Where does the word muscle come from?

Sports Nutrition Basics

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  2. Sports nutrition
  3. Basics

The sport term

"Sports" is not very easy to define, as this term conceals various layers. The German Olympic Sports Confederation characterizes sport as follows:

"Under the term Sports various forms of exercise, play and competition, which are mostly related to physical activities of humans, are summarized. The word was derived from English in the 19th century "Sports" [Fun, pleasure, relaxation - d. Ed.], The [...] in Latin "disportare" (to disperse) goes back. "

Levels of sport

Sport can be divided into different levels. Depending on the extent to which it is operated and the underlying objective. The illustration shows a possible classification that can be traced back to Digel and Burk.

Fig .: Classification and characteristics of the sports levels (based on Digel & Burk, 2002)

Classification of sports

The variety and range of sports are huge and they are constantly evolving. To keep an overview, it can help to classify the individual sports in groups. Decisive criteria for a classification can be e.g. B. the requirements - i.e. whether strength or endurance is required - and the objective of the respective sport (see table).

sportRequirements and objectivesExamples
Endurance sports - long exposure time
- continuous stress
- Endurance
- Marathon, triathlon
- long distance running
Weight training - Maximum strength development
- increased muscle mass
- Speed ​​strength, coordination
- weightlifting
- Powerlifting
- bodybuilding
Endurance sports with
high effort
- Combination of strength, endurance
- continuous endurance
- canoe
- To go biking
- cross-country skiing
Speed ​​strength sports - Combination of strength, speed
- Maximum strength, strength endurance
- coordination
- push disciplines
- Jump disciplines
- short distance runs
- Do gymnastics
Game sports - interval-like permanent loads
- Speed, quickness
- coordination
- football, handball
- tennis
Martial arts - Speed, quickness
- Maximum strength, endurance
- agility
- interval-like permanent loads
- Wrestling, judo
- karate
- boxing
Unclassified sports- poor profile
(Coordination, motor skills)
- archery
- Sailing
- motorsport
- Horse riding

Tab .: Classification and characteristics of the sports groups (according to Weineck, 2010 & Konopka, 2006)

Musculature

Movements are only possible through the work of the muscles. Athletic (top) performance in particular would be unthinkable without appropriately trained muscles. With around 400 muscles, which make up around 40% of body weight, humans have great potential in this regard.

Structure and functionality

The muscle is a bit like an onion: under each layer there is another layer. However, the highly structured muscle is much more complex. A muscle is made of firming connective tissue, the so-called Fascia, surround. This encloses a number of adjacent ones Muscle fibers (= muscle fiber bundles).

A muscle fiber, in turn, consists of a large number of thread-like fibers Myofibrils (= muscle cells). They can also be divided into subsections, the Sarcomeres. Each sarcomere contains the contractile protein structures actin and myosin, which ultimately ensure muscle contraction (see illustration). During muscle contraction, the two muscle filaments actin and myosin slide telescopically into one another, causing the muscle to shorten (Slip theory of filaments).

Fig .: Structure of a muscle

In order for the muscle contraction to run smoothly, besides the minerals calcium and magnesium, above all else energy necessary. The energy for muscle work is mainly provided in the body by two energy-rich phosphate compounds: Creatine phosphate (KP) and Adenosine tri-phosphate (ATP). The mineral calcium is important in the contraction of the muscle, magnesium, on the other hand, promotes muscle relaxation after the contraction. Cramps are therefore often due to a magnesium deficiency (Gekle et al., 2010).

Muscle fiber types

The demands on a muscle vary depending on whether it is more speed or endurance required. The muscle meets the various demands through different fiber types. So the back muscles z. B. perform long-lasting holding work and is therefore rich in the fatigue-resistant red muscle fibers. In comparison, the eye muscles have to perform many quick, short movements, which is their predominant part white muscle fibers enable.

The predominant type of muscle fiber that is present determines the type of energy production in the muscle: Red muscle fibers are especially for long-lasting endurance exercise suitable (aerobic, with oxygen). They mainly use carbohydrates and fats as fuel. White muscle fibers however, that especially for short, vigorous movements responsible have a higher phosphate store. They get their energy mainly from KP, ATP and the anaerobic way of burning carbohydrates.

Muscle fibers can be divided into three types:

descriptionproperties
Red muscle fibers
(Type I; ST fibers)
- small diameter
- rich in myoglobin
- fatigue resistant
- slowly twitching
Intermediate muscle fibers
(Type II a / c, FTO fibers)
- relatively fatigue-resistant
- twitching quickly
White muscle fibers
(Type II b, FT fibers)
- larger diameter
- less myoglobin
- easily fatigued
- twitching quickly

Tab .: Classification and characteristics of the muscle fiber types (Gekle et al., 2010)

The skeletal muscles usually consist of a mixture of different muscle fibers. However, the relationship can differ between the muscles and is also different from person to person. The type of physical exercise also influences muscle growth. For example, endurance long-distance runners sensibly have a high number of slow-twitch muscle fibers, whereas 100 m sprinters, in line with the short-term maximum performance they require, have more fast-twitch muscle fibers.

Energy generation in the muscle

By burning the main nutrients (carbohydrates, fats, proteins) the body gains energy in the form of Adenosine tri-phosphate. Not all energy is needed immediately, so some of it is temporarily stored as creatine phosphate, glycogen or fat in order to recover ATP from it later - if necessary.

The following energy stores are available to the body:

Energy storageBody memory [kcal]Body memory [kJ]ATP formation rate [mmol / min]
ATP
Creatine phosphate
Glycogen
Fat (triglycerides)

Tab .: Energy storage of a 75 kg person (Weineck, 2010)

When and how the energy sources ATP, KP, glycogen and fat are used depends on the type and duration of the sporting activity (see figure).

Fig .: Type of energy supply depending on the load duration I (modified from Leitzmann, 2009)

The energy is obtained from the energy carriers in three different ways. Which route is used determines, among other things, the duration and intensity of exercise as well as the oxygen supply (see table).

Type of provisiondescription
Anaerobic alactacid - via ATP and KP
- without oxygen
- no formation of lactic acid (lactate)
- short, explosive loads (max. 2 - 20 s)
Anaerobic lactic acid - from the breakdown of glucose / glycogen
- if there is a lack of oxygen
- with the formation of lactate
- for intensive loads up to 2 min
Aerobic (alactazid) - from the complete burning of the macronutrients
(Carbohydrates, fats, possibly also proteins)
- while consuming oxygen
- no formation of lactic acid (lactate)
- long-term, moderate loads (> 30 min)

Tab .: Types of energy supply (Konopka, 2006)

The table clearly shows that the rapidly available energy reserves are only available to a limited extent. This is how the energy is provided ATP and KP directly, but the available amount of these energy suppliers is only enough for few seconds out. With prolonged muscle work, the muscle is supplied with energy through the breakdown of glucose or fatty acids. The largest and almost inexhaustible storage area is around 50,000 kcal in adipose tissue. However, because a lot of oxygen is required to release energy from fat, this nutrient is only used to a greater extent with moderate and long-lasting loads of more than 120 minutes.

Glycolysis - breakdown of glucose

Glucose, the main breakdown product of carbohydrates, is stored in the human body in the form of glycogen in the liver and muscles. At the average active people includes the Storage about 250-300 g Glycogen im muscle and 100-150 g in the liver. Through sport, v. a. Endurance performance, the capacity of the muscle can be increased up to 600 g. Because glycogen is important for long-term athletic performance, runners try to fill up their stores as completely as possible as part of a competition diet in order to benefit as much as possible from this energy source during the race (see nutrition during competitions).

Muscle glycogen is so important because it is for the Energy supply can be used. For this it is converted into the metabolically active form of glucose, the Glucose-6-phosphate, converted and over several metabolic steps (Glycolysis) to Pyruvic acid (pyruvate) reduced. Depending on the oxygen supply, the intensity and duration of the exercise, two different paths can then be taken.

A. Anaerobic glycolysis - breakdown of glucose when there is a lack of oxygen

Short term (20-90 seconds to a maximum of two minutes) ATP is obtained mainly from anaerobic glycolysis. Pyruvate obtained from glucose is broken down into lactic acid (lactate). In this reaction arise 2 moles of ATP - a rather lower energy yield. However, the modest contribution is made up for by the high speed. Compared for more effective aerobic glycolysis runs the anaerobic variant twice as fast from. However, with this metabolic pathway, the lactic acid concentration in the blood increases in the long term (lactic acidosis). As a result, the pH value in the muscle drops, which in turn inhibits important enzymes in muscle contraction. The result is a burning sensation in the muscles and rapid fatigue. Because of these consequences, very intense sporting activities, such as sprints, cannot be carried out over a longer period of time.

B. Aerobic glycolysis - breakdown of glucose in the presence of oxygen

With prolonged exposure over 2 minutes increasingly sets the aerobic glycolysis a. First, however, (between 2-8 minutes) a Mixture of anaerobic and aerobic energy supply. Only with somewhat longer movements (over 8 minutes) eventually outweighs the aerobic glycolysis. Oxygen is now increasingly used to metabolize glucose. Glucose initially increases even with aerobic glycolysis Pyruvate reduced. However, this is not followed by conversion to lactic acid, but further degradation Acetyl-CoA. Acetyl-CoA is completely broken down into water and carbon dioxide in several steps (in the citrate cycle), with energy being released in the form of ATP. From a molecule Glucose can be used in aerobic glycolysis 32 moles of ATP that is 30 moles more than with the anaerobic route! From an energetic point of view, this metabolic pathway is very effective if the high effectiveness is also at the expense of time.

Lipolysis - fat loss

A low exercise intensity and a long exposure time (from 120 minutes) are the essential prerequisites for the body fat uses to generate energy. As a result, the energy stores (glycogen) that can be mobilized more quickly are spared and are available for short-term use, e.g. B. Sprints are available. Even when the glycogen stores are exhausted, the body switches to the fat reserves. The fat (more precisely: the triglycerides) is released from the stores and gradually penetrated Enzymes (lipases) degraded to acetyl-CoA. Acetyl-CoA can be introduced into the citrate cycle, as it corresponds to an intermediate product of this metabolic pathway. The breakdown of a fatty acid provides approximately 107 moles of ATP, a large amount of energy. The breakdown of fats brings in even more energy than that of carbohydrates. The downside is that fat loss takes more time and more oxygen at the same time. However, because the lungs have limited oxygen uptake, the bottom line is that fat breakdown is less effective than breakdown of carbohydrates.

Fig .: Types of energy generation depending on the duration of exposure II (modified from Leitzmann, 2009)

Nutrients: how much, what and when ...

The body is in Resting carbohydrates and Fats to about equal parts used for energy generation. For this purpose, the muscle mainly uses glucose from the blood and fatty acids from the adipose tissue. At intense exercise the ratio of the nutrients used shifts towards the carbohydrates (muscle glycogen). At low and medium intensity is the proportion of Fat burning elevated. In exceptional cases, such as in hunger situations (i.e. when there is an absolute lack of energy) and a lack of carbohydrates, muscle proteins can also be tapped to provide energy. The breakdown of muscle protein is of course disadvantageous, as it is in stark contrast to the athlete's desire to improve performance. It is therefore undesirable. In order not to get into this situation in the first place, athletes should ensure that they have a sufficient supply of energy with a sufficient proportion of carbohydrates.

When which energy source is used in sport ultimately depends on the environmental conditions (duration of exercise, stress profile, oxygen availability, stress intensity, etc.), the physical constitution and the metabolism of the athlete.