Calories burned, water and minerals lost during running

Fig. 1 – Marathon

During running, energy expenditure is equal to:

0.85-1.05 kcal/kg of body weight/km

The range is due to the fact that athletes with a “cheaper” athletic technique expend less than those with a less refined technique.
Moreover, we must underline that  who have recently started running have expenditures even higher than 1.05 kcal/kg of body weight/km.

How many calories does a 70 kg (154 pound) athlete, with a good technique, expend if he runs for 10, 20, 30 or 40 km?
The expenditure/km is between:

70×0.85=59.5 Kcal and 70×1.05=73.5 Kcal/km.

For increasing mileage, with the following calculations,

runningwe obtain:

  • 10 km: 595-735 kcal
  • 20 km: 1190-1470 kcal
  • 30 km: 1785-2205 kcal
  • 40 km: 2380-2940 kcal

What does he consume during running?
He consumes:

Carbohydrate consumption during running

Carbohydrate consumption is affected, like for lipids, by the exercise intensity:

    • for running higher than anaerobic threshold, therefore the athlete is going very fast, only those are consumed;
    • in the pace typical of marathon, they supply 60-70% of the energy;
    • for pace lower than that of marathon, they supply less 50% of energy.
Fig. 2 – Exercise Intensity and Fuel Sources

During workout, energy expenditure is sustained, on average, for 60% by carbohydrates and the remaining 40% by lipids.

Carbohydrate consumption during workout

If we consider a 70 Kg (154 pound) athlete, carbohydrate consumption (in grams) to supply the aforementioned 60% for 10 km (energy expenditure between 595 and 735 kcal) is equal to:

(0.6×595)/4=about 90 g and (0.6×735)/4=about 110 g

where: carbohydrates=roughly 4 calories per gram.
For the other distances, with the following calculations,

we obtain:

  • 20 km: 180-220 g
  • 30 km: 270-330 g
  • 40 km: 360-440 g

Lipid consumption during workout

With calculations as those made for carbohydrates,

we obtain a lipid consumption (40% of energy) for the just seen distances equal to:

  • 10 km: 26-32 g
  • 20 km: 53-65 g
  • 30 km: 80-100 g
  • 40 km: 105-130 g

Arcelli’s formula

A formula, called “Arcelli’s formula”, exists by which we can estimate the grams of lipids consumed during running/walking:

grams of consumed lipids=(km x kg of body weight)/20 (30 if we walks).

Lipid intake, that are present in almost all foods, is not a problem, but it is very important because source of essential fatty acids, omega-6 and, above all, omega-3.

Daily protein requirements and running

Protein requirements of a sedentary man (adult) are equal to 0.8 g/kg of body weight/day (OMS source).
So, the basal requirements of the 70 kg (154 pound) athlete are :

0x0.8=56 g/day

About 3-5% of the energy expended to sustain muscular work comes from amino acids (coming from proteins) oxidation.
With calculations as those made for carbohydrates and lipids,

for the just seen distances, we obtain:

  • 10 km: 61-64 g (0.87-0.92 g/kg of body weight/day)
  • 20 km: 66-73 g (0.94-1.04 g/ kg of body weight/day)
  • 30 km: 71-81 g (1.01-1.16 g/ kg of body weight/day)
  • 40 km: 76-89 g (1.09-1.28 g/ kg of body weight/day)

Leaving out athletes who train daily for 30 km or more, we obtain values slightly higher than 0.8/kg of body weight/day of the general sedentary population.
Actually, the amount is a bit to increase because some nitrogen (proteins) is lost with sweating as well as urine.
Howeve, we are always at lower values than 1.5 g/kg of body weight/day.

Fluid and mineral loss during running

Water losses depend on the amount of sweat that athlete produces that in turn depend on:

  • air temperature and humidity;
  • solar radiation.

The loss will be greater the higher these values are.
Finally, sweat is produced in different amount in any person.

By sweat, mineral lost are mostly:

  • sodium (Na+) and chlorine (Cl), about 1 g/L of sweat in athlete accustomed to train in environmental conditions that cause a great sweating;
  • potassium (K+) about 15% of sodium;
  • magnesium (Mg2+) still less, about 1% of sodium.
Fig. 3 – Mineral Salts and Sweat

The amount of mineral salt lost depends on how much sweat we produce, and it increases if we consider not accustomed athletes.

Physical activity and sodium

During physical activity, the mineral we need most of all is sodium.
After physical activity, runner or who sweats very much (studies conducted initially on foundry workers) tends to eat saltier, both as food and as salt on food. We talk of “selective hunger”.
Probably, the “selective hunger” doesn’t not exist for potassium and magnesium (it seems that is not true for all subjects, usually 2 of 3).


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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

Shils M.E., Olson J.A., Shike M., Ross A.C.: “Modern nutrition in health and disease” 9th ed. 1999

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

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