Biochemical Foundations of Human Vital Activity - Volkov, N.I., Nesen, E.N. 2000

Biochemistry of Sports
Biochemical Foundations of Rational Nutrition for Athletes
Energy Consumption of the Organism and Its Dependence on the Performed Work

A balanced diet involves maintaining an Energy balance in the body based on the following principle: The amount of energy intake must correspond to the amount of energy expended.

Energy enters The Human Body with food in the form of CARBOHYDRATES, fats, and Proteins. Within the body's Cells, during chemical transformations, this energy is extracted and utilized for various physiological needs. As is well known, The oxidation of 1 g of carbohydrates or proteins yields 4 kcal (17 kJ) of energy, whereas fats yield 9 kcal (37 kJ). By knowing the Chemical Composition and caloric value of food products from specialized tables, one can calculate the caloric content of any menu or diet. Typically, the caloric value or energy content of foods is expressed in kilocalories per 100 g of the product or per recommended serving size (Table 40).

A person's daily caloric requirement varies depending on Energy Expenditure (Table 41). During short-term energy deficits (low caloric intake), the body draws upon its energy reserves—primarily fats and complex carbohydrates. In cases of prolonged deprivation, however, not only fats and carbohydrates but also proteins are broken down, leading to weight loss, Muscle atrophy, anemia, growth retardation, and reduced physical performance. Conversely, an excess of energy intake diminishes its utilization, causing surplus carbohydrates and fats to be stored in Tissues as adipose tissue, which can lead to obesity.

Class="center">TABLE 40 Caloric Value of Selected Foods

Total daily energy expenditure in humans includes basal metabolic rate (the minimum amount of energy required to sustain vital body Functions and biosynthetic processes at relative rest), the specific dynamic action of food—namely, the energy expended on Digestion AND ABSORPTION (averaging 10–15% of total daily energy expenditure on a mixed diet)—as well as energy expended during various types of physical and mental activity.

Basal metabolic rate depends on age, gender, body mass, environmental conditions, and individual traits. For an adult male weighing 65 kg, it averages 1600–1800 kcal, whereas for a female weighing 55 kg, it is 1300–1400 kcal. In children, calculated per unit of body mass, the basal metabolic rate is 1.5 times higher than in adults, while in elderly individuals it is lower than in adults.

The specific dynamic action of food varies in energy expenditure depending on the proportion of proteins, carbohydrates, and fats in the diet. The highest energy expenditure occurs during the digestion of proteins (up to 30–40%). For fats, it ranges from 4 to 14%, and for carbohydrates, from 4 to 7%. Even a cup of tea can raise the basal metabolic rate by 8%. With a balanced intake of individual dietary components, an overall increase in basal metabolic rate of 10–15% is typically observed.

During various activities, particularly muscular work, human energy expenditure increases significantly. For instance, while reading a book raises the basal metabolic rate by only 16%, physical exertion increases it manifold.

Total energy expenditure and dietary caloric norms for the population are determined according to Dietary Guidelines recommended by the World Health Organization (WHO). However, these norms vary across countries due to differing parameters taken into account, such as age, body mass, basal metabolic rate, activity factor, etc. As shown in Table 41, the average daily energy intake for college-aged men (19–24 years) is 2900 kcal ⋅ day^-1, and for women of the same age, 2200 kcal ⋅ day^-1. For individuals with different body masses and higher physical activity levels engaged in various fields, energy expenditure depending on work intensity can range from approximately 2200–2500 kcal ⋅ day^-1 for men and 1800–2200 kcal ⋅ day^-1 for women engaged in sedentary or mental work, whereas for heavy physical laborers, it reaches up to 4300 kcal ⋅ day^-1 for men and up to 3000 kcal ⋅ day^-1 for women. Consequently, their diet must cover this energy expenditure, i.e., be more calorie-dense. Nevertheless, a chronic daily caloric surplus of just 300 kcal (the caloric content of a 100 g sweet bun) leads to the accumulation of 15–30 g of reserve fat per day, amounting to approximately 5–10 kg per year.

Energy expenditure in athletes of various specializations depends on the intensity of physical exertion and the specific sport, ranging from 2000 kcal ⋅ day^-1 for chess players and gymnasts to 7000 kcal ⋅ day^-1 for weightlifters and endurance athletes (such as cyclists).

An analysis of daily energy consumption among athletes in various sports has revealed a wide range of differences between disciplines (Table 42) and even within the same sports group (for further details, see specialized literature on sports Nutrition).

TABLE 41. Average Daily Energy Requirements

Athletes in team sports also exhibit high energy consumption, as energy expenditure in male basketball players can reach approximately 5500 kcal ⋅ day^-1. The highest energy expenditure is observed in cyclical sports requiring high overall endurance: for instance, in male road cyclists, it can reach 5900 kcal ⋅ day^-1, sometimes approaching 7000 kcal ⋅ day^-1, while in female cyclists it ranges from 2000 to 3200 kcal ⋅ day^-1; for male triathletes, it is 5230 kcal ⋅ day^-1, and for female triathletes, 4150 kcal ⋅ day^-1.

As the presented data indicate, energy expenditure in athletes is comparable to that of individuals engaged in heavy physical labor. However, when performing maximal power output work, an extremely large amount of energy is expended per unit of time. Such work is performed under anaerobic conditions (with an oxygen debt). During moderate-intensity work, the total energy expenditure of an athlete, such as a marathon runner, is 1.5–2 times higher than that of industrial workers.

Energy expenditure in athletes depends on their skill level. As athletic proficiency increases, energy expenditure during standard physical tasks decreases. Emotional state also influences energy expenditure; for instance, in the pre-start state or during competitions, energy outlays during identical work increase by 26–29% compared to regular training sessions.

TABLE 42 Average Daily Energy Consumption in Athletes of Various Specializations

The daily energy expenditure of athletes across various sports is compensated by a specific ratio of energy intake derived from carbohydrates, fats, and proteins.