By Martin LaSalle 

Expenses of the body on effort

Sporting activity involves two types of expenditure for the body: energy and water.

Energy expenditure. A person who trains or participates in a sport can expend up to three times as much energy as a person at rest. Its diet is therefore of paramount importance since it provides it, among other things, with three energy nutrients: proteins, carbohydrates and lipids.

These are – by far – the carbohydrates that provide the most energy to the athlete: they represent 50 to 60% of the total energy intake required by the body in activity. The lipid requirements are of the order of 15 to 25% and those in proteins oscillate between 15 and 20%. (These proportions may vary from one individual to another and depending on the sport practiced.)

In general, when training intensively, the body mainly uses carbohydrates as an energy base. Conversely, if the training is moderate and lasts longer, the body will use more fat reserves (lipids). But beware: this is not a question of weight loss, but of energy expenditure.

It goes without saying that energy needs vary from one individual to another, in addition to depending on the type of exercise practiced, its intensity and its duration.

Water expenditure. Physical exercise causes a significant production of heat, therefore an increase in body temperature.

To avoid overheating, the body therefore dissipates excess heat especially through sweat, which is composed of 99% water and 1% salt. Sweating alone is responsible for over 80% of body fluid loss during training.

Two to three liters of water can be lost through the evaporation of sweat during prolonged exercise. Since the blood – like the whole body for that matter – is made up of 70% water, water loss decreases the amount of blood in the body and slows down the transport of energy to the muscle. In addition, the loss of water disrupts the thermoregulation of the body: less water means less sweat, therefore slower heat dissipation.

This is why dehydration threatens the athlete who neglects to drink enough. Ultimately, if the athlete continues to “push the machine” without hydrating, their body will reduce sweat production to conserve water reserves. Her body temperature will rise, and if it rises above 41 degrees Celsius, it will be heatstroke.

Physiological needs before exercise

When and what to eat It has been scientifically shown that performance is better when physical activity is preceded by a meal than when it is done on an empty stomach. Nevertheless, comfort requires, it is better to avoid that the digestive system is in full work during the sporting activity. It is therefore best to eat three to four hours before the activity. Fats (lipids) take six to nine hours to be digested, so they need to be consumed even longer in advance.

Muscles during exertion mainly need carbohydrates. To fill up with these nutrients, choose cereal foods that contain a large number of them and are more easily absorbed by the body: pasta made from whole wheat, rice cakes, semolina, bread, weak granola bars. in bold, etc. If you have less than two hours, you will opt for fruits, a mixture of nuts and dried fruits as well as fruit or vegetable juices, which contain carbohydrates that are more quickly assimilated by the body.

Fats – or lipids – occupy an important place in the diet of the athlete, because they provide energy, liposoluble vitamins (that is to say soluble in fats, such as vitamins A, D and E ), as well as essential fatty acids. Fat intake should not be less than 15% of overall energy.

Protein requirements as an energy source are significantly lower: they represent around 2% of energy intake. Because they take more or less four hours to be digested, their role will consist above all in reducing hunger during exercise.

As pointed out by the Coaching Association of Canada², a meal or snack before exercise should, in general:

• provide enough fluids to ensure hydration;
• be low in fat and fiber to facilitate gastric emptying and reduce gastrointestinal discomfort;
• be rich in carbohydrates to maintain blood glucose levels;
• have a moderate protein content;
• be composed of familiar and well-tolerated foods.

We must also insist on this last point: individual needs differ from one person to another and it is up to the athlete to find what suits him best to optimize his performance.

When and what to drink Two hours before exercise, athletes should take 400 to 600 ml (14 to 22 ounces) of water, juice or energy drink containing between 4 and 8% carbohydrate. Then, 10 minutes before, it is recommended to drink again between 125 and 250 ml.

Warm up gently. The role of the warm-up is to generate heat to increase the efficiency of chemical reactions in the muscle cells and to dilate the blood vessels which can thus allow more blood to flow to the muscles.

Likewise, warming up prevents muscle injury, since warmed up muscle is up to 20% more flexible than when it is “cold”.

Another important advantage of warming up is that it gradually prepares the heart to cope with sustained efforts.

Warming up is the opposite of exhausting yourself. This is why strenuous efforts – such as sit-ups, push up (or crunches) and sprints – are not considered warm-up exercises.

Rather, go slowly, opting for a combination of light exercise that will gradually raise the blood pulse and body temperature: hopping in place, cycling at low speed, performing jumps with simultaneous lateral separation of the arms and legs. legs (Jumping Jack), trotting, etc.

The duration of the warm-up depends on the duration and intensity of the activity that will follow.

Stretching: be careful! Researches¹ tend to show that stretching done immediately before exercise has no effect on injury prevention. In addition, they decrease certain types of performance, such as jumping.

It is important here to distinguish between cold stretches and those that are practiced regularly.

It is therefore strongly discouraged to perform sudden and overly pronounced stretches without prior warm-up, as they could damage the muscles and tendons instead of preparing them to function better.

In addition, like physical exercise performed on a regular basis, stretching sessions performed over several weeks could improve performance and prevent injury, according to some scientists.

Needs during exercise

Consuming nutrients during exercise is aimed at replacing fluid loss and providing enough carbohydrate to maintain blood glucose levels.

This is all the more important if one carries out an endurance activity which takes place in extreme conditions (heat, cold or altitude).

As a rule, it is not necessary to drink during a exercise of less than 30 minutes. Moreover, for an effort that will stretch 30 to 60 minutes, drink 125 to 250 ml of fluid every 15 to 20 minutes. In hot, humid weather, it is best to start drinking as soon as you start to exercise and then drink more frequently as needed.

During a sporting activity that lasts more than 60 minutes, do not wait until you are thirsty to drink. The absorption of liquid will allow both to hydrate, to stock up on sugar and to compensate for the loss of mineral salts evacuated by sweat. To do this, you can use slightly sweetened water containing a certain amount of salt, or even a sweet drink. In this regard, it is better to look for drinks with less than 100 grams of sugar per liter, so that the digestive system absorbs it faster.

The hiking marathoners and cyclists will be able to replenish your energy by consuming bars, fruits or their juice, also in small quantities and at a regular frequency.

To avoid stomach cramps, avoid anything that contains gas: during training, the stomach is hot and the gas in it expands. They then create pressure. In addition, a liquid that is too cold can also cause cramps, since under the action of the cold, the stomach contracts. A cool liquid is preferred.

It is important to indicate that during a medium or long effort, there is no “one rule” as to water and energy needs. In such circumstances, you should drink according to your own water and energy losses, as well as according to your own tastes.

Needs after exercise

What to eat and how much? After exercise, sufficient energy and carbohydrate should be provided to restore muscle glycogen and ensure rapid recovery of the muscles. If exercise has depleted glycogen stores, a carbohydrate intake of 1,5 g / kg of body weight for the first 30 minutes and then every two hours for four to six hours will be enough to restore them.².

Indeed, during the first 30 minutes after prolonged exercise, the body seeks to replenish its reserves as quickly as possible and to regenerate itself. Insulin – an anabolic hormone that brings glucose from the blood into cells – is then “out of stock” and asks only to quickly gather carbohydrates and proteins.

Some products that can fill nutritional and energy deficits include fruit yogurts, cereals, bananas, vegetable juices, crackers, cheeses, energy bars and drinks.

What to drink and in what quantity? To compensate for the water and salt deficit caused by prolonged activity, it may be necessary to drink up to 1,5 liters of fluid for every pound of body weight lost after physical activity. A sugary drink will meet these needs and allow the athlete to replenish his glycogen reserves. Drinks containing caffeine as well as alcoholic or carbonated drinks should be avoided. To know if you have drunk enough, you can rely on the color of your urine: if it has become clear again, the hydration is finished.

Stretch carefully. Post-workout stretches are known to have a beneficial effect on muscles and tendons, but scientific evidence is yet to be demonstrated in this regard. It is generally believed that stretching done on a regular basis will strengthen muscles and ultimately improve performance.

Cool down. When finishing physical activity, it is best to slow down the body activity for a few minutes by walking and breathing deeply. This accelerates the evacuation of lactic acid accumulated in the muscles, while soothing the cardiovascular system.

We would like to thank Ms. Marielle Ledoux, professor in the Department of Nutrition at the University of Montreal, for her judicious advice and clarifications.