Carbohydrates are to endurance athletes what protein is to bodybuilders. They are indispensable if you want to demonstrate the maximum of your capabilities.
Although it has been around for over half a century, a new wave of athletes have been experimenting with low carbohydrate intake during training and competition (the concept of adapting to the use of fat for fuel). This concept, coupled with the popularity of low-carb diets, has led many people to question the role of carbohydrates in their diet.
With this in mind, this article aims to reassure many of them and point out the cumulative benefits of consuming carbohydrates during endurance activities.
What are the benefits of carbohydrates for endurance athletes?
Those who develop endurance often train and compete at high VO2max (75-90% VO2max). Because all this happens at the limit of aerobic metabolism, and even beyond it; fat oxidation cannot meet the energy needs of contracting muscles.
In view of this, carbohydrates are primarily used as fuel, either extracted from the muscles (they are there in the form of glycogen), or consumed during sports in the form of sports drinks or carbohydrate gels, or both.
The usual amount of glycogen stored in the liver (which can vary depending on factors such as the degree of training and the level of lean muscle mass) is 100g. At the same time, the glycogen reserve in muscles varies from 300 to 500 g. All this can give you 1600-2400 kcal of energy until these reserves run out.
Exhausted Supplies
Glycogen is depleted in the thigh muscles after 90-120 minutes of continuous work at 65-75 VO2max. After this, you will feel very tired and will have to slow down (many of you are familiar with the phenomenon of the so-called “hitting the wall”).
If this is the case, endurance trainees must ensure that their glycogen stores are sufficient for the amount of work that needs to be done to perform at their best.
How are carbohydrates digested?
Let's clarify how carbohydrates are digested and absorbed.
It is known that carbohydrates are the main source of fuel for the body. When we eat carbohydrates, the body breaks them down into glucose, which is carried by the blood to the liver for storage or used by the muscles.
When carbohydrates are broken down into glucose and enter the bloodstream (often called “blood sugar”), the body releases the hormone insulin, which signals cells to absorb glucose. When the body does not need glucose for energy, insulin signals the body to store sugar for later use by creating glycogen stores in the muscles, and when these stores are already full, the sugar is stored as fat.
The food we eat is made up of three different macronutrients: proteins, fats and carbohydrates. Carbohydrates, in turn, can be divided into subcategories - simple and complex carbohydrates.
Simple carbohydrates, also known as “simple sugars,” are found in many foods such as fruits, vegetables and milk, and in large quantities in sweets and carbonated drinks (added sugars).
Eating large amounts of simple carbohydrates, especially in the form of added sugars, raises your blood sugar levels very quickly, causing excess fat to accumulate.
The rationale for recommending a low-carb diet for weight loss is that by reducing the amount of glucose in the blood, the altered insulin concentration will inhibit fat accumulation and promote fat oxidation. When insulin is secreted, glycogen (the body's carbohydrate stores) and fat will not be used for energy, meaning fat burning will be stopped.
How many carbohydrates do you need?
Although the optimal dosage varies from person to person and depends on the athlete's size and amount of work performed, endurance athletes are advised to consume 7-10 grams of carbohydrates per kg of body weight, which is about 60-70% of their total daily energy expenditure.
For those of you who like to run, but don't do it as much as advanced runners, you should start with 4-6 grams of carbohydrates per 1 kg of body weight. In the future, this dose can be adjusted to suit your current requirements.
To achieve these recommendations, you need to consume carbohydrates at the correct times, which will be indicated below.
Carbohydrates before workout
The purpose of eating before endurance training is to maintain the required blood glucose levels to conserve glycogen.
The pre-training period, in turn, can be divided into 3 stages:
- Days before training
- 2-4 hours before training
- Last hour before training
Pre-workout days (carb loading)
There are several popular strategies for maximizing your glycogen stores. The most popular of them is carbohydrate loading. This technique is used to end up storing more glycogen than normal (supercompensation).
Typically, this involves depleting glycogen stores for 3-4 days through exhausting training, followed by 3-4 days of carbohydrate loading (500-600 grams of carbohydrates per day) with a reduced volume of training. However, linear loading with carbohydrates (10-12 grams of carbohydrates per 1 kg of body weight for 1-7 days) appears in studies to be a more effective loading method. It is worth mentioning that carbohydrate loading will not affect the effectiveness of exercises lasting less than 90 minutes (given that the athlete initially had sufficient glycogen reserves), with the exception of interval, high-intensity exercise.
2-4 hours before training
According to research results, it is recommended to consume approximately 200-300 grams of carbohydrates 3-4 hours before training, if their intake during the training itself is not possible. The glycemic index of carbohydrates in this case does not matter - eat what you like best!
An hour before training
Since many people train in the morning before work, the recommendation to eat 2-4 hours before training is not feasible for them. In this case, I recommend taking 30-60 grams of carbohydrates, preferably in powder form (sucrose, glucose, instant oatmeal, maltodextrin, etc.), which you can mix with a protein shake.
Recovery after resistance training
Carbohydrates and muscle glycogen resynthesis
Resistance training depletes muscle glycogen stores. In fact, a single session can reduce glycogen stores by 24 to 40%, depending on the duration, intensity, and overall work done during the workout (42). Although research findings are mixed, if muscle glycogen is depleted and not promptly restored, it will negatively impact subsequent training (17, 25). Thus, consuming carbohydrates to prevent wasting or restore muscle glycogen can optimize subsequent resistance training.
To support this point, Haff et al. (17) examined the effect of carbohydrate intake on repeated bouts of resistance exercise during the second bout of a single training day. In this randomized, counterbalanced, double-blind study, 6 trained individuals performed similar resistance training, one week apart. The exercises were performed in the morning and afternoon, with 4 hours of rest between sessions. The morning workout was aimed at depleting glycogen in the muscles of the lower body. The second workout included squats to failure at an intensity of 55% RM at a pace of 1 squat every 6 seconds. Subjects were given the opportunity to rest 3 minutes between sets, with the goal of completing as many sets of 10 repetitions as possible. The lesson ended if it was impossible to complete 10 repetitions at the given pace.
During the morning workout, subjects consumed a 20% glucose-maltodextrin solution at a dose of 1.2 g/kg body weight per hour or a placebo containing no calories. After the morning workout and during a 4-hour rest, the carbohydrate solution was taken after 1, 2, 3 and 4 hours. The amount of carbohydrates was 0.38 g/kg body weight per hour. During the post-lunch session, there were significantly more sets and reps in the carbohydrate group (18 sets of 199 reps) compared to the placebo group (11 sets of 131 reps). The total amount of work completed was also greater in the carbohydrate group, but did not reach statistical significance (17).
Related to these findings, Leveritt and Abernethy (25) instructed untrained subjects to perform aerobic exercise after 2 days of carbohydrate-restricted eating to deplete muscle glycogen. The carbohydrate-restricted program caused a significant reduction in the number of repetitions of squats performed compared to a control group that did not deplete muscle glycogen.
Based on these two studies (17, 25), muscle glycogen restoration appears to be important for maximizing resistance training performance in subsequent bouts. However, if the target repetition range used in strength training is aimed at depleting the phosphagen system (3 – 5 reps are recommended for maximum strength gains), then the extent of glycogen depletion will be limited. Due to the limited number of scientific studies conducted in this area, additional experiments are required to confirm or refute these studies (17, 25).
The number of experiments aimed at identifying the optimal amount of carbohydrate intake after resistance exercise is limited. Table 2 summarizes the results of studies in which a certain amount of carbohydrate was consumed after strength training and how this affected muscle glycogen resynthesis.
Table 2. Glycogen depletion and replenishment after resistance training
| Study | Glycogen depletion after exercise | Amount and source of carbohydrates consumed | Amount of carbohydrates taken by a man (≈ 82 kg) | Effect on skeletal muscle glycogen |
| Pascoe et al. (31) | 33.00% | 1.5 g/kg body weight, taken immediately after and 1 hour later (glucose polymer) | 245 g (980 kcal) taken within one hour of training window | 2 and 6 hours after exercise, glycogen was restored to 87 and 91% of pre-exercise levels, respectively. |
| Roy and Tarnopolsky (38) | 36.00% | 1 g/kg body weight taken immediately after and 1 hour later (glucose polymer containing 56% sucrose and 44% glucose from corn syrup) | 164 g (656 kcal) taken within one hour of training window | 4 hours after exercise, glycogen was restored to 89% of pre-exercise levels |
Considering that 1 g/kg/hour is as effective as 1.5 g/kg/hour, it can be concluded that 1 g/kg/hour is sufficient to resynthesize skeletal muscle glycogen to 90% of pre-exercise levels. According to this dosage, an 82 kg man will consume 82 g of carbohydrates immediately after and an hour after exercise (total carbohydrates - 165 g within an hour after finishing the workout).
Carbohydrates with proteins and muscle glycogen resynthesis
Roy and Tarnopolsky (38) decided to determine whether protein supplementation with carbohydrates after resistance exercise was necessary to maximize glycogen resynthesis (compared to carbohydrate alone). In this study, each of the resistance training subjects consumed the following drinks immediately after and one hour after exercise:
- carbohydrate in the amount of 1 g/kg body weight
- isocaloric carbohydrate-protein-fat (66% carbohydrates, 23% protein and 11% fat)
- placebo containing no calories.
When reassessed 4 hours later, the carbohydrate-only group had muscle glycogen levels of 89% pre-training. Similar glycogen levels (89%) were observed in the carbohydrate-protein-fat group (approximately 72% in the placebo group). Results showed that consuming 0.67 g carbohydrate per kilogram of body weight, combined with protein and fat, was as effective as consuming 1 g/kg carbohydrate in restoring muscle glycogen stores (88).
Another interesting aspect of this study was the inclusion of calories from fat in the post-workout drink. It is often noted that adding fat to recovery drinks should be avoided due to its ability to slow the absorption and digestion of carbohydrates (which can negatively impact glycogen resynthesis). According to a study (38), adding fat to a post-workout drink does not have a negative effect on muscle glycogen resynthesis levels. In addition, when subjects received a post-endurance drink containing carbohydrates, proteins, and fats (even when the fat content was 45% of calories), the addition of fat did not affect muscle glycogen resynthesis or next-day glucose tolerance (14).
Proteins/Amino Acids and Muscle Damage
In addition to skeletal muscle glycogen resynthesis, optimal recovery also includes reduction of muscle soreness and suppression of muscle damage after exercise. In this regard, the consumption of BCAAs and protein shows beneficial effects.
Surprisingly, small amounts of protein consumed immediately after physical activity are highly effective. During a 54-day basic training period for US Navy recruits (13), just 10 g protein (together with 8 g carbohydrates and 3 g fat) was superior to placebo (no protein). Protein supplementation immediately following exercise resulted in a 33% reduction in total doctor visits, a 28% reduction in visits for bacterial/viral infections, and a 37% reduction in visits for muscle/joint problems, compared to the control and placebo groups. In addition, muscle soreness was assessed during the basic training period and on the last day of the program. The protein group significantly improved muscle soreness scores compared to the control and placebo groups. Study results show that post-exercise protein intake has a significant positive effect on health and muscle soreness during prolonged intense exercise (13).
Resistance exercise causes muscle soreness and, in fact, damage (32, 35). The primary goal of optimizing recovery from resistance exercise is to reduce muscle soreness, called DOMS (delayed-onset muscle soreness), and reduce muscle damage. Interestingly, BCAA supplementation was found to improve both aspects of recovery—DOMS and muscle damage.
In relation to DOMS, consumption of BCAAs reduces the soreness that occurs hours and days after eccentric (20) and high-volume resistance exercise (41). The dose for untrained individuals in the first study was 100 mg/kg before resistance exercise (41). In another study, untrained subjects consumed 100 mg/kg at different time points (for a total of 400 mg/kg throughout the day). In both studies, the ratio of BCAA intake (leucine/isoleucine/valine) was 2/1/1 (50% leucine, 25% isoleucine, 25% valine). To take this topic further, Sharp and Pearson (40) evaluated the effectiveness of BCAA supplementation in resistance-trained individuals over a 4-week period. Specifically, subjects consumed BCAAs for 3 weeks before and a week in conjunction with a high-intensity full-body workout. The subjects took 42 mg/kg of BCAA per day (in two parts - 21 mg/kg in the morning and evening). Skeletal muscle damage was measured through serum creatine kinase levels, which were measured before and after supplementation and after 2 and 4 days of exercise. Serum creatine kinase levels were significantly lower in the BCAA group during or after resistance training (compared to the placebo group).
Recovery from resistance training includes muscle glycogen resynthesis, decreased soreness, and decreased serum markers of muscle damage. Consuming a protein-carbohydrate drink after resistance training will restore muscle glycogen. Likewise, taking BCAAs improves recovery by inhibiting muscle soreness and damage.
Carbohydrates during exercise
The nutritional goals during endurance training are the same as before training—to maintain adequate blood glucose levels to conserve glycogen stores.
- For workouts longer than 90 minutes, I recommend 30-60g of carbohydrate per hour in the form of a sports drink or carbohydrate gel.
- For workouts lasting more than 3 hours, 60-90g of carbohydrates (per hour) will be the golden mean. For such high dosages, the use of carbohydrates such as glucose and fructose is recommended for better absorption and to minimize the risk of gastrointestinal upset.
Carbohydrates after exercise
After training, you need to take in enough carbohydrates to replenish glycogen stores. Anything less will eventually lead to progressive depletion of glycogen stores workout after workout.
For this reason, it is recommended that endurance athletes consume 200-300 grams of carbohydrates in the hours following training (noting that this should fit within the recommendations for total daily carbohydrate dosage). High-glycemic carbohydrates (potatoes, rice, pasta) are known to replenish glycogen stores faster than low-glycemic sources.
Those who exercise less intensely can stick to carbohydrate sources that taste best to them.
The importance of fast carbohydrates in human nutrition
Having a high glycemic index, fast carbohydrates can have a detrimental effect on human health. They do not provide the body with nutrients, and they dull hunger only for a short time. If sugar that enters the bloodstream is not converted into glycogen due to physical activity, it will be stored in the body as fat.
Therefore, all healthy nutrition systems recommend limiting the consumption of foods containing fast carbohydrates. You should be especially wary of fast carbohydrates in the afternoon; it is at this time that they pose the greatest danger to weight and figure.
A low glycemic index, on the contrary, promotes weight loss. If your goal is to lose weight, you can lose weight with a diet in which foods have a GI that does not exceed 55 units. In this case, a fit figure and a great mood are guaranteed.
When you eat foods containing fast carbohydrates, your blood sugar levels jump sharply. This is a negative factor for health and, according to doctors, can lead to the development of diabetes.
