In this section we will see how a post-workout recovery meal should be properly set up.

Metabolism after training

  Training, of course, implies a depletion of the body’s energy reserves. Precisely for this reason, whenever a muscle or muscle group is subjected to substantial exertion, it immediately sets itself up to recover lost energy and, as a result, causes GLUT-4 to be shifted from the inside of the cells, to the membrane. It should be noted that cell sensitivity to insulin is rarely 100%: some of the GLUT-4, even in the best of cases, remains inside the cell and is never moved to the surface. The time when the sensitivity of muscle fibres to insulin is closest to its maximum is precisely the period immediately following exercise, especially if at high intensity.

The anabolic window theory

  In the period immediately following exercise, therefore, cell metabolism is very different from what it is at other times of the day. Muscle cells are particularly prone to absorb glucose and other nutrients from the blood, while the amount of the latter that is converted into fatty acids and deposited in the adipocytes is minimal. Raising insulin levels during this period does not mean gaining weight, but rather feeding the muscles. The period of time during which the metabolism remains in this condition is called the ‘anabolic window’. It lasts about thirty minutes after the end of physical exertion, but a situation that most athletes would consider metabolically more convenient than normal remains for a further one to two and a half hours.

Post-workout nutrition

  Let’s now see what and how much to eat after training.

What to eat during the anabolic window

  We must not forget that there is one hormone whose blood levels at the end of exercise can be quite high: cortisol. As we have discovered, cortisol tends to raise blood sugar levels because it stimulates hepatic gluconeogenesis. On the other hand, consuming carbohydrate foods in the anabolic window means increasing the secretion of insulin, a hormone that seeks to reduce glycaemia, and therefore antagonistic to cortisol. The two hormones consequently enter into competition. Two different situations can take place at this point:

1. insulin gets the better of cortisol in a short time. The levels of the latter are lowered following the recovery meal, the cells are nourished and no weight is gained;
2. insulin cannot get the better of cortisol, the endocrine pancreas secretes more insulin and the cells develop resistance to it. As a result, one does not recover adequately from exertion and gains weight.

Consuming protein-based foods would have less of an impact on insulinemia than a carbohydrate-based meal, but what it would cause, however small, is no different. As for fats, if one intends to lose weight, these should be avoided completely in the anabolic window: during this time, in fact, the body is predisposed to accumulate reserves to restore the energy it has lost during exercise, certainly not to burn more. This is why consuming fat after exercise will easily lead to gaining weight. It is a different matter, of course, for athletes who do not fear or even desire an increase in fat mass. Which of the two above-mentioned scenarios will occur is impossible to know beforehand. One has to experiment to try to work out whether and what to eat during the anabolic window. The options are as follows:

1. consume only high-GI carbohydrates;
2. consume only medium-GI carbohydrates;
3. consume only low-GI carbohydrates;
4. consume only protein;
5. variously mix the above nutrients;
6. not eating at all (wait thirty minutes to two hours before eating a meal).

A starting point for experimentation could be the following:

• if the training was not very intense and very voluminous, i.e., relatively long, continuous and without breaks (e.g. an hour of running), consume carbohydrates and protein in a ratio of 4:1 in favour of the former, with half of the carbohydrates having a high glycaemic index and the other half a low glycaemic index;
• if the workout was moderately intense and voluminous, i.e. moderately long and with relatively short breaks (e.g. a series of 30sec. sprints, interspersed with 45sec. recovery), consume carbohydrates and protein in a 3:1 ratio in favour of carbohydrates, with half of the latter being high GI and the other half low GI;
• if the training you have just completed was high-intensity, with very long breaks (for example, a weight-lifting session for strength), consume carbohydrates and protein in a ratio of 2:1 in favour of the former, with half high-glycaemic-index carbohydrates and the other half low-glycaemic-index.

There are products on the market, called gainers, which already mix proteins and carbohydrates. Such products (regardless of whether they are bought ready-made or prepared yourself) increase the amount of protein that is absorbed in the intestines, as the carbohydrates taken in at the same time slow down their digestion and thus reduce the amount destroyed during digestion. In the search for your ideal solution, however, it is worth bearing in mind that the effect of carbohydrates on recovery is not only linked to their trophic function on the cells, but also to their ability to reduce the amount of cytokines produced during loading. Cytokines, in fact, are particular cells of the immune system that can damage muscle tissue, and if their quantity is limited, recovery is enhanced.

How much to eat during the anabolic window

  The amount of carbohydrates and/or protein consumed during the anabolic window is another parameter that can influence the insulin/cortisol balance mentioned in the previous paragraph. The more one consumes, the more insulin will tend to increase. Once again, therefore, it is not possible to give precise indications. You have to experiment and try to work out what works best. In fact, each athlete is different. However, it is possible to make some suggestions: if you are on a non-ketogenic diet, an excess of carbohydrates could lead to reactive hypoglycaemia, so it may not be a good idea to overdo it; if, on the other hand, you are on a ketogenic diet, I suggest that you keep those few carbohydrates that you should consume over a twenty-four-hour period just for this moment. Furthermore, as the anabolic window is the time of day when the body is least likely to put on weight, it would make sense to try to introduce as many calories as possible of the daily quota required by the diet during this time. In the case of a non-ketogenic diet, a starting point for experimenting, referring to the examples on carbohydrate/protein ratios given earlier, could be one gram of carbohydrate per kilogram of lean body mass. Protein should then be calculated accordingly. If, for example, one has a lean body mass of 62 kg and the training performed was of medium intensity and medium volume one should consume 31g (62 : 2 = 31) of high glycaemic index carbohydrates, 31g of low glycaemic index carbohydrates and 21g (62 : 3 ≈ 21) of protein.

Rehydration

It is obvious that training, especially conditioning training, involves muscular effort. Now, muscle contraction produces heat, and since the human body, in order to be perfectly healthy, must maintain its body temperature within a certain range (which, as we have seen several times, fluctuates slightly around 37 °C), it must implement procedures to prevent the heat produced by muscle contraction from accumulating too much. This procedure consists of the production and excretion of sweat through the skin (in this case, through the 2-4 million sweat glands present on the skin’s surface). The heat, “trapped” inside the sweat, is thus eliminated. However, sweat production has two major side effects:

1. dehydration, or loss of water;
2. loss of mineral salts.

More specifically, the mineral salts that are lost are electrolytes, i.e., chemical compounds that, when broken down into their elements, give rise to the formation of ions (particles with electric charges). The following electrolytes are present in sweat:

1. sodium: 805 mg/l (but can vary between 230 and 1609 mg/l);
2. Chlorine: 177-2127 (average 1152) mg/l;
3. Potassium: 195 mg/l (but can vary between 39 and 586 mg/l);
4. Magnesium: 32 mg/l.

Characteristics of workouts requiring rehydration and salt replenishment

We have already discovered that water and the aforementioned electrolytes are extremely important for maintaining good health. This is why, whenever you undergo training that involves profuse sweating, and therefore an equally abundant loss of water and minerals, replenishment must take place as soon as possible. Workouts that usually require rehydration strategies are those focused on endurance, as they place more stress than others on the body’s mechanisms involved in maintaining body temperature (thermoregulation) and therefore cause significant sweating. Despite this, some people may tend to sweat profusely during other types of training. In this case, the application of a replenishment strategy is certainly necessary.

Rehydration drinks

Rehydration drinks are used to replenish nutrients lost during training. These drinks are designed to maximize the rehydration process and minimize unwanted side effects. These characteristics consist primarily of appropriate osmolarity, i.e., the ratio between the solvent and everything dissolved in it, and secondly, the ratio between the various solutes, as well as the appropriate temperature. In addition to all this, since, as mentioned, a lot of water is lost through sweat, it is essential that the drink provides a substantial supply of this nutrient. The ideal solvent is therefore water. Finally, it should be noted that a meal that restores energy sources and leads to the early elimination of fatigue waste can also facilitate rehydration. In order to better navigate the wide range of products on the market that are specifically designed for rehydration, from ready-made drinks to powdered electrolytes to be added to water, this section will explore the characteristics of an effective rehydration drink.

The osmolarity of rehydration drinks

In order for rehydration to take place optimally and with few side effects, the drink consumed must have an appropriate osmolarity. The benchmark is blood plasma, i.e., the liquid part of blood, whose osmolarity is between 275 mOsm/l and 295 mOsm/l. Drinks can therefore be classified into three different groups based on their osmolarity compared to that of plasma:

• Hypotonic: drinks whose osmolarity is lower than that of plasma.
• Isotonic: drinks with the same osmolarity as plasma.
• Hypertonic: drinks with a higher osmolarity than plasma.

In order to understand why one of these three solutions is preferable to the others, it is necessary to introduce the chemical concept of osmosis: imagine a container divided into two compartments by a semi-permeable barrier. If a solvent capable of passing through the barrier is poured into the two compartments in a balanced manner and then any solutes that are unable to pass from one compartment to the other are added, so that there is a greater quantity in one of the two, the solvent will spontaneously (i.e., without the need for energy consumption) move from the compartment where there are fewer solutes to the one where there are more until the concentration levels are equal. Now, imagine transposing this situation to the biological context of the digestive system: the first compartment is the intestinal lumen, the second is the bloodstream, the barrier is the intestinal wall, and the solvents are, on the one hand, plasma and, on the other, the liquid of the beverage consumed (which is usually water). If the solutes dissolved in the drink are so abundant that their concentration is higher than that of the particles in the plasma (osmolarity of the drink higher than that of the plasma), what will happen, as seen above, is a shift of blood fluids into the intestinal lumen, so that the concentration of solutes in the intestinal lumen equals that of the particles in the plasma. The result will be further dehydration. Of course, this is a temporary phenomenon: in fact, within a relatively short period of time, the entire beverage will pass through the intestinal walls and enter the bloodstream. Nevertheless, dehydration will still occur as a result of drinking the beverage. This is the main reason why it is advisable to avoid drinking hypertonic beverages when dehydrated. Another reason is that if the hypertonic drink is consumed during training, it could lead to intestinal disorders. Let’s now consider the opposite situation, in which mineral water (a hypotonic drink) is consumed. In this circumstance, two different scenarios are possible: in the first, since the rate of urine production is directly proportional to water intake, it may happen that the rate at which the body removes water from the blood for this purpose is higher than the rate at which it absorbs it in the digestive system. In this circumstance, water consumption could lead, as in the case of hypertonic drinks, to temporary mild dehydration. In the second scenario, however, the amount of water in the blood actually increases, but precisely for this reason, the concentration of particles in the plasma, already reduced as a result of the loss of electrolytes through sweat, will drop sharply. This will lead to a condition called hyponatremia (low sodium levels in the blood), also known as “water intoxication.” And although the name should not cause too much alarm (such a situation caused by excessive water consumption certainly does not pose serious health risks), it is definitely a situation to be avoided. Furthermore, when hyponatremia is about to set in, the body blocks the thirst stimulus, so you are inclined to stop drinking fluids (even though your body still needs them). In conclusion, therefore, in both scenarios, the replenishment of lost nutrients will be far from optimal. The problems associated with drinking a hypotonic beverage, as well as those caused by a hypertonic beverage, can be avoided if its osmolarity is brought back to that of plasma. Nevertheless, even this solution is imperfect: sweat is hypotonic. For this reason, consuming an isotonic drink means consuming too many minerals and too little water compared to what has been lost through sweating during training. A drink with full rehydrating power is therefore to be considered by the average athlete as an ideal that can be approached but is difficult to achieve. As a general guideline, we can say that isotonic or slightly hypotonic drinks work best for most athletes.

The proportion between solutes

For optimal rehydration, the osmolarity of the solution is not the only thing that matters. It is also important that the solutes present in the drink are in the right proportions, i.e., those found in sweat. It is also necessary to maintain a certain balance between sodium and potassium intake. Although Weschler (2006) shows that there is an inverse correlation between athletic performance and the rate at which blood sodium concentration decreases, indiscriminate sodium intake will lead to accelerated potassium excretion through urine (Schirreffs, 1998). In doing so, while blood sodium reserves will be restored, potassium reserves will be further depleted. Unfortunately, it is not possible to establish a universally valid amount for sodium and potassium supplementation in rehydration drinks, as the values for optimal balance differ between individuals, but it is certainly worth considering the recommendation to maintain the amount of sodium between 400 and 700mg per liter of drink. For a highly detailed study (which may be excessive for the average athlete), it will therefore be necessary to start from the quantities of each electrolyte present in sweat and then attempt experiments in which the balance between sodium and potassium is modified, with the specific recommendation never to exceed the recommended upper limit for sodium, and see if there are any repercussions on performance. The result of each experiment will provide useful feedback for setting up subsequent experiments. For example, if in an initial experiment you try to consume an amount of sodium close to the upper limit and find that your performance deteriorates due to dehydration, in the next experiment you can try a lower amount. If the result is still unsatisfactory, you could then try an amount of sodium that is intermediate between those used in the two previous experiments. Now, as mentioned above, sweat contains:

1. sodium: between 230 and 1609 mg/l (mode, i.e., most frequently found value, 805 mg/l);
2. chlorine: between 177 and 2127 mg/l;
3. potassium: between 39 and 586 mg/l (mode 195 mg/l);
4. magnesium: 32 mg/l.

So, using the modal value where available and the average value in the absence of a mode:

∑ Electrolytes in sweat = 805 + 1152 + 195 + 32

∑ Electrolytes in sweat = 2184

At this point, the percentage of each electrolyte relative to 2184 (mg/l) can be calculated:

So:

The percentages (indicative and by no means to be taken as absolute) of each electrolyte in solution must therefore be:

• sodium = 36,86%
• chlorine = 52,75%
• potassium = 8,93%
• magnesium = 1,46%

The temperature of the rehydration drink

It has been proven that when physical exertion is applied in a very hot environment, drinking a chilled beverage at a temperature of around 4°C improves the quality of recovery.

Preparing a rehydration drink in practice

If you want to prepare your own rehydration drink, the main difficulty in formulating a highly effective one is calculating the quantity of solvent in relation to that of solutes (given a priori) or vice versa (with the quantity of solvent given a priori) in order to optimize osmolarity. Succeeding in this task while also maintaining the correct proportion of electrolytes can mean exceeding, even significantly, the maximum sodium value established. Often, ready-made rehydration products on the market consist of compromises between optimal osmolarity, sodium quantity, and solute proportion, with different manufacturers offering different solutions. Sometimes, not only to overcome this problem, other ingredients with a nutritional function are added. When added in the right quantities, these ingredients allow osmolarity to be optimized while keeping sodium within safe limits and in the right proportions with other electrolytes. Later on, we will discuss in detail how to enrich rehydration drinks with nutrients other than electrolytes, but for now, for purely educational purposes, we will ignore the issue of maximum sodium intake limits. Now, regardless of whether the amount of solutes or solvent is given a priori together with osmolarity (remember that osmolarity must be determined based on that of plasma), before proceeding with the calculations, we must consider a specific characteristic of solutes: atomic weight. This parameter indicates the mass of an atom of a particular element. Its value differs depending on the element. Data on the atomic weight of specific elements can be easily found by consulting the periodic table of elements (or by searching for them on Google), but to provide further assistance, those relevant to the preparation of the rehydration drink are listed below (the unit of measurement is grams per mole, g/mol):

1. Sodium (Na): 22.99 g/mol
2. Chlorine (Cl): 35.45 g/mol
3. Potassium (K): 39.1 g/mol
4. Magnesium (Mg): 24.3 g/mol

Now, if you want to calculate the volume of the solution based on the amount of solutes, if the osmolarity of the rehydration drink is equal to:

So:

For example, let’s say we want to prepare a rehydrating drink with an osmolarity of 275 mOsm/l, using low-mineral content water as a solvent and a supplement that contains, in 1g of product, all and only the mineral salts to be replenished in the following quantities (the proportions between the electrolytes are obviously correct):

• Sodium: 296 mg
• Chlorine: 424 mg
• Potassium: 72 mg
• Magnesium: 8 mg

Approximating the volume of the entire solution to that of the low-mineral content water alone, the volume of the latter for each gram of supplement will be equal to:

Water = 100 ml per gram of product

The alternative calculation method involves calculating the total amount of solutes based on the volume of the solution. Following this method, the various ratios between the amount of each electrolyte contained in the supplement dose (indicated on the label or established arbitrarily) and the corresponding atomic weight (the value is expressed in millimoles, mmol) are first calculated, and then the results obtained are added together.

Subsequently, in order to obtain the total millimoles of solutes to be dissolved in the designated amount of solvent, the desired osmolarity is multiplied by the volume of the solution (or, by approximation, of the solvent alone).

Total millimoles in rehydration drink = osmolarity × solution volume

To calculate the amount of supplement to add to the solvent, multiply the total millimoles that must be present in the rehydration drink by the amount of supplement in a single dose; then divide the result by the total millimoles present in a single dose:

Let’s look at an example: suppose you want to make a drink with an osmolarity of 275 mOsm/l, with a volume of 2 l (the volume of the solution is approximated to that of the solvent), using the supplement mentioned in the previous example. First, calculate the total millimoles in the dose:

Total millimoles in the dose = 27 mmol

Then calculate the total millimoles that must be in the drink:

Total millimoles in rehydration drink = 275 × 2

Total millimoles in rehydration drink = 550 mmol

Finally, calculate the amount of supplement to be dissolved in 2 liters of solvent:

Supplement to assume ~ 20 mg

Amount of rehydration drink to consume

It is recommended to consume a quantity of rehydration drink, expressed in liters, equal to the kilograms of body weight lost during training (mostly due to sweating). In this regard, if you expect to sweat profusely during your training session, it is advisable to weigh yourself both before and after the session and then calculate the difference.

Enriching the rehydration drink

As already explained, it is of paramount importance that the replenishment of nutrients covers everything that is lost through sweat, but it is also possible to enhance the rehydration drink with other elements, provided that the osmolarity does not vary and that the quantities of chloride, sodium, potassium, and magnesium are not depleted too much to make room for them. In this case, you can consider enriching the drink with calcium, sugars, proteins, and amino acids. The first is a mineral that is very important for muscle contraction, and a deficiency can cause cramps. And while calcium is not excreted in significant quantities through sweat, muscle contraction involves a physiological breakdown of muscle fibers with invasion by calcium ions from the extracellular environment. It goes without saying that the calcium lost in this way must be replenished. Taking calcium, especially if further training is planned during the day, can help prevent muscle cramps. In order to calculate the total amount of solutes, it is necessary to know that the molar mass of calcium is 40.078 g/mol (Van’t Hoff coefficient equal to 1, i.e., negligible). It is recommended not to exceed 10-11% of total electrolytes. The percentage of each electrolyte (again, only indicative), adding calcium, should therefore be:

• sodium = 33.17%
• chlorine = 47.48%
• potassium = 8.04%
• magnesium = 1.31%
• calcium = 10%

As for sugars, in addition to having the same function as in post-workout recovery meals, when added at a concentration of 6%, they can facilitate hydration by accelerating fluid absorption. On the contrary, too high a concentration can lead to either a loss of the drink’s optimal osmolarity or an electrolyte intake that is lower than the body’s needs. Furthermore, if the drink is consumed during training rather than after, a drink that is too rich in sugars could cause intestinal disorders (the topic of nutrition during training will be discussed in more detail later). As far as the choice of sugar is concerned, those with a high glycemic index are particularly suitable. More specifically, sucrose (common sugar, consisting of glucose and fructose) or glucose are recommended. The molar mass of sucrose (table sugar) is 342.3 g/mol, while that of glucose is 180.156 g/mol. In both cases, the Van’t Hoff coefficient is 1, so it is not to be considered. If sugars are added to the drink to optimize osmolarity while respecting the proportions between mineral salts and the sodium limit, then it may be necessary to use a mixture of glucose and sucrose. More specifically, if the amount of sodium is reduced to maintain its optimal value and the amounts of other electrolytes are also reduced accordingly to maintain their proportions, then it will be necessary to recover the millimoles lost in these operations by adding other solutes. If these solutes are sugars, as mentioned, their quantity must be 6 g per 100 ml of beverage, so in order for the osmolarity calculation to give the desired result, the sugars chosen must have the right molecular weight (the molecular weight is the sum of the atomic weights of all the atoms that make up the molecule). It is therefore necessary to use the molecules most suitable for the specific case. For example, assuming you want to make a drink containing 500 mg of sodium in one liter, the quantities of electrolytes in one liter of solution should be as follows (assuming that no calcium or anything else is added):

• sodium: 500 mg
• chlorine: 715 mg
• potassium: 121 mg
• magnesium: 20 mg

For these quantities, the osmolarity is equal to:

Osmolarity = 45,81

Such a drink would be too hypotonic, so sugar needs to be added to achieve a target of, say, 275 mOsm. If this sugar is to be added in quantities of 6 g per 100 ml of drink (or 60 g per liter, which is the same), then:

Molecular mass of sugars ~ 262

This molecular mass can be achieved by mixing glucose and sucrose (the total amount of sugars must still be equal to 60 g per liter of beverage). More specifically, considering that the residual osmolarity is equal to 229.19 (275 – 45.81 = 229.19), then:

Considering also that the amount of sucrose must be equal to 60 g minus the amount of glucose, we can write:

By solving the equation, we can conclude that the glucose to be added to the solution should be approximately 20 g, while sucrose should make up the remaining 40 g of the total sugars. As for proteins and amino acids, these molecules have an exclusively nutritional function. The former have already been discussed above on this page, and further information can be found on the following pages:

• Proteins
• Soluble proteins

Further information on amino acids can be found on the following pages:

• Amino acids
• Branched-chain amino acids

With regard to the influence of proteins and amino acids on osmolarity, only the latter have a significant effect. Proteins, in fact, as macropeptides (i.e., very large molecules), have an enormous molecular mass compared to that of other solutes. This implies a negligible influence on osmolarity. However, those who choose to prepare their own rehydration drink by adding soluble proteins should pay attention to the ingredients listed on the label. Often, in fact, it is the other nutrients in the product, even if present only in small amounts, that influence osmolarity more than the protein molecules. To calculate osmolarity, I list below the molecular mass of the 20 proteinogenic amino acids (i.e., those that contribute to the formation of proteins):

Amino acid	Molecular mass
Alanine	89.09 g/mol
Arginine	174.2 g/mol
Asparagine	132.12 g/mol
Aspartic acid	133.1 g/mol
Cysteine	121.16 g/mol
Phenylalanine	165.19 g/mol
Glutamine	146.14 g/mol
Glutamic acid	147.13 g/mol
Glycine	75.07 g/mol
Histidine	155.15 g/mol
Isoleucine	131.17 g/mol
Leucine	131.17 g/mol
Lysine	146.19 g/mol
Methionine	149.21 g/mol
Proline	115.13 g/mol
Serine	105.09 g/mol
Threonine	119.12 g/mol
Tryptophan	204.23 g/mol
Tyrosine	181.19 g/mol
Valine	117.15 g/mol