb diet, but another strategy – based on the Australian findings – would be to add in about three minutes of intense exercise near the end of many of your easy-to-moderate-intensity workouts. Such short periods of high-intensity work should not increase your risk of injury or burn-out, should enhance your fitness and should kick-start the post-workout glycogen-synthesis process, helping to ensure that you will have enough glycogen in your muscles for the next day’s workout. Of course, if your workout is already intense, there is no need to add anything to it.
This recommendation to slip in three minutes of intense stuff near the end of an easy workout may seem a bit bizarre, but it may well prove to be an exceedingly good strategy. Bear in mind that after fairly prolonged exercise consisting of only moderate-intensity work, it usually takes about 24 hours for muscle glycogen stores to return to pre-exercise levels, even when a high-carb diet is followed (6). The true glycogen-loading following such exercise does not really occur until the second and third days afterwards. By contrast, with the Aussie three-minute plan, super-loading occurs within the first 24 hours. Thus, it may be much easier to build – rather than merely maintain – muscle glycogen concentrations when a pinch of high intensity is added to workouts, and for some athletes the intensity may actually mean boosting glycogen levels back up to performance-enhancing levels (if they have been slogging away for a while with too-low levels of carbohydrate in their muscles). Note, too, how wonderfully well the Australian plan would work for a marathon runner (or other endurance athlete getting ready for a competition lasting longer than an hour). The athlete could follow his normal diet during the week leading up to the race, with no risk of bloating, lethargy, heaviness or gastric discomfort, and training could be tapered appropriately. The day before the big race, he could warm up, go hard for three minutes and then begin consuming large quantities of carbs. He should feel great – and have about 200 mmol.kg-1 wet weight in his leg muscles at the start line the following morning. He might even find his overall running fitness inched up a notch. Worried about three minutes of very hard running the day before the marathon? Perhaps it might cause your hamstrings to twitch a bit on race day? Don’t worry: you can carry out the 24-hour plan two – or even three – days before your major event and still go to the start line with supra-normal concentrations of glycogen in your muscles. Research has shown that once such concentrations are achieved, they can be maintained for a couple of days, providing athletes eat normal amounts of carbohydrate and do not carry out much exercise. Since you will be tapering, you won’t be doing much exercise, so all should be well. Here, then, is your guide to carbo-loading Aussie-style:
- Start eating carbs as soon as possible after you finish your exercise.
- Consume high-glycaemic-index foods during your 24-hour period, and don’t be afraid to include high-carb drinks like Polycose. Foods that count as high-glycaemic-index items (with glycaemic-index values above 60) include the following: croissants, crumpets, banana or apricot muffins, pancakes, waffles, scones, cranberry-juice cocktail, Gatorade, bagels, baguettes, bread stuffing, oat bread, white bread, flatbread, cornflakes, Pop Tarts, Raisin Bran, Special K, cornmeal, boiled sweet corn, couscous, most crackers and crispbreads, rice cakes, chocolate ice cream, apricots in syrup, dried dates, dried figs, papaya, raisins, watermelon, fruit bars, a plain pizza with cheese and tomato sauce, kugel, gnocchi, udon noodles, jelly beans, black-bean soup, split-pea soup, broad beans, parsnips, swede, most baked potatoes (especially if baked without fat), most boiled potatoes, mashed potatoes, and tapioca. You’ll need to read box labels and use nutritional charts to determine how much carbohydrate you are really taking in during your 24-hour period; remember that you are aiming for about 4.6g of carbohydrate per pound of body weight. If you fret about consuming high-glycaemic-index foods, bear in mind that many of the foods consumed heavily and regularly by élite Kenyan runners have very high glycaemic indices. For example, maize-meal porridge checks in with a glycemic index of 109. (The standard – glucose – is set at 100, which means that maize-meal porridge gets glucose into the bloodstream more quickly than glucose itself!) Another popular Kenyan breakfast item – millet-flour porridge – has a similarly whopping glycaemic index of 107. Kenyan rice – a true staple of the Kenyan runners’ diet – has an eye-popping glycaemic index of 112, and cornmeal – used to create the ubiquitous Kenyan national dish, ugali, has an index of about 70. Kenyan ‘wholemeal’ wheat flour checks in at 87, and chapati, a flat wheat bread settles for 66.
- Once you have completed your warm-up, three-minute burst and cool down, do not exercise again during the next 24 hours as this will damp down your muscles’ glycogen-synthesis rate.
- Don’t be afraid of the lactate you will inevitably generate during your three-minute surge. Remember that lactate does you no harm; in fact, there is evidence that the lactate itself may spur the increased rate of glycogen synthesis which occurs after intense exercise.
- The Aussie plan allows you to relax! If work or other pressures have kept you from carbo-loading as much as you would like before a major race, you can still do a tremendous job of stocking up on muscle glycogen during the last 24 hours before your event.
- Make sure you try out the Aussie regime a couple of times in training before you use it in competition. (By trying it out, I mean using the warm-up, three-minute burst, cool-down and 24-hour carb-eating scheme, followed by a long run afterwards.) There should be no major side effects associated with the plan, but you should at least prepare your body for it. If the regime doesn’t seem to be working well, try using the 24-hour plan two days before your long workouts or races, while carrying out little exercise and eating normally the day before the event. This intervening day may allow you to recover from your three-minute blast, without reducing your muscle glycogen concentrations.
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