This document contains all information obtained from the lectures. It is written in a clear structure and contains all relevant information. Furthermore, the document elaborates on the article on fluid homeostasis from Jeukendrup which is also important for the exam.
Faculty of Health, Medicine and Life Sciences
Human Movement Sciences: Sports Nutrition
2020 - 2021
,SUBSTRATE OXIDATION
CARBOHYDRATES AND GLYCOGEN
Carbohydrates are considered saccharides and several forms of saccharides exist.
Monosaccharides include glucose, fructose and galactose. Disaccharides includes
maltose, sucrose and lactose, whereas polysaccharides include starch, cellulose and
glycogen.
When polysaccharides are ingested, they first need to be broken down to
monosaccharides before it can be absorbed. These can then either be used to produce
energy, or it can be stored as glycogen in muscle and liver.
1) Glucose enters the muscle or the liver by GLUT2/4 upon either muscle
contraction or insulin secretion.
2) Upon entry, glucose is converted into Glucose-6-phosphate by an enzyme called
- Glucokinase in the muscle
- Hexokinase in the liver
3) When glucose-6-phosphate is converted into Glucose-1-phosphate, to uridine diphosphate glucose, then it is converted
into glycogen.
4) Then glycogen is stored.
This pathway is activated the other way around when the energy source is needed as glucose. This is the oxidation pathway and
is called glycolysis.
The muscle lacks the enzyme Glucose 6-phosphatase. The liver does have the enzyme glucose-6-phosphatase. Therefore, it is
only possible to convert glucose-6-phosphatase to glucose in the liver. An explanation for this process might lay in the fact that
most of the energy is actually needed in the muscle itself! The muscle does not aim to export the energy out of the muscle. The
liver does, therefore, the expression of glucose-6-phosphatase in the liver seems logic.
2 pools for glycogen synthesis exist in the muscle called Proglycogen and macroglycogen. Proglycogen is predominantly stored
during the first phase of recovery and depends on the amount of carbohydrates that are ingested during this period. During the
second recovery phase, the macro glycogen pool serves are refilled. Macroglycogen has an increased amount of glucose bound
to the glycogenin core. The increase in the macroglycogen pool appears to be related to the “super-compensation” in the
muscle such as 2-3 days after eating a lot of carbohydrates.
LIPIDS AND ADIPOSE TISSUE
Adipose
Adipose tissue deposition differs between 5-60% of our body mass and differs in
visceral fat and subcutaneous fat. Visceral fat is mainly located around the organs
and subcutaneous fat is deposited where it is more visible, the belly, inner thighs
and glutes. Furthermore, fat can also be stored in muscle.
- SAT: subcutaneous fat
- IMAT: intermuscular fat
- IMF: intermyofibrillar fat
- IMCL: intramyocellular lipids (IN the muscle cell).
Lipids
Lipids consist of triglycerides that are broken down before being absorbed.
Triglycerides are split into glycerol and three fatty acid molecules, which are used for
energy or stored in adipose tissue and in lesser extend in the muscle.
The conversion of a triglyceride into glycerol and free fatty acids demands for the
presence of 3 H2O molecules and a catalyst. The reaction can be seen in the figure on
, the next page. Both glycerol and fatty acids are used in the mitochondria to
produce energy. Fatty acids can be divided into saturated (no double bonds)
and unsaturated (double bond, poly-unsaturated: multiple double bonds) fatty
acids. A cis-double bond indicates that the H-atoms are located at the same
side of the carbon molecules. Trans-bonds are the opposite.
PROTEINS AND MUSCLE
Skeletal muscle is the storage place for protein and its anatomy starts with the
muscle itself, containing many fascicles, fascicles contain a lot of muscle fibers
and a muscle fiber contains a lot of myofibrils. Myofibrils contain the structural elements of the muscle that allow for muscle
contraction to occur: actin an myosin. When the muscle relaxes, actin and
myosin filaments do not overlap each other. Upon contraction, ATP and Ca 2+
are provided and actin and myosin slide over each other, aiming to produce
force. The rate and the amount of force that is produced, depends on the fiber
type. Characteristics of each fiber type are shown in the table below.
ENDOGENOUS ENERGY SOURCES
Endogenous energy sources are stored within the human body, in contrast to
exogenous energy sources, which are consumed via the diet. Substrates that are
used for energy are carbohydrates, fats and proteins. Substrates that are mainly
used are carbohydrates and fat, because proteins are mainly used as building blocks
of muscle rather than energy source. Organs in which these fuels are stored are the
blood, liver, brain, muscle and adipose tissue. In order to use different substrates for
energy production, they all need to be converted into ATP. The efficiency in which
this occurs strongly depends on the substrate itself. The anatomy within the
myofibril already aims for an efficient ATP generation-system. Because the
mitochondria are located within/between myofibrils, therefore, ATP can be
transferred easily from the mitochondria to the place where it is needed for
contraction; the myofibril.
ENERGY SYSTEMS
There is enough ATP present for a powerful contraction up to 2 to 4 seconds. This can be explained by the fact that ATP is a very
heavy molecule, therefore, it would not be efficient to walk around with large amounts of ATP throughout the day.
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