During running, athletes burn calorie, and lose water and salts in amounts depending on various factors such as the technique, training level, environmental conditions, and physiological characteristics of each runner. The knowledge of these factors allows to plan an adequate diet both during workout and recovery, with the aim of optimizing performance.
Below we will analyze the energy expenditure of runners engaged in workouts on various distances, the amounts of carbohydrates, lipids, and proteins oxidized to meet the energy requirements, and which minerals are lost in sweat.
Contents
Energy expenditure during running
During running energy expenditure is equal to 0.85-1.05 kcal per kilogram per kilometer.
This range is due to the fact that athletes with a good technique spend less than those with a poor technique.
A 70 kilogram (154 pound) athlete has an energy expenditure per kilometer between:
70 x 0.85 x 1 = 59.5 kcal
and
70 x 1.05 x 1 = 73.5 kcal
The table shows the calculations to determine the energy expenditure of the athlete to run 10, 20, 30, and 40 kilometers.
| Distance | Energy expenditure |
| 10 km | 0.85 x 70 x 10 = 595 kcal 1.05 x 70 x 10 = 735 kcal |
| 20 km | 0.85 x 70 x 20 = 1190 kcal 1.05 x 70 x 20 = 1470 kcal |
| 30 km | 0.85 x 70 x 30 = 1785 kcal 1.05 x 70 x 30 = 2205 kcal |
| 40 km | 0.85 x 70 x 40 = 2380 kcal 1.05 x 70 x 40 = 2940 kcal |
Note: who has started running for a short time ago has an energy expenditure even higher than 1.05 kcal per kilogram per kilometer.
During running, the energy for muscle work derives from the oxidation of carbohydrates, lipids, and proteins. Carbohydrates and lipids are the main energy source, and their oxidation rate depends on the intensity of exercise: as it increases, the percentage of lipid oxidation decreases whereas that of carbohydrates increases, as summarized below.
| Intensity | Fuel |
| 30 percent VO2max | Mainly fats |
| 40-60 percent VO2max | Fats and carbohydrates |
| 75 percent VO2max | Mainly carbohydrates |
| 80 percent VO2max | Almost exclusively carbohydrates |
Note: The failure to use the suitable fuel can promote fatigue and lead to overtraining.
Then, when running above the anaerobic threshold, the oxidation of carbohydrates can provide the entire energy requirement. At marathon pace, carbohydrates provide 60-70 percent of the energy requirement, whereas at lower pace they provide less than 50 percent of energy requirement.
Below, the amounts of carbohydrates, lipids, and proteins oxidized during workout are analyzed. During workout ,the energy expenditure is covered for about 60 percent by carbohydrates, for about 40 percent by lipids, whereas the residual percentage, between 3 and 5 percent, by proteins.
Carbohydrate oxidation during workout
For a 70 kilogram runner the amount of carbohydrates oxidized per kilometer is between:
(0.6 x 59.5) /4 = 8.9 g/km
and
(0.6 x 73.5) /4 = 11 g/km
Note: carbohydrates provide, on average, 4 kcal per gram.
The table shows the calculations to determine the amount of carbohydrates oxidized when the athlete runs 10, 20, 30, and 40 kilometers.
| Distance | Carbohydrate expenditure |
| 10 km | [(0.85 x 70 x 10) x 0.6 ] / 4 = 89 g [(1.05 x 70 x 10) x 0.6 ] / 4 = 110 g |
| 20 km | [(0.85 x 70 x 20) x 0.6] / 4 = 179 g [(1.05 x 70 x 20) x 0.6] / 4 = 221 g |
| 30 km | [(0.85 x 70 x 30) x 0.6] / 4 = 268 g [(1.05 x 70 x 30) x 0.6] / 4 = 331 g |
| 40 km | [(0.85 x 70 x 40) x 0.6] / 4 = 357 g [(1.05 x 70 x 40) x 0.6] / 4 = 441 g |
Lipid oxidation during workout
By calculations similar to those for carbohydrates, we determine the amount of lipids oxidized per kilometer, which is between:
(0.4 x 59.5) / 9 = 2.6 g/km
and
(0.4 x 73.5) / 9 = 3.3 g/km
Note: lipids provide, on average, 9 kcal per gram.
The table shows the calculations to determine the amount of lipids oxidized when the athlete runs 10, 20, 30, and 40 kilometers.
| Distance | Lipid expenditure |
| 10 km | [(0.85 x 70 x 10) x 0.4] / 9 = 26 g [(1.05 x 70 x 10) x 0.4] / 9 = 33 g |
| 20 km | [(0.85 x 70 x 20) x 0.4] / 9 = 53 g [(1.05 x 70 x 20) x 0.4] / 9 = 65 g |
| 30 km | [(0.85 x 70 x 30) x 0.4] / 9 = 79 g [(1.05 x 70 x 30) x 0.4] / 9 = 98 g |
| 40 km | [(0.85 x 70 x 40) x 0.4] / 9 = 106 g [(1.05 x 70 x 40) x 0.4] / 9 = 131 g |
Protein oxidation during workout
Protein requirements of adults are equal to 0.9 grams per kilogram of body weight, and, for a 70 kilogram athlete is:
70 x 0.9 = 63 g
During workout the energy expenditure is covered for about 3-5 percent by protein oxidation.
The table shows the calculations to determine the amount of proteins oxidized when the athlete runs 10, 20, 30, and 40 kilometers, and proteins provide 3 percent of the energy requirement.
| Distance | Protein expenditure (3 percent) |
| 10 km | [(0.85 x 70 x 10) x 0.03)] / 4 = 4.5 g [(1.05 x 70 x 10) x 0.03)] / 4 = 5.5 g |
| 20 km | [(0.85 x 70 x 20) x 0.03)] / 4 = 8.9 g [(1.05 x 70 x 20) x 0.03)] / 4 = 11 g |
| 30 km | [(0.85 x 70 x 30) x 0.03)] / 4 = 13.4 g [(1.05 x 70 x 30) x 0.03)] / 4 = 16.5 g |
| 40 km | [(0.85 x 70 x 40) x 0.03)] /4 = 17.9 g [(1.05 x 70 x 40) x 0.03)] /4 = 22.1 g |
Note: proteins provide, on average, 4 kcal per gram.
For energy expenditure of 0.85 and 1.05 kcal per kilogram per kilometer, the average additional protein oxidation per kilogram to run 10, 20, 30, and 40 kilometers, rounded to the second decimal place, is:
- 10 km: [(4.5 + 5.5) / 2] / 70 = 0.07 g
- 20 km: [(4.5 + 5.5) / 2] / 70 = 0.14 g
- 30 km: [(4.5 + 5.5) / 2] / 70 = 0.21 g
- 40 km: [(4.5 + 5.5) / 2] / 70 = 0.29 g
Finally, adding the daily protein requirement of adults, the total protein requirement of a 70 kilogram runner, for the four distances, is:
- 10 km: 0.07 + 0.9 = 0.97 g
- 20 km: 0.14 + 0.9 = 1.04 g
- 30 km: 0.21 + 0.9 = 1.11 g
- 40 km: 0.29 + 0.9 = 1.19 g
By calculations similar to the previous ones, we determine the overall protein requirement when proteins provide 5 percent of the energy requirement.
- 10 km: 0.12 + 0.9 = 1.02 g
- 20 km: 0.24 + 0.9 = 1.14 g
- 30 km: 0.36 + 0.9 = 1.26 g
- 40 km: 0.48 + 0.9 = 1.38 g
Excluding athletes who run 30 kilometers or more every day, the values are slightly higher than 0.9 grams per kilogram of body weight.
In reality, the daily protein requirement is just slightly higher because a certain amount of nitrogen, hence proteins, is lost, as well as in the urine, also through sweating.
Water and minerals loss during running
Water losses depend on the amount of sweat produced, that depends on:
- air temperature and humidity;
- solar radiation.
The loss will be greater the higher these values are.
Finally, the amount of sweat produced is different from person to person.
Minerals lost in sweat are mostly:
- sodium and chlorine, about 1 gram per liter of sweat in heat acclimatized athletes;
- potassium, in an amount equal to about 15 percent of the sodium lost;
- magnesium, in an amount equal to about 1 percent of the sodium lost.
The amount of minerals lost depends on how much sweat is produced, and it increases in non-heat acclimatized athletes.
The table shows the values, in grams per liter, of the minerals lost in sweat for non-heat and heat-acclimated athletes.
| Non-heat acclimated athletes |
Heat acclimated athetes | |
| Sodium | 1.38 | 0.92 |
| Chlorine | 1.5 | 1.00 |
| Potassium | 0.20 | 0.15 |
| Magnesium | 0.01 | 0.01 |
| Total | 3.09 | 2.08 |
Therefore, during physical activity, sodium is the mineral we need most of all.
After physical activity, runner, or who sweats heavily, tends to eat saltier food. This effect, known as selective hunger, was discovered, for sodium, in studies conducted on foundry workers. Probably, the selective hunger doesn’t not exist for potassium and magnesium.
References
- 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(2):377-390. doi:10.1249/mss.0b013e31802ca597
- Shirreffs S., Sawka M.N. Fluid and electrolyte needs for training, competition and recovery. J Sport Sci 2011;29:sup1, S39-S46. doi:10.1080/02640414.2011.614269