Many athletes underestimate how much energy they need to meet their needs and achieve their goals. On the other hand, they rarely overestimate how much energy they use up during a training session.

In this post, you'll learn more about where energy comes from and what role it plays, what determines energy requirements, and how you can best determine your own individual needs.

Contents:

Your organism's engine and fuel
What determines how much energy you need?
What are your energy requirements composed of?
How to determine your energy needs
How to determine your performance turnover
When do you use the most energy?
Conclusio: your energy needs...

Your organism's engine and fuel

Your engine

Your body needs energy for any form of activity. This is created in the energy metabolism by splitting the body's own energy stores of ATP (adenosine triphosphate).

Another energy-rich phosphate — creatine phosphate (CrP) — is present in small quantities in muscle cells and ensures a basic supply.  

Under stress, however, this energy source is exhausted within a few seconds, and your body has to generate energy from other substances. It burns energy-rich substrates in the muscle cells, thereby providing the energy required for muscular exertion (catabolism)¹.

Your fuel

The most important sources of energy are phosphates (especially creatine phosphate), carbohydrates, fats, and proteins.

Proteins play a subordinate role under physiological conditions during (while enduring) muscular exertion (“operating metabolism”). They are crucial for the "building metabolism" of your body (anabolism).

All energy-rich substrates are already stored in your body in varying amounts. Fats are deposited almost everywhere and also have a high energetic value (dietary fat: 9.1 kcal/g, body fat: 7.5 - 8 kcal/g).

Your body stores carbohydrates, in their storage form glycogen, exclusively in the muscles or liver, or they circulate dissolved in the blood. Carbohydrates are low in calories at 4.1 kcal per gram.

Depending on body weight and composition, this results in different storage amounts for each of your main energy sources. The example of a slim, well-trained man (180cm, 80kg, 15% body fat) demonstrates this:

These stores will empty under stress as required, according to the need and speed of energy flow.

With the exception of phosphate reserves, you replenish your stores with food. There are three ways in which your body can metabolize these energy sources into ATP (ATP resynthesis):

• The anaerobic-alactacid energy supply from energy-rich phosphates (ATP and CrP)

• The anaerobic-lactic energy supply from carbohydrates (glucose or storage form glycogen)

• The aerobic supply of energy from carbohydrates and fats (glucose or glycogen and free fatty acids or from the storage form triglycerides)

What determines how much energy you need?

Daily energy requirements depend on various factors — it is individual for each person.

These are the most important factors:

• Age (basal metabolic rate — BMR — decreases with increasing age)
• Sex: Men > Women
• Anatomy:
• Height and weight (BMR rises)
• Percent body composition (muscle mass to fat ratio) dependent on muscle mass (the more muscle mass, the higher the BMR)
• Hormones (may decrease or increase BMR)
• Stress (may increase BMR)
• Fever (may increase BMR)
• Medications (may increase BMR)
• Climate: cold > warm

The average basal metabolic rate is around 1 kcal (4.2 kJ) per kilogram of body weight per hour.

Example: A physically fit 24-year-old man who is 1.85 meters tall has a higher basal metabolic rate than a moderately fit 33-year-old woman who is 1.60 meters tall.

What are your energy requirements composed of?

The following formula is crucial for your daily energy requirements:

Basal Metabolic Rate + Power Metabolic Rate + Digestive Losses + Food-Induced Thermogenesis = Total Energy Demand

Food-induced thermogenesis concerns the energy expenditure necessary to metabolize the nutrients ingested.

In contrast to basal metabolism, performance turnover and food-induced thermogenesis, the body does not have to expend any energy for digestive losses, but instead has to compensate for energy.

Digestive losses affect about 10% of the energy contained in food: food in the body cannot be fully broken down. You excrete some of the nutrients via stool, urine, or skin.

The basal metabolic rate or resting metabolic rate describes the amount of energy that your organism needs in a state of complete rest and sober for 12 hours at a temperate temperature (clothed 20 degrees celsius, undressed 30 degrees celsius) for the sum of all metabolic activities.

The basal metabolic rate represents the largest part of the energy expenditure during normal physical exertion. As a human being you have to maintain a constant body temperature of 36-37°C. The body's own generation of heat consumes about 60% of the basal metabolic rate.

The various organ systems are involved to varying degrees in basic energy expenditure²:

The liver and skeletal muscles account for the largest share of the basal metabolic rate in the human body, each with around 26%, followed by the brain with 18%, the heart with 9%, and the kidneys with 7%. The other organs account for the remaining 14%.

The performance turnover refers to all movements or demands on your body that go beyond the basal turnover. These stresses lead to increased energy consumption:

• Muscular activity (e.g. exercise, sports)
• Energy needs for growth (in children and adolescents)
• Heat regulation (at different temperatures)
• Digestive activity
  
• Intellectual activity (minor influence)

The mass of the muscles used, as well as the intensity and duration of their exertion, are decisive for the level of power conversion.

How to determine your energy needs

You can determine your basal metabolic rate via a breath gas analysis (indirect calorimetry).

There are also now diagnostic methods that are not only used in clinical fields and competitive sports, but are affordable for ambitious amateur athletes. These will give you the most accurate results.

Another option are basal metabolic formulas that allow a rough estimate, such as the the frequently used formula by Harris and Benedict (1919):

• Men: BMR (kcal/d = 66,473 + 13,752 * body weight [kg] + 5,003 * height [cm] - 6,755 * age [years]
• Women: BMR (kcal/d) = 655,096 + 9,563 * body weight [kg] + 1,850 * height [cm] - 4,676 * age [years]

The WHO (World Health Organization) also developed gender-specific formulas together with the FAO (Food and Agriculture Organization of the United Nations). They include age as well as gender.

Basal metabolic rate according to WHO (women)

Basal metabolic rate according to WHO (men)

How to determine your performance turnover

Performance turnover usually fluctuates and depends on the intensity of the stress during your professional activities.

In addition to work turnover, individual leisure time turnover also plays a role. The performance turnover therefore refers to the entire extent of physical activity, "PAL" for short (physical activity level)³.

As an operand, the PAL describes the additional energy requirement as a multiple of the basal metabolic rate.

*An additional 0.3 PAL units per day can be added for exercise or strenuous leisure activities (30-60 minutes, 4-5 times per week).

Rough guidelines for your energy intake

The following example provides you with an overview of the average level of energy intake per day, taking into account a PAL of 1.6.4

The values apply to people with a light physical load during their workday.

 The following supplements are required for other professional groups:

• Medium-load labor: ca. 600 kcal
• Heavy work: ca. 1200 kcal
• Hard physical labor: ca. 1600 kcal

The German Society for Nutrition (DGE) provides the "Recommendations for nutrient intake" at regular intervals (according to current knowledge) with the publication of the "Reference values for nutrient intake."

When do you use the most energy?

Who would have thought? During sports, energy turnover usually reaches higher values than with "normal" work.

Here are a few examples (note: average values)⁵:

• Walking 9km/h = 10 kcal/min
• Running 15km/h = 11,4 kcal/min
• Cycling 43 km/h = 15,7 kcal/min
• Swimming 20 m / min (Brust) = 4,5 kcal/min
• Swimming 50m/min (Brust) = 11,3 kcal/min
• Handball: 19,3 kcal/min
• Soccer: 13,1 kcal/min
• Ice hockey: 22,4 kcal/min

Conclusion: your energy needs...

...are as individual as you are and can be influenced by many different factors. In particular, an increase in your muscle mass leads to a higher basal metabolic rate.

In order to determine your personal energy requirements as precisely as possible, we recommend a metabolic analysis, for example using the method of indirect calorimetry (a special form of spiroergometry, carried out, for example, on a running or bicycle ergometer).

This will not only give you information about your basal metabolic rate, but will also tell you what intensity or heart rate you should reach during training in order to optimize your energy supply.

The basic formulas are a good rough indicator, but do not include many aspects, such as your physical constitution.

¹ Vgl. De Marées, H. (2003): Sportphysiologie, 9. Aufl., Köln: Sport und Buch Strauß
² Vgl. Robert F. Schmidt, Florian Lang, Manfred Heckmann: Physiologie des Menschen. mit Pathophysiologie. 31. Auflage. Springer Medizin Verlag, Heidelberg 2010, S. 838.
³ Vgl. D-A-CH Referenzwerte für die Nährstoffzufuhr, 2. Auflage, 2. updated edition 2016
⁴ Ebd.
⁵ J. Weineck, A. Weineck: Leistungskurs Sport. 3. Auflage. Band 1. Forchheim 2004.

Article written by Vanessa Barthels (txt-box.de , instagram.com)