Evaluation of chemical composition and energy value of of the diets of highly skilled athletes

Abstract


159 highly skilled athletes were surveyed in the pre-competition period of sports training. A comparative assessment of the energy value and chemical composition of athletes diets on the basis of the questionnaire method of 24-hour (daily) reproduction of nutrition showed significant variability and dependence on the type of sports specialization of activities and gender of athletes. In particular, statistically significant (p <0.05) increase in the energy consumption value of rations in biathlonists was shown in comparison with athletes specializing in bullet shooting of various specializations of bobsleigh (overclockers and pilots) both in the male group (33.4%, 14, 8%, 31.5%), respectively, and female (33.9%, 13.8%, 41.7%), respectively. In the bobsledder of both sex groups specializing in overclocking, the energy values of rations were also statistically higher than those of athletes from the group of bullet shooting and bobsleigh pilots: by 21.7% and 19.6%, respectively, in the male group and 23.2% and 32.3%, respectively, in the female. Depending on the type of athletic activity and gender of athletes, the consumption of the main macro-intravenous animals varied significantly. In particular, the amount of protein ranged from 119.2 to 200.2 g/day in men and from 79.5 to 170.1 g/day in women; fat - 119.1-164.2 g / day for men and 84.6-148.8 g/day for women; carbohydrates - 385.1-594.6 g/day, in men and 285.5-475.6 in women.


INTRODUCTION The training and competitive activity of athletes is held in conditions of excessive physical, neuro-emotional tension and is associated with extreme energy consumption. Intense physical exercises, in the absence of a full recovery, lead to disadaptation of the functional systems and the development of fatigue [1-3]. There are different ways and methods to restore physical activity of athletes. However, one of the most important factors for achieving high sports results, maintaining health, reducing the risk of morbidity and the occurrence of injuries, is adequate food intake [4-9]. The needs of athletes in food substances are significantly different from those of people who do not engage in sports. This is due to the intense physical and emotional stresses experienced by athletes during the process of training [5, 10, 11]. For example, during excessive physical exertion, the daily energy expenditure of athletes reaches 5000-6000 kcal, in some cases 10,000 kcal per day [12]. In this regard, the nutrition of athletes is characterized by an increased intake of nutrients. Depending on the intensity of physical activity and the stage of sports training, the intake of proteins, fats and carbohydrates in athletes can vary between 1.6-2.9; 1.5-2.4; 7-10 g/kg body weight per day, respectively [13, 14]. Along with macronutrients, the attention is also demanded by the issues of ensuring the diet of athletes with vitamins and microelements [15-18]. When compiling a diet, it is extremely important to take into account many individual physiological characteristics of athletes, such as age, sex, body weight, taste preference. In addition, it is necessary to take into account the main factors related to sports activity, such as sports specialization (rind of sport activity), intensity of training, period of sports training, etc. The athlete's diet should fully satisfy the energy and plastic needs of the body. The problem of rational and balanced nutrition - is one of the main factors in the overall system of training of highly qualified athletes. Balanced nutrition, which takes into account the characteristics of sports activities, is one of the most crucial factors for achieving optimal sport results. In the field of sports medicine the great attention especially for highly skilled athletes is paid to the issues of qualitative and quantitative balance of dietary nutrients [19, 20]. It is established that a prolonged violation of the athlete’s nutrition balance can lead to the development of disturbances in the functioning of a number of basic physiological systems of the organism, which leads to the reduction os physical performance [5, 10, 11, 21-23]. In this regard, there is a need for more in-depth study and individualization of components of energy consumption and nutritional needs of athletes of different specializations, depending on the stage of training and competitive activities. The goal of this study was a comparative assessment of the chemical composition (CC) and energy value (EV) diets for athletes of various sports specializations that require different levels of energy consumption. MATERIALS AND METODS Examination of athletes was conducted in the pre-competition period of their sports training. All the examinees gave written informed consent to participate in the study. The age of the men tested was 21.7 ± 0.8 years (a maximum of 29, a minimum of 18); women - 23.1 ± 1.5 years (a maximum of 33, a minimum of 19). 159 highly skilled athletes of both gender groups of different sports specialization and qualifications were examined. Depending on the sports specialization, the athletes were divided into the following groups: ♦ Bobsleighs of various specializations, including 35 men (overclocking - 28 and pilots - 7) and 24 women (18 and 6, respectively). ♦ Biathlonists (n = 30, 20 men and 10 women). ♦ Bullet shouting athletes (n = 70, 37 men and 33 women) The data on the actual nutrition of the subjects was conducted using the questionnaire-method (reproduction of 24-hour food intake), which is actively used in sports practice [24]. Determination of the amount of food consumed was carried out using the “Album of food and food portions” developed by Federal Center of nutrition and Biotechnology. The calculation of the consumption of nutrients and energy was carried out using an electronic database of the chemical composition of foods and dishes [25, 26]. The results of the studies are presented as mean values and the standard error of the mean value (M ± ± m). Evaluation of the reliability of differences in mean values was carried out using Student’s t-test. The significance level was considered reliable at p < 0.05. Results and discussion The studies revealed significant differences in the energy value of diets in different groups of athletes (Tables 1 and 2). A comparative analysis of the diet EV of the athletes groups revealed higher values of this parameter for athletes engaged in biathlon compared to groups of athletes specializing in shooting and bobsleigh. These rates were statistically significantly increased (p < 0.05) both in the male group (by 33.4%, 14.8% and 31.5%, respectively), and in the female group (by 33.9%, 13.8%% and 41.7%, respectively). This was confirmation of similar to previous data , indicating high values of EV rations in cyclists sportsmen [20]. Table 1 The content of of basic nutrients and the energy value of the diet in athletes - men (M ± m) Chemical composition of the diet Athletes groups Bullet shooting Biathlon Bobsled (overclocking) Bobsled (pilot) Norm [31] Energy value, kcal (of them BAA) 3 455 ± 261 (125 ± 50) 5 187 ± 320#*· (507,5 ± 150) 4 415 ± 310*· (373 ± 70) 3 550 ± 275 (250 ± 70) 4 375 Proteins, g (of them BAA) 119,2 ± 6,5 200,2 ± 9,8#*· (30,1) 153,6 ± 10,7*· (14,4) 110,3 ± 8,7 (14,4) 117 Fats, g (of them BAA) 126,1 ± 7,7 164,2 ± 6,2*· (10,5) 148,3 ± 9,3*· 119,1 ± 17,2 154 Carbohydrates, g (of them BAA) 392,8 ± 14,9 594,6 ± 21,8*·# (82,5) 503,7 ± 34,8 (75)*· 385,1 ± 52,2 (75) 586 Complex carbohydrates, g 209,1 ± 13,4 257,9 ± 20,6*·# 214,6 ± 27,2 197,2 ± 39,6 Notes: * - compared to the bullet shooting, р < 0,05; # - comparison with the bobsleigh group (overclocking), р < 0,05; · - compared to the bobsleigh group (pilot), р < 0,05; ° - compared to the biathlon group; D - compared to the groups of shooting and biathlon , р < 0,05. Table 2 The content of basic nutrients and the energy value of the diet of athletes - women (M ± m) Chemical composition of the diet Athletes groups Bullet shooting Biathlon Bobsled (overclocking) Bobsled (pilots) Norm [31] Energy value, kcal (of them BAA) 2 914 ± 230 (125 ± 50) 4 409 ± 456#*· (507,5 ± 150) 3 798 ± 405*· (373 ± 70) 2 570 ± 86,3 (270 ± 50) 3 036 Proteins, g (of them BAA) 107,7 ± 4,9 170,1 ± 11,4#*· (30,1) 99,6 ± 9,6· (7,2) 79,5 ± 3,5· (7,2) 87 Fats, g (of them BAA) 115,01 ± 6,8· 148,8 ± 11,5*·# (10,5) 121,4 ± 17,9· 84,6 ± 12,5 102 Carbohydrates, g (of them BAA) 296,1 ± 13 475,6 ± 29,2*·# (82,5) 405,6 ± 30,6*· (50) 285,5 ± 27,5 (50) 462 Complex carbohydrates, g 153,8 ± 10,4 194,9 ± 26,2 169,9 ± 38,1 154,3 ± 22,2 Notes: * - compared to the bullet shooting, р < 0,05; # - comparison with the bobsleigh group (overclocking), р < 0,05; · - compared to the bobsleigh group (pilot), р < 0,05; ° - compared to the biathlon group; D - compared to the groups of shooting and biathlon , р < 0,05. In the bobsledder's (overclocking) of both gender groups, the EVof the diet was also higher (p < 0.05) in comparison to data of the bullet athletes and the bobsleigh pilots (by 21.7%, 19.6%, respectively, in the male group and 23.2%, 32.3%, respectively, in the female). Calculation of the nutritional value of diets of athletes revealed significant differences in consumption of basic nutrients (Tables 1 and 2). It was found that biathletes are consuming the highest number of basic macronutrients. Thus, the protein intake in the group of these male athletes was significantly higher (p < 0.05) compared to the data of the bullet shooting, bobsled overclocking and pilots athletes by 40.4%, 23.2%, 44.9%, respectively. Analysis of fat consumption also revealed a significant (p < 0.05) increase in this parameter in male biathlonists versus bullets and bobsleigh pilots by 23.2% and 27.5%, respectively. Consumption of fats in the group of male biathlonists had only a tendency, but was statistically unreliable to increase (by 9.7%), relative to the data of the bobsledder overclocking group. In the consumption of carbohydrates, between the groups of athletes, there were also differences. In particular, in biathlon group the consumption of carbohydrates were significantly higher (p < 0.05) by 33.9%, 15.2%, and 35.2%, respectively, compared to similar data in the groups of bullet shouting and bobsleigh. The actual intake of complex carbohydrates in the group of biathlon (men) was 257.9 gr. and turned out to be higher (p < 0.05) than in the other groups of athletes - bullets and bobsleders (overclocking and pilots) by 18.9%, 16.7%, 23.5%, respectively. Despite the fact that in the male biathletes, the consumption of the total consumption of carbohydrates was significantly higher in comparison to other studied athletes, complex carbohydrates accounted for 43.3%, whereas in the compared groups this was 53.2% for bullet shooting athletes, 42.6% - bobsledder overclocking and 51.2% for bobsleigh-pilots. It should be noted that in total diet consumption of proteins, fats and carbohydrates macronutrients partially was consuming with the specialized sports nutrition products and dietary supplements (Table 1). So the share of proteins in these sports products was 30.1 g (15% of the total consumed macronutrients), fats - 10.5 g (6.4%) and carbohydrates - 82.5 g (13.8%) of the total number of macronutrients consumed. It should also be noted that in the group of male biathlonists, the consumption of macronutrients was higher than the norms of physiological needs for energy and nutrients for the RF population [27], which is fully justified by the energy expenditure of athletes. The highest rates were demonstrated in protein intake, the average values of which were higher by 41.5% compared to the norm for non-athletes. The ratio of consumed proteins, fats, carbohydrates in the group of biathlon men was 1 : 0.8 : 2.9, respectively, which is important to note does not meet the requirements of a balanced diet for athletes of this category [20]. Thus, proteins, fats and carbohydrates accounted for 20.8%, 17.1% and 62%, respectively. For the women’s biathlon group, the protein intake was also significantly higher (p < 0.05) by 36.6%, 41.4%, 53.2%, respectively, compared to the data of the group of bullet shooting, bobsledders. The analysis of fat consumption in this group showed a significant (p < 0.05) increase in athletes of bullet shooting and bobsled (overclocking and pilots) by 22.7%, 18.4%, 43.1%, respectively. The carbohydrate intake in this group was also higher (p < 0.05) than in the compared groups of athletes (by 37.7%, 14.7%, 40%, respectively). Despite the pronounced tendency to increase the actual consumption of complex carbohydrates in the biathlon group (194.9 g), which was higher by 21%, 12.8%, 20.8% of similar data of the shooting groups and both bobsleigh specializations, these values were statistically unreliable. At the same time, it was noted that as a percentage of the total amount of carbohydrates consumed, 40.9% of the complex carbohydrates accounted for, whereas in the compared groups this value was: 52% - a group of athletes of bullet shooting, 41.8% - bobsledder overclocking and 54% are bobsledder pilots. In order to enrich the diet, provide energy training and recovery, athletes activelyuse specialized products to feed athletes. The share of proteins, fats and carbohydrates at the expense of these products in the biathlonist group accounted for 17.6%, 7%, 17.3%, respectively, of the total number of consumed macronutrients. When comparing the main macronutrients consumed with the recommended values of physiological requirements for energy and nutrients, an increase in these parameters in the biathlon group was also revealed. In particular, the consumption of proteins and fats was higher than the norms recommended for the general population of people by 48.9%, and 31.4%, respectively. At the same time, the level of carbohydrate intake was slightly different from the norm. The ratio of consumed proteins, fats and carbohydrates in the women’s biathlon group was 1 : 0.87 : 2.8, respectively, which also reflects the imbalance in the diet. Thus, proteins, fats and carbohydrates accounted for 21.4%, 18.7% and 59.8%, respectively, of the caloric intake of athletes. Similar studies conducted in the bobsledder group of both gender groups. In the male group, which specializes in overclocking, compared with similar data of bullet and bobsleigh pilots, a significant increase (p < 0.05) in consumed proteins was detected by 22.4%, 28.1% and fat by 15%, 19.6% respectively. Carbohydrate intake in this group was also significantly (p < 0.05) higher by 22%, 23.5%, respectively, in comparison to groups of bullets and bobsleigh pilots. The actual consumption of complex carbohydrates in the bobsled group (overclocking) was 214.6 ± 27.2 gr. and this was insignificantly higher than the data in the group of bullet shooting and bobsleigh pilots. In a comparative analysis of the consumption of the main macronutrients by athletes with the indices of physiological requirements for energy and nutrients, an increase in the protein indices of athletes by 23.8% was revealed. As for fats and carbohydrates, these were lower than the recommended values by 3.8% and 16.3%, respectively. The ratio of consumed proteins, fats and carbohydrates in the group of male bobsledder (overclocking) was 1 : 0.96 : 3.2. Thus, protein, fat and carbohydrates accounted for 19%, 18.4% and 62.5%, respectively, of the caloric intake of athletes. In the female bobsled group (overclocking), the intake of proteins and fats was significantly (p < 0.05) higher by 20.1% and 30.3%, respectively, compared to the bobsleigh (pilot) group. Carbohydrate intake in the bobsledder group (overclocking) was also significantly (p < 0.05) higher by 26.9%, 29.6%, respectively, compared to the groups with bullet shooting and bobsleigh (pilot). The actual consumption of complex carbohydrates in this group was 169.9 ± ± 38.1 gr. and had a statistically unreliable upward trend of 9.4%, 9.1%, respectively, compared to the groups of bullet shooting and bobsleigh-pilots. Consumption of proteins and carbohydrates at the expense of specialized products for athletes was 7.2%, 12.3%, respectively. Consumption of fats due to specialized products in the bobsled group (overclocking) was not noted. It should be noted that in this group of bobsledder, the consumption of proteins and fats was higher by 14.4% and 19%, respectively, compared with the norm of physiological needs for energy and nutrients. At the same time, carbohydrate intake in this group was lower by 14%. The ratio of consumed proteins, fats and carbohydrates was: 1 : 1.21 : 4.07. Thus, proteins, fats and carbohydrates accounted for 21%, 18.7% and 59.8%, respectively, of the caloric intake of athletes specializing in bobsled. In the male bobsleigh group (pilot), the average values of protein, fat and carbohydrate intake were 110.3 ± 8.7; 119.1 ± 17.2 and 385.1 ± 52.2, respectively. At the same time, the share of proteins and carbohydrates, obtained from specialized products for athletes, accounted for 13%, 19.4%, respectively. The actual consumption of complex carbohydrates in this group was 197.2 ± 39.6 gr., which is 51.2% of the total carbohydrate intake. Comparative analysis between the norms of physiological needs in energy and nutrients with actual consumption of proteins, fats and carbohydrates in athletes also revealed a discrepancy between the last values of the recommended norms. In particular, it was found that the intake of proteins, fats and carbohydrates in the group of athletes was below the recommended rates by 6%, 29.3% and 52.1%, respectively. The ratio of consumed proteins, fats and carbohydrates in the bobsleigh pilot group was: 1 : 1.08 : 3.5. Thus, proteins, fats and carbohydrates accounted for 17.9%, 19.3% and 62.6%, respectively, of the caloric intake of athletes. Similar data were obtained in the women’s group of bobsledder-pilots athletes. It is shown that the intake of proteins of fats and carbohydrates in this group turned out to be below the recommended norms of physiological needs for energy and food substances by 9.4%, 20.5% and 61.8%, respectively. The proportion of proteins and carbohydrates, obtained by athletes due to specialized products for athletes, accounted for 9% and 17.5%, respectively. The actual intake of complex carbohydrates was 154.3 ± 22.2 gr., Which is 54% of the total carbohydrate intake. The ratio of consumed proteins, fats and carbohydrates was 1 : 1.06 : 3.6. Thus, protein, fat and carbohydrates accounted for 17.6%, 18.8% and 63.5%, respectively, of caloric intake of athletes. Analysis of the consumption of macronutrients in the group of men who specialize in bullet shooting showed that proteins, fats and carbohydrates represents by 18.6%, 19.7% and 61.5%, respectively, of the total caloric intake. Athletes of bullet shooting of both gender groups, also used specialized sport nutrition products. However, the total it was low calories due to specialized products and did not exceed 125 kcal. The actual intake of complex carbohydrates in this group of athletes was 209.1 ± 13.4 gr. (53.2% of total carbohydrate intake. The ratio of consumed proteins, fats and carbohydrates in the group of bullet shooting athletes was 1 : 1.05 : 3.31. In the women of this type of sport, the fat intake was significantly higher by 26.4%, compared to the similar data of the bobsled (p < 0.05). The ratio of consumed proteins, fats and carbohydrates was 1 : 0.87 : 2.8. Thus, proteins, fats and carbohydrates account for 20.7%, 22.1% and 57.1%, respectively, of the total caloric intake of athletes. The actual intake of complex carbohydrates was 153.8 ± 10.4 gr., which corresponds to 52.2% of the total consumption of carbohydrates. Thus, comparative studies of the nutrition of athletes indicates the presence of significant variability, depending on the sport specializations and gender of athletes. It should be emphasized that the diet of athletes of course, requires more in-depth analysis and correction, taking into account both gender differences, and the types of sports activity, and the stages athletes training. At the same time, taking into account high energy requirements, especially in cyclic type of sports, in order to fully restore energy reserves, not only a balanced diet is required, but also controlled use of specialized products for athlete nutrition [17, 28-30].

R M Radzhabadiev

Federal Research Centre of Nutrition and Biotechnology

Author for correspondence.
Email: khanferyan@ion.ru

V S Evstratova

Federal Research Centre of Nutrition and Biotechnology

Email: khanferyan@ion.ru

T N Solntseva

Federal Research Centre of Nutrition and Biotechnology

Email: khanferyan@ion.ru

A S Samoilov

State research Center named by Burnasyan of the Federal Medico-Biological Agency of Russia

Email: khanferyan@ion.ru

F Diel

Institute fur Umwelt und Gesundheit

Email: khanferyan@ion.ru

Roman Avakovich Khanferyan

Federal Research Centre of Nutrition and Biotechnology; Peoples’ Friendship University of Russia (RUDN University)

Email: khanferyan@ion.ru

Doctor of Medical Sciences, Professor, Head of the Laboratory of Immunology Federal Research Centre of Nutrition and Biotechnology

  • Kochetkova S.V., Koroleva T.P., Udovenko I.L. Factors that contribute to neuropsychic health of athletes-shooters. Uchenye zapiski universiteta imeni P.F. Lesgafta. 2010. V. 8. P. 49—54.
  • Platonov V. Overtraining in sport. Science in Olympic sports. 2015. V. 1. P. 19—34.
  • Fundin N.A., Vagin Y.E. Analysis of sports activities from the standpoint of the theory of functional systems. Sechenovskiy Vestnik. 2016. V. 3. P. 34—45.
  • Topanov A.A. Assessment of nutritional status and individual power correction of young athletes. Abstract of dissertation. 2009.
  • Thomas D.T., Erdman K.A., Burke L.M. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. J. Acad. Nutr. Diet. 2016. V. 116. P. 501—528.
  • Borisov O.O. Nutrition for athletes: foreign experience and practical advice. M.: Soviet sport. 2007. P. 132.
  • Volgarev M.N., Korovnikov K.A., Yalova I.M., Azizbekyan G.A. Peculiarities of nutrition of athletes. Theory and practice of physical culture. 1985. V. 1. P. 34—39.
  • Pokrovskiy A.A. Guidelines on nutrition for athletes. Moscow: FIS, 1975. P. 57.
  • Tutelian V.A., Nikityuk D.B., Pozdnyakov A.L. Optimizing nutrition for athletes: realities and perspectives. Problems of Nutrition. 2010. V. 3. P. 78—82.
  • Manore M.M., Thompson J.L. Energy requirements of the athlete: assessment and evidence of energy efficiency. In Burke L, Deakin V, eds. Clinical Sports Nutrition. 5th ed. eds. Sydney Australia: McGraw-Hill; 2015. P. 114—139.
  • Burke L.M. Energy needs of athletes. J. Appl. Physiol. 2001. V. 26. P. 202—219.
  • Grigorev V.I. Culture of power of the athlete. SPb.: SPBGUEF. 2011. P. 191.
  • Hawley J.A., Burke L.M. Peak Performance: Training and Nutrition Strategies for Sport. Sydney, Australia: Allen Unwin. 1998. P. 233—260.
  • Polievsky C.A. Basics of individual and collective power athletes. Physical education and sport. 2005. P. 384.
  • Baranov A.A., Korneeva I.T., Makarova S.G., Polyakov S.D., Borovik T.E., Chumbadze T.R. Nutritional support and treatment and recovery measures in children's and youth sports. M.: Pediatrist, 2015. P. 164.
  • Kodentsova V.M., Vrzhesinskaya O.A., Nikityuk D.B. Vitamins in the diet of athletes. Problems of Nutrition. 2009. V. 3. P. 60—75.
  • Troegubova N.A., Rylova N.V., Samoilov A.S. Micronutrients in the diet of athletes. Practical medicine. 2014. V. P. 46—49.
  • Vrzhesinskaya O.A., Kodentsova V.M. Vitamins in nutrition of young athletes. Pediatric Nutrition. 2010. V. 4. P. 29—36
  • Baranov A.A., Makarova S.G., Borovik T.E., Korneeva I.T., Polyakov S.D., Chumbadze T.R. Nutritional support of young sportsmen with the use of a specialized domestic product. Pediatric pharmacology. 2013. V. 6. P. 78—86.
  • Makarova S.G., Chumbadze T.R., Polyakov S.D. Features of nutrition of young athletes engaged in cyclical sports. Current Pediatrics. 2015. V. 3 (T. 14). P. 332—340.
  • Mc Ardle W.D., Katch F.I., Katch V.L. Sports and exercise nutrition. 4th edn. Wolters Kluver Health. 2013. P. 682.
  • Sally S., Anderson J., Harris S., Steven J. Care of the young athlete. American Academy of Orthopedic Surgeons. 2010. P. 612.
  • Kiens B., Helge J. W. Effect of high-fat diets on exercise performance. Proc. Nutr. Soc. 1998. V. 57. P. 73—75.
  • Capling L., Beck K.L., Gifford J.A., Slater G., Flood V.M., O’Connor H. Validity of Dietary Assessment in Athletes: A Systematic Review. Nutrients. 2017. V. 9. P. 1313.
  • Skurikhin I.M., Tutelyan V.A. Chemical composition of Russian food products. М.: DeLi. 1996. P. 183.
  • Tutelyan V.A. Chemical composition and caloric content of Russian food products. М.: DeLi. 2012. P. 283.
  • Norms of physiological needs in energy and nutrients for various groups of the population of the Russian Federation. M., 2008. P. 50.
  • Aranson M.V., Portugalov S.N. Sports nutrition: the state of the issue and actual problems. Vestnik sportivnoy nauki. 2011. V. 1. P. 33—37.
  • Latkov N.Y., Vekovtsev A.A., Petrov A.V., Poznyakovskiy V.M. Nutrition of athletes during the training period: Effectiveness of BAA application. Vestnik SUSU. A series of “Food and biotechnologies”. 2015. V. 4. P. 88—93.
  • Rylova N.V., Kavelina V.S., Biktimirova A.A. Modern tendencies in nutrition of athletes. Sports medicine: Science and practice. 2014. V. 3. P. 38—47.

Views

Abstract - 114

PDF (Mlt) - 61


Copyright (c) 2018 Radzhabadiev R.M., Evstratova V.S., Solntseva T.N., Samoilov A.S., Diel F., Khanferyan R.A.

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.