— Muscular energy —

The entire muscular system accounts for nearly one-third of body weight. A muscle is a machine that converts chemical energy into mechanical energy, which serves as the driving force behind movement. It is the final link in a chain of functions that includes the heart, the nervous system, thermoregulation, energy supply, oxygenation, and waste removal. The reaction that produces muscular energy can be summarized as follows:

Nutrients + oxygen = mechanical energy + heat + waste

Nutrients are the fuels carbohydrates, proteins, and fats—produced by the digestion of food.

Oxygen enables the oxidation of nutrients and the production of energy (aerobic energy metabolism). Certain brief, intense physical activities can occur in the absence of oxygen (anaerobic energy metabolism).

The mechanical energy produced by muscle contraction is the driving force behind movement.

Like internal combustion engines, the human body is not very efficient. Only 25% of muscular energy is converted into mechanical energy, while the rest is converted into heat. This heat is carried to the skin by the blood, and it is the evaporation of sweat that helps eliminate excess calories. The fluid loss caused by sweating must be replenished by drinking.

Waste products are the end products of energy-producing reactions. In anaerobic reactions, this is lactic acid. The buildup of lactic acid causes cramps. It is also carbon dioxide, the typical waste product of aerobic reactions.

For the mountaineer, who generally engages in sustained moderate-intensity exertion, the aerobic pathway of energy production is the most important; this is the energy pathway of endurance. In the presence of oxygen, all nutrients are utilized until they are completely broken down.

Carbohydrates + Fats and Proteins + Oxygen = Energy + CO2 + H2O + Heat.

However, the activation of the aerobic pathway is delayed by the inertia of the gas exchange system. It is triggered at the start of exercise but does not become effective until a few minutes later.

At the start of exercise, energy is produced through anaerobic pathways. There are two sources of energy production in the absence of oxygen. The first results from the breakdown of phosphagen (or creatine phosphate), and the second from the breakdown of glycogen, which produces lactic acid. Glycogen is the name given to the reserve carbohydrates stored in the muscles and liver.

At the start of exercise, energy is produced through anaerobic pathways. There are two sources of energy production in the absence of oxygen. The first results from the breakdown of phosphagen (or creatine phosphate), and the second from the breakdown of glycogen, which produces lactic acid. Glycogen is the name given to the reserve carbohydrates stored in the muscles and liver.

ATP = ADP (adenosine phosphate) + phosphoric acid + energy

However, any breakdown of ATP requires repair in order to sustain the next muscle contraction. This repair process relies on glucose, which is why carbohydrates are so important for muscle energy production.

— Muscle constitution —

Muscle tissue is made up of fibers arranged in bundles.

There are two types of fibers:

slow-twitch fibers, which are suited for sustained moderate-intensity exercise, and fast-twitch fibers, which are capable of sustaining brief bursts of intense effort. Each muscle contains both types of fibers in proportions that depend on the specific activity and the level of training.

Slow-twitch fibers are highly vascularized to allow for a greater supply of oxygen and nutrients.

They contain numerous enzymes essential to the aerobic energy process. Muscles dominated by this type of fiber are suited to long, steady exertion at a level of intensity consistently below maximum capacity—this is endurance. Hiking, cross-country skiing, and moderate-difficulty mixed-terrain climbing all rely on this type of muscle.

They contain numerous enzymes that are essential for aerobic energy production. Muscles composed mainly of this type of fibre are suited to prolonged, steady exertion at an intensity level consistently below maximum capacity: this is known as endurance. Hiking, cross-country skiing and rock climbing on varied terrain of moderate difficulty all make use of this type of muscle.

— Nutrition —

When walking in the mountains, you lose around 350 kcal/hour, to which you must add 100 kcal/hour to combat the cold. For a 7-hour run, the calorie loss is therefore 7 x 450 kcal/hour, i.e. 3150 kcal. To this must be added the loss due to the remaining daily activity, i.e. some 1500 kcal.

Because of the diversity of factors involved, it is difficult to establish the precise calorific requirements of thermoregulation.
According to studies by Johnson and Kark, the caloric requirement caused by thermoregulation should be increased or decreased by 5% when the temperature varies by + or – 10 degrees in relation to an average considered to be normal.

The 4650 kcal lost will be made up in the evening or the next day by eating more and richer food. However, it is difficult to exceed a daily intake of 4,000 kcal, so there will be a calorie deficit after 5 to 6 hours of exercise, which will be made up by fat loss.

While it is generally accepted that exercise nutrition should be rich in carbohydrates, the importance of these varies from one specialist to another. In my opinion, the proportion of carbohydrates, lipids and proteins is not the same depending on whether you are doing a one- or two-day race or a race lasting several days at altitude. As a rough guide, we could give the following proportions:

In addition, it is important to respect the following ratios:

Calories from refined sugars / Total calories < or = 1/10

Animal proteins / Plant proteins > or = 1

Animal fat / Plant fat < or = 3/5

Many books dealing with exercise nutrition offer menus and publish calorie equivalence tables. Reproducing this information would go beyond the scope of this site. All we need to do is give you the following advice.

The day before a race, preferably eat slow carbohydrates in the form of pasta (not overcooked), rice or potatoes.

On the morning of the race, eat some flour (oatmeal, Bircher muesli, wholemeal bread, etc.), cheese and oilseeds (walnuts, almonds, etc.), and above all drink enough.

During the race, eat fast carbohydrates (especially fructose) in the form of dried fruit, fruit pastes, dates, agglomerated tablets, etc., and… drink regularly! When you return from the race, replenish your reserves with fresh meat and vegetables.

But above all, don’t base your menu solely on dietary recommendations, eating according to your own tastes and desires is just as important.

— Food rations —

The composition of a food ration can be determined on the basis of estimated calorie requirements.

Outside of racing, a mountaineer should consume 3500 kcal/day.

The table below gives an indication of the quantity (in grams) of nutrients to be consumed.

— Drink —

During exercise, we recommend drinking 100 to 120 ml of fluid every 20 minutes.

A mixture of water (1 litre) + squeezed lemons (2) + honey (4 teaspoons) + salt (200 to 400 mg) is recommended.