Category Archives: Nutrition and sport

Calories burned, water and minerals lost during running

Calculation of calories burned running

Running
Fig. 1 – Marathon

During running, energy expenditure is equal to:

0.85-1.05 kcal/kg of body weight/km

The range is due to the fact that athletes with a “cheaper” athletic technique expend less than those with a less refined technique.
Moreover, we must underline that  who have recently started running have expenditures even higher than 1.05 kcal/kg of body weight/km.

How many calories does a 70 kg (154 pound) athlete, with a good technique, expend if he runs for 10, 20, 30 or 40 km?
The expenditure/km is between:

70×0.85=59.5 Kcal and 70×1.05=73.5 Kcal/km.

For increasing mileage, omitting calculations, we obtain:

  • 10 km: 595-735 kcal
  • 20 km: 1190-1470 kcal
  • 30 km: 1785-2205 kcal
  • 40 km: 2380-2940 kcal

What does he consume during running?
He consumes:

Carbohydrate consumption during running

Carbohydrate consumption is affected, like for lipids, by the exercise intensity:

    • for running higher than anaerobic threshold, therefore the athlete is going very fast, only those are consumed;
    • in the pace typical of marathon, they supply 60-70% of the energy;
    • for pace lower than that of marathon, they supply less 50% of energy.
running
Fig. 2 – Exercise Intensity and Fuel Sources

During workout, energy expenditure is sustained, on average, for 60% by carbohydrates and the remaining 40% by lipids.

Carbohydrate consumption during workout

If we consider a 70 Kg (154 pound) athlete, carbohydrate consumption (in grams) to supply the aforementioned 60% for 10 km (energy expenditure between 595 and 735 kcal) is equal to:

(0.6×595)/4=about 90 g and (0.6×735)/4=about 110 g

where: carbohydrates=roughly 4 calories per gram.
For the other distances, omitting calculations, we obtain:

  • 20 km: 180-220 g
  • 30 km: 270-330 g
  • 40 km: 360-440 g

Lipid consumption during workout

With calculations as those made for carbohydrates, we obtain a lipid consumption (40% of energy) for the just seen distances equal to:

  • 10 km: 26-32 g
  • 20 km: 53-65 g
  • 30 km: 80-100 g
  • 40 km: 105-130 g

Arcelli’s formula

A formula, called “Arcelli’s formula”, exists by which we can estimate the grams of lipids consumed during running/walking:

grams of consumed lipids=(km x kg of body weight)/20 (30 if we walks).

Lipid intake, that are present in almost all foods, is not a problem, but it is very important because source of essential fatty acids, omega-6 and, above all, omega-3.

Daily protein requirements and running

Protein requirements of a sedentary man (adult) are equal to 0.8 g/kg of body weight/day (OMS source).
So, the basal requirements of the 70 kg (154 pound) athlete are :

0x0.8=56 g/day

About 3-5% of the energy expended to sustain muscular work comes from amino acids (coming from proteins) oxidation.
With calculations as those made for carbohydrates and lipids, for the just seen distances, we obtain:

  • 10 km: 61-64 g (0.87-0.92 g/kg of body weight/day)
  • 20 km: 66-73 g (0.94-1.04 g/ kg of body weight/day)
  • 30 km: 71-81 g (1.01-1.16 g/ kg of body weight/day)
  • 40 km: 76-89 g (1.09-1.28 g/ kg of body weight/day)

Leaving out athletes who train daily for 30 km or more, we obtain values slightly higher than 0.8/kg of body weight/day of the general sedentary population.
Actually, the amount is a bit to increase because some nitrogen (proteins) is lost with sweating as well as urine.
Howeve, we are always at lower values than 1.5 g/kg of body weight/day.

Fluid and mineral loss during running

Water losses depend on the amount of sweat that athlete produces that in turn depend on:

  • air temperature and humidity;
  • solar radiation.

The loss will be greater the higher these values are.
Finally, sweat is produced in different amount in any person.

By sweat, mineral lost are mostly:

  • sodium (Na+) and chlorine (Cl), about 1 g/L of sweat in athlete accustomed to train in environmental conditions that cause a great sweating;
  • potassium (K+) about 15% of sodium;
  • magnesium (Mg2+) still less, about 1% of sodium.
runner
Fig. 3 – Mineral Salts and Sweat

The amount of mineral salt lost depends on how much sweat we produce, and it increases if we consider not accustomed athletes.

Physical activity and sodium

During physical activity, the mineral we need most of all is sodium.
After physical activity, runner or who sweats very much (studies conducted initially on foundry workers) tends to eat saltier, both as food and as salt on food. We talk of “selective hunger”.
Probably, the “selective hunger” doesn’t not exist for potassium and magnesium (it seems that is not true for all subjects, usually 2 of 3).

References

Mahan L.K., Escott-Stump S.: “Krause’s foods, nutrition, and diet therapy” 10th ed. 2000

Sawka M.N., Burke L.M., Eichner E.R., Maughan, R.J., Montain S.J., Stachenfeld N.S. American College of Sports Medicine position stand: exercise and fluid replacement. Med Sci Sport Exercise 2007;39:377-390 [PDF]

Shils M.E., Olson J.A., Shike M., Ross A.C.: “Modern nutrition in health and disease” 9th ed. 1999

Shirreffs S., Sawka M.N. Fluid and electrolyte needs for training, competition and recovery. J Sport Sci 2011;29:sup1, S39-S46 [Abstract]

Wolinsky I., Driskell J.A. Sport nutrition: energy metabolism and exercise. CRC Press; Taylor & Francis Group, 2008

Glycogen: an efficient storage form of energy in aerobic conditions

What is the net energy yield for the oxidation of a glucose unit from glycogen in aerobic conditions?

Aerobic Conditions: Glycogen Structure
Fig. 1 – Glycogen Structure

In aerobic conditions, the oxidation of a free glucose to CO2 and H2O (glycolysis, Krebs cycle and oxidative phosphorylation) leads to the net production of about 30 molecules of ATP.

Glucose from the action of glycogen phosphorylase: glucose-1-phosphate release (about 90% of the removed units).

Glycogen synthesis from free glucose costs two ATP units for each molecule; a glucose-1-phosphate is released by the action of glycogen phosphorylase with recovering/saving one of the two previous ATP molecules.
Therefore in aerobic condition, the oxidation of glucose starting from glucose-6-phosphate and not from free glucose yields 31 ATP molecules and not 30 (one ATP instead of two is expended in the activation phase, 30 ATP are produced during Krebs cycle and oxidative phosphorylation: 31 ATP gained).
The net rate between cost and yield is 1/31 (an energy conservation of about 97%).
The overall reaction is:

glycogen(n glucose residues) + 31 ADP + 31 Pi → glycogen(n-1 glucose residues) + 31 ATP + 6 CO2 + 6 H2O

If we combine glycogen synthesis, glycogen breakdown and finally the oxidation of glucose to CO2 and H2O we obtain 30 molecules of ATP per stored glucose unit, that is the overall reaction is:

glucose + 29 ADP + 30 Pi → 29 ATP + 6 CO2 + 6 H2O

Glucose from the action of debranching enzyme: free glucose release (about 10% of the removed units).

The net yield in ATP between glycogen synthesis and breakdown is two ATP molecules expended because of free glucose is released.
In this case the oxidation of glucose starts from the not-prephosphorylated molecule so we obtain 30 ATP molecules.
The net rate between cost and yield is 2/30 (a energy conservation of about 93,3%).
Considering the oxidation of the glucose units from glycogen to CO2 and H2O we have an energy conservation of:

1-(((1/31)*0,9)+((2/30)*0,1))=0,9643

Conclusion

In aerobic conditions, there is the conservation of about 97% of energy into the glycogen molecule, an extremely efficient storage form of energy.

References

Arienti G. “Le basi molecolari della nutrizione”. Seconda edizione. Piccin, 2003

Cozzani I. and Dainese E. “Biochimica degli alimenti e della nutrizione”. Piccin Editore, 2006

Giampietro M. “L’alimentazione per l’esercizio fisico e lo sport”. Il Pensiero Scientifico Editore, 2005

Mahan LK, Escott-Stump S.: “Krause’s foods, nutrition, and diet therapy” 10th ed. 2000

Mariani Costantini A., Cannella C., Tomassi G. “Fondamenti di nutrizione umana”. 1th ed. Il Pensiero Scientifico Editore, 1999

Nelson D.L., M. M. Cox M.M. Lehninger. Principles of biochemistry. 4th Edition. W.H. Freeman and Company, 2004

Stipanuk M.H.. “Biochemical and physiological aspects of human nutrition” W.B. Saunders Company-An imprint of Elsevier Science, 2000

Maltodextrin, fructose and endurance sports

Carbohydrate ingestion can improve endurance capacity and performance.
The ingestion of different types of carbohydrates, which use different intestinal transporters, can:

  • increase total carbohydrate absorption;
  • increase exogenous carbohydrate oxidation;
  • and therefore improve performance.

Glucose and fructose

When a mixture of glucose and fructose is ingested (in the analyzed literature, respectively 1.2 and 0.6 g/min, ratio 2:1, for total carbohydrate intake rate to 1.8 g/min), there is less competition for intestinal absorption compared with the ingestion of an iso-energetic amount of glucose or fructose,  two different intestinal transporters being involved. Furthermore, fructose absorption is stimulated by the presence of glucose.

This can:

The combined ingestion of glucose and fructose allows to obtain exogenous carbohydrate oxidation rate around 1,26 g/min, therefore, higher than the rate reported with glucose alone (1g/min), also in high concentration.
The observed difference (+0,26 g/min) can be fully attributed to the oxidation of ingested fructose.

Sucrose and glucose

The ingestion of sucrose and glucose, in the same conditions of the ingestion of glucose and fructose (therefore, respectively 1.2 and 0.6 g/min, ratio 2:1, for total carbohydrate intake rate to 1.8 g/min), gives similar results.

Glucose, sucrose and fructose

Very high oxidation rates are found with a mixture of glucose, sucrose, and fructose (in the analyzed literature, respectively 1.2, 0.6 and 0.6 g/min, ratio 2:1:1, for total carbohydrate intake rate to 2.4 g/min; however, note the higher amounts of ingested carbohydrates).

Maltodextrin and fructose

Maltodextrin and Fructose: Oxidation of Ingested Carbohydrates
Fig. 1 – Oxidation of Ingested Carbohydrates

High oxidation rates are also observed with combinations of maltodextrin and fructose, in the same conditions of the ingestion of glucose plus fructose (therefore, respectively 1.2 and 0.6 g/min, ratio 2:1, for total carbohydrate intake rate to 1.8 g/min).

Such high oxidation rates can be achieved with carbohydrates ingested in a beverage, in a gel or in a low-fat, low protein, low-fiber energy bar.

The best combination of carbohydrates ingested during exercise seems to be the mixture of maltodextrin and fructose in a 2:1 ratio, in a 5% solution, and in a dose around 80-90 g/h.
Why?

  • This mixture has the best ratio between amount of ingested carbohydrates and their oxidation rate and it means that smaller amounts of carbohydrates remain in the stomach or gut reducing the risk of gastrointestinal complication/discomfort during prolonged exercise (see brackets grafa in the figure).
  • A solution containing a combination of multiple transportable carbohydrates and a carbohydrate content not exceeding 5% optimizes gastric emptying rate and improves fluid delivery.

Example of a 5% carbohydrate solution containing around 80-90 g of maltodextrin and fructose in a 2:1 rate; ingestion time around 1 h.

Conclusion

During prolonged exercise, when high exogenous carbohydrate oxidation rates are needed, the ingestion of multiple transportable carbohydrates is preferred above that of large amounts of a single carbohydrate.
The best mixture seems to be maltodextrin and fructose, in a 2:1 ratio, in a 5% concentration solution, and at ingestion rate of around 80-90 g/h.

References

Prolonged exercise and carbohydrate ingestion

Prolonged Exercise: Open Water Swimming
Fig. 1 – Open Water Swimming

During prolonged exercise (>90 min), like marathon, Ironman, cross-country skiing, road cycling or open water swimming, the effects of supplementary carbohydrates on performance are mainly metabolic rather than central and include:

  • the provision of an additional muscle fuel source when glycogen stores become depleted;
  • muscle glycogen sparing;
  • the prevention of low blood glucose concentrations.

How many carbohydrates should an athlete take?

The optimal amount of ingested carbohydrate is that which results in the maximal rate of exogenous carbohydrate oxidation without causing gastrointestinal discomfort”. (Jeukendrup A.E., 2008).

Prolonged exercise: which carbohydrates should an athlete take?

Until 2004 it was believed that carbohydrates ingested during exercise (also prolonged exercise) could be oxidized at a rate no higher than 1 g/min, that is, 60 g/h, independent of the type of carbohydrate.
Exogenous carbohydrate oxidation is limited by their intestinal absorption and the ingestion of more than around 60 g/min of a single type of carbohydrate will not increase carbohydrate oxidation rate but it is likely to be associated with gastrointestinal discomfort (see later).
Why?
At intestinal level, the passage of glucose (and galactose) is mediated by a sodium dependent transporter called SGLT1. This transporter becomes saturated at a carbohydrate intake about 60 g/h and this (and/or glucose disposal by the liver that regulates its transport into the bloodstream) limits the oxidation rate to 1g/min or 60 g/h. For this reason, also when glucose is ingested at very high rate (>60 g/h), exogenous carbohydrate oxidation rates higher 1.0-1.1 g/min are not observed.

The rate of oxidation of ingested maltose, sucrose, maltodextrins and glucose polymer is fairly similar to that of ingested glucose.

Fructose uses a different sodium independent transporter called GLUT5. Compared with glucose, fructose has, like galactose, a lower oxidation rate, probably due to its lower rate of intestinal absorption and the need to be converted into glucose in the liver, again like galactose, before it can be oxidized.

Prolonged Exercise: Maltodextrin and Fructose: Oxidation of Ingested Carbohydrates
Fig. 1 – Oxidation of Ingested Carbohydrates

However, if the athlete ingests different types of carbohydrates, which use different intestinal transporters, exogenous carbohydrate oxidation rate can increase significantly.
It seems that the best mixture is maltodextrins and fructose.

Note: the high rates of carbohydrate ingestion may be associated with delayed gastric emptying and fluid absorption; this can be minimized by ingesting combinations of multiple transportable carbohydrates that enhance fluid delivery compared with a single carbohydrate. This also causes relatively little gastrointestinal distress.

Conclusion

The ingestion of different types of carbohydrates that use different intestinal transporters can:

References

Carbohydrate ingestion during exercise of relatively short duration and high intensity

Intermittent high intensity exercise and carbohydrate ingestion

High Intensity: During-Exercise Nutrition
Fig. 1- During-Exercise Nutrition

Carbohydrate ingestion during intermittent high intensity or prolonged (>90 min) sub-maximal exercise can:

  • increase exercise capacity;
  • improve exercise performance;
  • postpone fatigue.

The intake of very small amounts of carbohydrates or carbohydrate mouth rinsing (for example with a 6% maltodextrin solution) may improve exercise performance by 2-3% when the exercise is of relatively short duration (<1 h) and high intensity (>75% VO2max), that is, an exercise not limited by the availability of muscle glycogen stores, given adequate diet.
The underlying mechanisms for the ergogenic effect of carbohydrates during this type of activity are not metabolic but may reside in the central nervous system: it seems that carbohydrates are detected in the oral cavity by unidentified receptors, promoting an enhanced sense of well-being and improving pacing.
These effects are independent of taste or sweet and non-sweet of carbohydrates but are specific to carbohydrates.

It should be noted that performance effects with drink ingestion are similar to the mouth rinse; therefore athletes, when they don’t complain of gastrointestinal distress when ingesting too much fluid, may have an advantage taking the drink (in endurance sports, dehydration and carbohydrate depletion are the most likely contributors to fatigue).

Conclusion

It seems that during exercise of relatively short duration (<1 h) and high intensity (>75% VO2max) it is not necessary to ingest large amounts of carbohydrates: a carbohydrate mouth rinsing or the intake of very small amounts of carbohydrates may be sufficient to obtain a performance benefit.

References

Hydration before endurance sports

Dehydration and endurance sports

Pre-hydration
Fig. 1 – Pre-hydration

In endurance sports, like Ironman, open water swimming, road cycling, marathon, or cross-country skiing, the most likely contributors to fatigue are dehydration and carbohydrate (especially liver and muscle glycogen) depletion.

Pre-hydration

Due to sweat loss needed to dissipate the heat generated during exercise, dehydration can compromise exercise performance.
It is important to start exercising in a euhydrated state, with normal plasma electrolyte levels, and attempt to maintain this state during any activity.
When an adequate amount of beverages with meals are consumed and a protracted recovery period (8-12 hours) has elapsed since the last exercise, the athlete should be euhydrated.
However, if s/he has not had adequate time or fluids/electrolytes volume to re-establish euhydration, a pre-hydration program may be useful to correct any previously incurred fluid-electrolyte deficit prior to initiating the next exercise.

Pre-hydration program

If during exercise the nutritional target is to reduce sweat loss to less than 2–3% of body weight, prior to exercise the athlete should drink beverages at least 4 hours before the start of the activity, for example, about 5-7 mL/kg body weight.
But if the urine is still dark (highly concentrated) and/or is minimal, s/he should slowly drink more beverages, for example, another 3-5 mL/kg body weight, about 2 hours before the start of activity so that urine output normalizes before starting the event.

It is advisable to consume small amounts of sodium-containing foods or salted snacks and/or beverages with sodium that help to stimulate thirst and retain the consumed fluids.
Moreover, palatability of the ingested beverages is important to promote fluid consumption before, during, and after exercise. Fluid palatability is influenced by several factors, such as:

  • temperature, often between 15 and 21 °C;
  • sodium content;
  • flavoring.

And hyper-hydration?

Hyper-hydration, especially in the heat, could improve thermoregulation and exercise performance, therefore, it might be useful for those who lose body water at high rates, as during exercise in hot conditions or who have difficulty drinking sufficient amounts of fluid during exercise.
However there are several risks:

  • fluids that expand the intra- and extra-cellular spaces (e.g. glycerol solutions plus water) greatly increase the risk of having to void during exercise;
  • hyper-hydration may dilute and lower plasma sodium which increases the risk of dilutional hyponatraemia, if during exercise, fluids are replaced aggressively.

Finally, it must be noted that plasma expanders or hyper-hydrating agents are banned by the World Anti-Doping Agency (WADA).

Conclusion

“Pre-hydrating with beverages, if needed, should be initiated at least several hours before the exercise task to enable fluid absorption and allow urine output to return toward normal levels. Consuming beverages with sodium and/or salted snacks or small meals with beverages can help stimulate thirst and retain needed fluids” (Sawka et al., 2007).

References

Ingestion of solid, liquid or gel carbohydrates 60 min before exercise

Liquid Carbohydrate Ingestion
Fig. 1 – Liquid Carbohydrate Ingestion

The form of carbohydrates ingested before exercise may have different effects on both metabolism and performance. Moreover, the ingestion of solid foods slows gastric empty, digestion and absorption rates compared with liquid foods and this has a different impact on glycemia.
For these reasons, several studies have investigated the effects of the form of carbohydrates on glycemic responses, oxidation rates and performance.

  • Studies comparing solid versus liquid carbohydrates and solid versus gel carbohydrates have found no difference in glycemic responses between groups.
  • Studies that have investigated difference in performance effects have found no differences.
  • Furthermore, no differences are found in carbohydrate oxidation rates between the carbohydrate ingestion in the three forms during exercise.

Therefore, it seems not to be the form of ingested carbohydrates that can enhance or reduce performance (in addition, even glycogen synthesis doesn’t vary; study conducted with liquid or solid carbohydrates).

Conclusion

It is advisable that athlete ingests whichever form of carbohydrates best suits, based on his experience and cost-effectiveness of the product.

References

Hypoglycemia and carbohydrate ingestion 60 min before exercise

Hypoglycemia: strategies to limit it in susceptible subjects

Hypoglycemia: Fatigue
Fig. 1 – Fatigue

From several studies it appears that the risk of developing hypoglycemia (blood glucose < 3.5 mmol /l or < 63 mg/l) is highly individual: some athletes are very prone to develop it and others are much more resistant.
A strategy to minimize glycemic and insulinemic responses during exercise is to delay carbohydrate ingestion just prior to exercise: in the last 5-15 min before exercise or during warm-up (even though followed by a short break).
Why?

  • Warm-up and then exercise increase catecholamine concentrations blunting insulin response.
  • Moreover, it has been shown that ingestion of carbohydrate-containing beverages during a warm-up (even if followed by a short break) does not lead to rebound hypoglycemia, independent of the amount of carbohydrates, but instead increases glycemia. When carbohydrates are ingested within 10 min before the onset of the exercise, exercise will start before the increase of insulin concentration.

Therefore, this timing strategy would provide carbohydrates minimizing the risk of a possible reactive hypoglycaemia.
In addition, it is possible to choose low glycemic index carbohydrates that lead to more stable glycemic and insulinemic responses during subsequent exercise.

Example: a 5-6% carbohydrate solution, often maltodextrin (i.e. 50-60 g maltodextrin in 1000 ml) or maltodextrin plus fructose (e.g. respectively 33 g plus 17 g in 1000 ml).

An intriguing observation is the lack of a clear relation between hypoglycaemia and its symptoms (likely related to a reduced delivery of glucose to the brain). In fact, symptoms are often reported in the absence of true hypoglycemia and hypoglycemia is not always associated with symptoms. Though the cause of the symptoms is still unknown, it is clearly not related to a glycemic threshold.

Conclusion

Some athletes develop symptoms similar to those of hypoglycemia, even though they aren’t always linked to actual low glycemia. To minimize these symptoms, for these subjects an individual approach is advisable. It may include:

  • carbohydrate ingestion just before the onset of exercise or during warm-up;
  • choose low-to-moderate GI carbohydrates that result in more stable glycemic and insulinemic responses;
  • or avoid carbohydrates 90 min before the onset of exercise.

References

Carbohydrate ingestion 60 min before exercise

Introductory statement

Carbohydrates
Fig. 1 – Carbohydrates

An high-carbohydrate diet in the days before exercise, as well as ingestion of meals high in carbohydrate 3-4 h before exercise, better if with low glycemic index, can have positive effects on athlete’s performance.

For many years it has been suggested that ingestion of carbohydrates 30-60 min before exercise may adversely affect performance because it could cause hypoglycemia (blood glucose < 3.5 mmol/l or < 63 mg/l), a major contributor to fatigue. In fact, a typical athlete’s mantra is: “Avoid carbohydrate in the hour before exercise”!
What is the reason of that?
Glucose ingestion may cause hyperglycaemia followed by hyperinsulinaemina that may result in:

  • a rapid decline in glycemia 15-30 minutes after the onset of exercise, called rebound or reactive hypoglycaemia, most likely the result of:

I. an increase in muscle glucose uptake (due to the mobilization of GLUT-4 transporters by the action of insulin but also from physical activity itself);
II. the reduction in liver glucose output;

  • in addition, higher availability of carbohydrates to the muscle stimulates glycolysis and this, in combination to insulin-induced inhibition of lipolysis in both adipose tissue and muscle, results in a reduction in fat oxidation (apparently long-chain fatty acids, not medium-chain fatty acids). This may lead to premature glycogen depletion and early onset of fatigue (glycogen would be almost the only available fuel for working muscle).
    This effect is temporary, approximately lasting only for the first 20 min of exercise so, it is likely that this little glycogen breakdown has no significant effect on exercise performance.

Therefore, at least in theory, carbohydrate ingestion 60 minutes before exercise could affect performance but only two studies (Foster et al. 1979, e Kovisto et al. 1981) have reported a reduced endurance capacity while the majority of studies have reported no change or an improvement in performance.
To clarify these results, a systematic series of studies was done in trained subjects. The conclusion of these studies was that:

  • There is no effect of pre-exercise carbohydrate feeding on performance, even though in some cases hypoglycaemia did develop”.
  • There was no relationship between low blood glucose concentrations and performance”. (Jeukendrup and Killer S.C. 2010)

Conclusion

Ingestion of meals rich in carbohydrates 3-4 h before exercise is important for the increase of liver and muscle glycogen stores, or for their resynthesis in previously depleted muscle and liver.
Carbohydrate ingestion 30-60 min before exercise may be important in topping-up liver glycogen stores which serve to maintain blood glucose concentrations during exercise.
Based on the currently available scientific evidences, there is no reason to avoid carbohydrates 60 min before the onset of exercise, because they don’t seem to have any detrimental effect on performance.

References

Carbohydrate loading before competition

Carbohydrate loading and endurance exercise

Carbohydrate loading: Alberto Sordi and Spaghetti
Fig. 1 – Alberto Sordi and Spaghetti

Carbohydrate loading is a good strategy to increase fuel stores in muscles before the start of the competition.

What does the muscle “eat” during endurance exercise?

Muscle “eats” carbohydrates, in the form of glycogen, stored in the muscles and liver, carbohydrates ingested during the exercise or just before that, and fat.

During endurance exercise, the most likely contributors to fatigue are dehydration and carbohydrate depletion, especially of muscle and liver glycogen.
To prevent the “crisis” due to the depletion of muscle and liver carbohydrates, it is essential having high glycogen stores before the start of the activity.

What does affect glycogen stores?

  • The diet in the days before the competition.
  • The level of training (well-trained athletes synthesize more glycogen and have potentially higher stores, because they have more efficient enzymes).
  • The activity in the day of the competition and the days before (if muscle doesn’t work it doesn’t lose glycogen). Therefore, it is better to do light trainings in the days before the competition, not to deplete glycogen stores, and to take care of nutrition.

The “Swedish origin” of carbohydrate loading

Very high muscle glycogen levels (the so-called glycogen supercompensation) can improve performance, i.e. time to complete a predetermined distance, by 2-3% in the events lasting more than 90 minutes, compared with low to normal glycogen, while benefits seem to be little or absent when the duration of the event is less than 90 min.
Well-trained athletes can achieve glycogen supercompensation without the depletion phase prior to carbohydrate loading, the old technique discovered by two Swedish researchers, Saltin and Hermansen, in 1960s.
The researchers discovered that muscle glycogen concentration could be doubled in the six days before the competition following this diet:

  • three days of low carb menu (a nutritional plan very poor in carbohydrates, i.e. without pasta, rice, bread, potatoes, legumes, fruits etc.);
  • three days of high carbohydrate diet, the so-called carbohydrate loading (a nutritional plan very rich in carbohydrates).

This diet causes a lot of problems: the first three days are very hard and there may be symptoms similar to depression due to low glucose delivery to brain, and the benefits are few.
Moreover, with the current training techniques, the type and amount of work done, we can indeed obtain high levels of glycogen: above 2.5 g/kg of body weight.

The “corrent” carbohydrate loading

Carbohydrate Loading
Fig. 2 – Carbohydrate Loading: 2500 kcal Diet

If we compete on Sunday, a possible training/nutritional plan to obtain supercompensation of glycogen stores can be the following:

  • Wednesday, namely four days before the competition, moderate training and then dinner without carbohydrates;
  • from Thursday on, namely the three days before the competition, hyperglucidic diet and light trainings.

The amount of dietary carbohydrates needed to recover glycogen stores or to promote glycogen loading depends on the duration and intensity of the training programme, and they span from 5 to 12 g/kg of body weight/d, depending on the athlete and his activity. With higher carbohydrate intake you can achieve higher glycogen stores but this does not always results in better performance; moreover, it should be noted that glycogen storage is associated with weight gain due to water retention (approximately 3 g per gram of glycogen), and this may not be desirable in some sports.

References