For many reasons, not the least of which is their role in potential weight gain, carbohydrates tend to get a bit of a bad rap. Some famous diet plans go so far as telling us we should eliminate them completely. Some athletes even report they have gone “carb-free” (though quite what what they think fruit and most vegetables are comprised of, if not of carbohydrates, is a mystery).
The problem with this mentality is that carbs are not only important but they are essential in abundance if you are to succeed in your athletic goals. When it comes to training, we cannot afford to leave out this vital macro-nutrient; it’s the only thing stopping you from grinding to a halt 20 minutes into a workout.
“Hitting the Wall” – aka Crashing
Have you heard the phrase “hitting the wall”? Chances are you have, and I would even wager that, at some point or another, you have hit said wall. This happens when we don’t provide our muscles with ATP (adenosine triphosphate, the muscles’ main energy source) because we haven’t consumed enough glucose (the main fuel to create ATP). And any high-intensity activity we were engaged in suddenly becomes an exercise in sitting down and feeling weak. Wall = Hit.
What can we do?
Easy. Supply our bodies with enough fuel in the form of carbohydrates to maintain the exercise and then keep supplying it for hours after. Yes the amounts should be monitored so as to avoid hypo or hyperglycaemia but there are rules of thumb for these things and it’s fairly simple.
Well, OK, to be honest, there will be times when you will get the balance wrong (and it won’t be serious at all – bit of a stomach upset at most) but it’s all about finding what works for you and I’d defy the pros to get it right every time. Anyway, on to the science bit, I’ll try to be brief.
What Are Carbohydrates?
Carbohydrates are built from simple sugar molecules called monosaccharides, the most abundant of which is glucose, galactose and fructose. When two or more monosaccharides link together to make a chain, they become disaccharides (2 monos), trisaccharides (3) and so on (we can call them polysaccharides when they get too long to bother counting them).
Generally, carbs are lumped into two groups: complex and simple. This designation depends on the length of their chain. More importantly, the chains need to be broken down to the individual monosaccharides before they can be absorbed into the blood stream and used as energy. So, as you have probably guessed, the more complex the carbohydrate is, the slower it can be utilized by the body.
What is Glycogen?
Glucose can be used almost immediately to fuel metabolic processes. However, it can also be stored in the form of glycogen for later. Glycogen is in turn stored in the liver and muscles and becomes the body’s main store of energy for use during exercise. The size of this glycogen reserve depends on a person’s diet, training regime, size, insulin sensitivity (we’ll get to that) and so on.
Blood sugar is what keeps our brains fuelled and stops us experiencing mental fatigue. Mental fatigue equates to muscle fatigue no matter how much glycogen we have stored in our muscles. When blood glucose drops, our bodies replace it from the liver and when that is depleted we can get into trouble. This is why taking on carbs as we exercise can be vital. Even if our muscles are full of glycogen, that is being used for aerobic or anaerobic glycolysis to make our muscles work. If our brain isn’t fed then it is all worthless.
On average, we can store about 350 grams of glycogen in our muscles and another 90 grams in our liver. This can be increased pretty dramatically in athletes. The store of glycogen is good for up to 3 hours of medium intensity exercise but high intensity exercise could burn though it in just 30 minutes. And after it’s gone, the body has to source energy from elsewhere and it won’t be as efficient at all. One of those other sources is protein. Now, really, we want protein to be left alone to create an anabolic (growth) environment in our muscles and while certain supplements like Branched Chain Amino Acids (BCAAs) are a good source of intra-muscular fuel during exercise, it is better to keep our carbohydrate reserves topped up.
Fat is another excellent energy source but when we are deep into an intensely anaerobic workout, its the carbs that our bodies will access the quickest. It is worth mentioning here that fat is still burned during highly intense exercise but at a lower proportion than low-intensity. People often think losing fat is synonymous with low-intensity exercise but the truth is that high-intensity may burn less fat in proportion but it will burn more in total over an equal time period. So, if fat loss is your goal, you should still go hard at it for that hour long routine.
Developed so that diabetics could monitor their blood sugar levels as well as possible, the glycemic index is a system of categorizing foods. Rate of digestion is the biggest factor determining a food’s impact on blood sugar level. The slower the digestion rate, the less “glycemic” it is. Therefore, the glycemic index attributes a numbered rating to the food depending on its blood sugar elevating effect.
The index was originally designed to go from 0 (no blood sugar response) to 100 (maximum increase) but some really speedy digesting carbs are listed above 100.
Lower GI foods trigger a lower or less dramatic spike in insulin levels (the hormone responsible for nutrient partitioning) which can mean less fat is retained to use as storage. The average person, therefore, tends to be able to manage their carbohydrate and fat stores better with moderate to low GI diets. That’s not to say that simple (fast) sugars don’t have their place, but elevated blood sugar can lead to detrimental health conditions (including type 2 diabetes) if they are consumed chronically and in excess.
That said, high GI foods can be used to an athletes advantage and for the high intensity workouts, they have an important role. If you are interested in the different ways to supplement with carbohydrates before, during and after exercise, please look out for other posts.