European Journal of Physical Education and Sport Science
ISSN: 2501 - 1235
ISSN-L: 2501 - 1235
Available on-line at: www.oapub.org/edu
Volume 3 │ Issue 2 │ 2017
doi: 10.5281/zenodo.345745
SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC
AND ENERGY FEATURES, CONTRACTION
INTENSITY AND STRENGTH
Ratko Pavlović¹i, Kemal Idrizović ,
Stanislav Dragutinović ,
Bojan Bjelica¹, Marko Joksimović¹
¹Faculty of Physical Education and Sport,
University Of East Sarajevo, Bosnia And Herzegovina
²Faculty of Sport and Physical Education,
University Of Niksic, Montenegro
³Faculty of Mathematics and Science Education,
University of Mostar, Bosnia and Herzegovina
Abstract:
Good knowledge of functions and specific features of a muscular system enables
working with athletes in a facilitated, more professional, more quality and safer manner
as well as solving issues regarding qualitative use during the training process.
Knowledge of the features, legality of skeletal muscles and their functions enables
setting grounds for different hypotheses when the issue is athletic sports, and top
performances for which we find answers. Accordingly, knowledge of the mentioned
muscular features and marks is crucial for every subject whose work is related to sports.
Only with a proper knowledge of the legality of the active part of locomotor system, it
is possible to implement modern cybernetic models and transformational training
processes not only within athletics, but other sports branches as well. This paper
analyzes certain physiological legalities, mechanisms and energy processes of muscular
contraction.
Keywords: muscular contraction, functioning mechanisms, muscle energy
Copyright © The Author(s). All Rights Reserved.
© 2015 – 2017 Open Access Publishing Group
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Ratko Pavlović, Kemal Idrizović, Stanislav Dragutinović, Bojan Bjelica, Marko Joksimović
SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
1.
Introduction
From the aspect of athletics and other sports, it is necessary to be familiar with the core
of physiological, bioelectric and energy features of muscles. The simplest sprint start in
sprinting disciplines, long jump, high jump, shot put, various athletic running
disciplines, etc. cause certain changes in the athlete's organism. Those changes are first
visible on a cell level, then tissue, organ and, eventually, organ systems. These changes
are mostly latent. Not before performing a movement (start running, object lifting,
jumping) does this latent feature transform into a manifestation of muscular work that
can clearly be seen, based on which a certain value can be measured (running speed,
throw length, jump length and height, etc.). One must understand certain legalities of
muscular-nervous system functioning well so that they could easier understand top
performances that are achieved in athletics (Bolt, 9.58 sec – 100 m), overcoming the
boundaries of realistic human abilities Pavlović,
. Basic physiological features of
muscles are: stimulus, stimulus conductance and contractility. Due to bioelectric and
biochemical processes, muscles contract, which creates a certain amount of force. The
amount of the force created which muscles use on their adjoints depends on the number
of simultaneous active motor units and their action potentials Draga:,
. Muscle
strength factors of a movement are the size of the cross-section of a muscle, the ability to
activate the maximum number of motor units, the ability of the organism to send nerve
impulses, neural muscular coordination (composition of energy matters), bone lever
types, temperature Stojiljković,
Pavlović,
.
All skeletal muscles are innervated through branches of motor nerves and their
innervation depends on the place of muscles and nerve cell positions. In certain normal
conditions, one motor neuron can send its impulses through its neurites onto a high
number of muscle units, from 10 (eye, fingers) all the way to 100 and above (postural
musculature). Every muscle fiber that innervates one neuron is called motor unit
(mion). The number of mions differs in various muscles, thus muscles used for finer
movements have a lower number of mions than those used for musculature
maintenance (stato musculature). If greater force needs to be used or muscle contraction
speed increased, then a higher number of motor units is included in the movement,
which depends on the CNS that extraordinarily controls and coordinates work of all
skeletal muscles (Stojiljković,
.
One of the basic physiological features of a muscle cell is contractility, which
occurs upon stimulus transferred through nerves. All those nerve fibers end up in a
muscle as a sort of a spread called motor plate, and represents the so-called peripheral
synapsis, i.e. a meeting point of a nerve cell axon with muscle fiber or a meeting point
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SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
of two nerve cells. Synapses can be excitational (stimulating) and inhibitory (breaking)
and perform the impulse transfer from the nerve to muscle fiber. This arises a question
of how does it work on a cell level, all the way to the reaction of a certain muscle group?
Figure 1: The innervation of skeletal muscle – MION
For instance, in athletics while performing a sprint start, a huge reaction speed is
created (120-150 ms) which is the consequence of a well-functioning neural muscular
system of an individual (T. Montgomery, 104 ms). Motor neural fiber (neurite) before
contacting the muscle fiber loses its myelin sheath and splits like tree roots that contact
the wrinkled surface of a muscle fiber membrane, which provides a greater contact
surface. Neurite end is covered with a presynaptic membrane, in which vesicles there is
the transmitter acetylcholine which only helps perform excitation. When the bioelectric
stimulus of a neurite end occurs, the vesicle is sprinkled and the transmitter spills into a
synaptic crack. By prinkling one vesicle, around 10.000 acetylcholine molecules are
released, which is attached to protein receptors penetrating altogether through the
muscle membrane. The transmitter and receptor tying process lasts several milliseconds
which is enough to open ionic channels for entrance (Na+) into the cell (negative
charge), during which an action potential occurs (lasts 2-4 ms). At the same time,
potassium ions egress (K-) which interrupts the interaction on the cell membrane, which
creates a potential difference between the outer and inner side of the membrane that is
negative (-90mV) and starts growing to 0mV, transitioning to a positive state (+50mV),
Astrand & Rodahl,
Nikolić,
, Pavlović,
. This positive ion entrance
process and negative ion egress is called depolarization. Depolarization wave speed of
the skeletal musculature amounts to 5 m/s. The interruption of a depolarization wave
closes the entrance channels (Na+) into the cell and its prompt elimination initiates by
activating a sodium-potassium pump which spends a significant amount of energy.
When the cell membrane is being depolarized, muscle cell cannot be stimulated for 1-3
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Ratko Pavlović, Kemal Idrizović, Stanislav Dragutinović, Bojan Bjelica, Marko Joksimović
SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
ms, and that period is called the absolute refractive period. Muscular contraction occurs
after that (Fig. 2).
Figure 2: The bioelectric processes in the muscle cell
2. Mechanism of muscular contraction creation
The process of initiating muscular contraction is related to the process of muscle cell
depolarization. Immediately after that begins the process of repolarization, along with
which start myofibril sliding and the initiation of muscular contraction. As a constituent
part of myofibril (contractile elements) four proteins participate, which are responsible
for muscular contraction. These are thick myosin fibers, somewhat thinner actin fibers,
tropomyosin with elongated molecular composition and troponin with its three parts: I,
T and C; T and C are so-called regulatory proteins that perform the opening of ionic
channels for entrance of Na+ into the cell. These proteins are parallely placed along the
cell and are closely bonded to the cell membrane where there are up to several
thousands of them in each cell (Draga:,
Pavlović,
. Myosin component
consists of body and head whereas actin consists of a round-shaped protein, i.e.
globules that are grouped in long chains spirally twisted around their longitudinal axis.
Thin actin fibers are tightly bonded to a Z-disc and one of its part is situated parallely
between thicker myosin fibers. Actin fibers are only a few microns thick and are
grouped around the thicker myosin fiber. That relation is 1:6, which means that six actin
fibers are grouped around one myosin fiber. These two proteins and round plates called
Z-discs (Z-lines) comprise the basic myofibril structure. Myoglobin is placed around
myofibril, it is similar to hemoglobin, red and bonds oxygen to itself. Myoglobin is
more common with red muscle fibers that contract slower because of the allevated
presence of O2 in relation to white Bajić and Jakonić,
.
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Ratko Pavlović, Kemal Idrizović, Stanislav Dragutinović, Bojan Bjelica, Marko Joksimović
SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
Figure 3: Sarcomere - relaxed and contracted the condition
The space between two Z-discs is called sarcomere, where brighter spaces on sarcomere
create actin, and darker create myosin. While muscles are in a standstill, in this area
actin and myosin fibers do not intertwine but there is a contraction this area disappears.
Thicker myosin fibers have a part of molecule that is called head which is consisted of
four smaller, ordered in a thorn-like manner across one semi-circle with an exact
spacing. There is a theory that the actin surface has indents inside which myosin heads
prowl, at which time they make a movement similar to rowing, moving actin fibers
towards the inside, which also moves Z-discs, thus performing a contraction. During
the contact with actin, not all four heads of meromyosin participate, but only one,
which depends on the used muscle force. If greater muscle constraint is needed, and
there is a longer excitation of neural muscular synapsis, then two, three or even four
meromysin heads participate in the contact (Astrand & Rodahl, 1986). The energy for
pulling actin fibers in is secured with solving ATP, while regulatory proteins troponin
and tropomyosin together with Ca are responsible for the initiation of sliding actin
fibers.
Muscles mostly create a certain muscle force of higher or lower intensity. As a
consequence of manifestation of force of certain intensity, muscle contractions that
perform mechanical work are created (jump, rebound, lift, sliding move, run, etc.).
Accordingly, muscular contraction can be twofold in relation to the force generated by
the muscle and forces which muscle force opposes to. When force sizes are equalized,
muscle barely shrinks during which isometric contraction occurs. Contraction which
changes muscle length is called isotonic contraction during which mechanical work
occurs. Contraction which approximates muscle adjoints is called concentric or
myometric, and when muscle adjoints separate excentric or plyometric contraction.
Based on these changes, all cyclic and acyclic athletic movements are performed
Kukolj,
Stojiljković,
Pavlović,
.
Skeletal muscles are tense even when standstill. That tension is considered a
basic degree of contraction of skeletal muscle called muscle tonus. Tonus is a
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SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
physiological characteristic of a muscle and represents the lowest degree of muscle
tension that can be maintained for a long time without fatigue occurrence. Although for
a long time there has been a dilemma whether it is tonus of central origin or
consequence of collection of liquids in muscles after work and fatigue occurrence, it is
still proven that the it is of central origin as it occurs in the sleeping phase when muscle
constantly sends impulses about the stretching state across tendons and joint capsules
in sensory areas, and CNS uninterruptedly sends back corresponding signals to muscle
fiber Pavlović,
. One of the muscle characteristics is its elasticity. On average, a
muscle can be stretched to one third of its normal length and as we get older muscle
elasticity decreases and reduces muscle tonus (Fitts, 1994). Depending on the muscle
fiber type, numerous physiological processes in them will also depend, for instance
contraction time, fatigue resistance, energy source, mononeuron size, etc. (Figure 1). In
athletic disciplines the fast, explosive, powerful and exact movements dominate. The
manner of movement manifestation depends on the discipline. Sometimes it is
important to lift a huge weight (weight lifting), sometimes to throw to a certain length
(discus, shot, hammer, javelin), and sometimes to jump as farthest or as highest as
possible. However, it all depends on the muscle type, and mostly on the muscle
contraction intensity and strength. To better understand this issue, muscle behaviour
and some of its specific features it is crucial to understand the legalities of muscle
functioning, i.e. muscle contraction intensity and strength.
Table 1: Characteristics of muscle fibers (Fitts, 1994)
Type of fiber
Slow I
Fast IIA
Fast IIB
The time contraction
slow
fast
very fast
Size of motoneurons
small
big
very large
Fatigue resistance
high
median
small
The activity
aerobic
Anaerobic-long
anaerobic-short
Production of forces
small
big
very large
The density of mitochondria
big
big
small
The density of capillaries
big
median
small
The oxidative capacity
big
big
small
Glycolytic capacity
small
big
big
The main source of energy
triglycerides
CP, glycogen
CP, glycogen
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Ratko Pavlović, Kemal Idrizović, Stanislav Dragutinović, Bojan Bjelica, Marko Joksimović
SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
Table 2: Percentage ratio of the diameter of the fiber m.quadriceps hamstrings in
both sexes of different ages Perić,
Size cross section (micrometer²)
Typ
Percentage distribution
of fiber
Male
16. years
Female
20-30. years
16. years
20-30. years
I (SO)
52
4880
5310
4310
3948
IIA (FOG)
33
5500
6110
4310
3637
IIB (FG)
14
4900
5600
3920
2235
70
10
45
25
Number participants
3. Muscle contraction intensity and strength
The final common denominator in sports competitions is: what can muscles do? How
much intensity can they develop when it is needed, how much strength can they
produce during the performance of work and how long can that activity last?
Certain phases of muscle contraction intensity as well as changes that bring it up
can be seen using the special instrument, kymograph. On the acquired myogram phases
of muscle contraction can easily be seen. “It“ first starts with latent period or hidden
period of contraction, then contraction occurs (muscle shrinking) and finally releaving
phase and decontraction. During the latent period, changes already described occur:
bioelectric processes on membrane, entrance of Na+, releaving of K++ ion, etc.Muscle
shrinking process occurs when actin and myosin myofilaments slide. Muscle generally
constracts only under influence of series of impulses, but not individual impulse which
brings up permanent muscle shrinking, i.e. tetanus contraction
Stojiljković,
Pavlović,
Perić,
Draga:,
. Depending on the number of impulses,
muscle contraction can be performed as a smooth tetanus or serrated tetanus. If muscle
contraction is of a smaller intensity and lasts longer, smooth tetanus occurs, but if
muscle contraction is of a higher intensity and lasts in a short period of time, serrated
tetanus occurs due to fatigue occurrence, i.e. reduced amount of transmitters on the
periferral synapsis. Tetanus contractions are four times stronger than individual ones
because they are a consequence of high number of stimuli even up to 50/sec. The only
body muscle that contracts with an individual muscle contraction is cardiac muscle.
Regarding muscle contraction, is interesting that the muscle contracts in accordance to
the all or nothing law. It means that, if contraction occurs, muscle shrinking will always
be maximum depending on the muscle type. Differently put, muscle reacts to a
stimulus with a maximum shrinking or does not react to it at all if it is below the
stimulus threshold, which depends on the membrane potential Bajić and Jakonić,
1996).
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SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
a
e
b
Figure 4: The contraction of tetanus: a) incomplete; b) complete
These changes can be analyzed on the example of sprint start in athletics. After the
starter pistol goes off, we perceive the signal through our hearing apparatus (receptor)
that informs the athlete about the new outside stimulus. This starter signal is
transferred via sensomotor afferent paths and processed in certain CNS zones as a
signal for starting performing muscle work. The muscle undergoes bioelectric changes,
first on a cell level (process of action potential and depolarization), which are the first
prerequisites for initiating myofilament sliding. On the basis of cell changes,
myofilament sliding occurs which leads to shortening (lengthening) of muscle fibers,
bundles and eventually entire muscle which as effector performs mechanical work with
necessary energy. Not before that does stretching out, i.e. pushing of the athlete off the
start blocks occurs and start acceleration initiates. Those reaction speeds are small (T.
Gay 136 ms).
Muscle contraction strength is demonstrated in multiple ways. Sometimes we are
able to perform easier tasks, such as lifting a very light object (pencil, rubber, bag, etc.),
and sometimes even a heavy object (weights). These and other similar activities use the
same muscle groups that do the same work. These activities have a different character
and intensity that depends on the weight size. This weight size is directly proportional
to the number of active motor units, which means that if the weight is smaller, a smaller
number of motor units is used, unlike bigger weights when a bigger number of motor
units is used. Each movement is precisely controlled, where indicators could be
movement amplitude size, movement speed, movement frequency, number of
repetitions, etc. Strength of this contraction is performed in different centres of cerebral
cortex, spinal cord through different receptors, proprioreceptors, ligaments, joints,
muscles Nikolić,
. Each data is processed in main nerve centers that process the
delivered data and send an adequate reply, which can even be a correction to the
received signal. The main role in the control of muscle contraction size has specific
muscle fibers, so-called intrafusal muscle fibers or muscle spindle (IF) that act as sensors
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SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
Stojiljković,
. Each muscle has a certain number of intrafusal fibers, depending on
the muscle type. Muscles that perform manipulation movements are rich with this IF
musculature, even up to 30 IF muscles on 1 gram of body mass, while postural muscles
(m. latissimus dorssi) and other are less rich in comparison. The IF fibers are situated
parallely to all muscle fibers, and their ends are bonded with tendons. Work principle
of sensory fibers is the feedback principle. When muscle straining occurs, the middle
part of intrafusal musculature is stretched which sends impulses on that change to
spinal cord where there motor cores of that muscle are stimulated and it contracts. This
is the case with muscle contraction. However, when a certain weight is to be lifted there
is an opposite reaction; intrafusal musculature ends stretch first, and then the entire
musculature. These contractions are precisely dosed in accordance with the weight size.
Muscle contraction strength also depends on the number of muscle fibers active
in a muscle activity. Number of muscle fibers is genetically predetermined, so some
persons have more muscle fibers than others, and thus are stronger. For example, if we
compare two non-training persons, same age, same weight and height, i.e.
morphological status where under the same condition one can lift 80 kg bench press,
and the other cannot, a question arises: how is that possible? It means that the person
who lifted 80 kg has a genetically better muscle tissue structure, i.e. higher number of
muscle fibers (myofibrils) which perform muscle contraction Pavlović,
. This rule
is not applicable to persons undergoing training, because high strain causes
accumulation of muscle fibers by consuming certain proteins through food. However,
persons with a higher number of muscle fibers can be at an advantage. Apart from that,
muscle contraction strength influences condition of muscles, fatigue and types of
muscles performing work (Fitts, 1994). It is considered that the strongest muscles in
human body are those which oppose the effect of gravity, enable human body to
maintain upright posture (neck, back, pelvis, quadriceps). If the contraction conditions
are the same, i.e. muscle stimulus, temperature, muscle fatigue, then muscle contraction
strength can depend upon the initial muscle length before the contraction. If a muscle is
stretched to maximum, it has less contraction strength than if it were only slightly
stretched. This is the reason it is best to work with the optimal muscle stretch.
Maximum strength can be expressed in maximum weight a muscle can lift. It can be
very high, and can even be multiple times higher than the body weight (according to
Russian authors even 7 kg/cm2) of the cross-section (i.e. m. gluteus maximus 1200 kg).
For instance, foot muscles do not only carry the body weight, but even the weight a
person carries on their back. Human skeletal muscles are capable of achieving pressure
strength of 3-4 kg/cm2 (Guyton, Hall, & Saunders, 1999). It is counted based on
anatomic and physiological cross-section of a muscle. Anatomic cross-section is the
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SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
cross-section of fibers under the 90° angle in relation to the longitudinal muscle axis,
whereas physiological cross-section is the cross-section perpendicular to the course of
certain muscle fibers. Spindle shaped muscles have different cross-sections, whereas
other muscle types (feather, square, deltoid) have a much higher physiological crosssection Pavlović,
.
Table 3: The microstructure and biochemical changes in muscle fibers that occurred under the
influence of training of various types of motor skills (% change from the initial level)
(Yakovlev, 1983)
Parameters
Endurance
Speed
Strength
Relative muscular mass% of the total body weight
9
32
39
Cross section, the thickness of the muscle fibers
0
24
30
60
30
-
Sarkoplasma reticulum
5
54
60
Myofibril
7
63
68
23
57
30
0
18
59
Myoglobin
40
58
-
CP
12
58
53
Glycogen
80
70
38
0
15
53
The number of mitochondria per surface section MJ
The protein content
Sarkoplasma
Myosin
Receiving via reticulum Ca
Phosphorylase
23
40
20
230
100
-
Speed glycolysis
10
56
28
Speed oxidation
53
45
20
Oxidative enzymes
During the training process and the competition, especially characteristic for athletics is
the state of a well prepared organism, muscular and other systems of the organism that
will function the best in conditions of hard work.
Muscle contraction strength depends on the initial muscle length (stretchedness),
type of lever to which a muscle is attached to, muscle fatigue, organism temperature,
sex, age, etc. The optimum initial muscle strechedness is the best for performing any
type of work. Contraction strength depends also on the lever to which a muscle is
attached. The higher the lever force tentacle, the less strength is needed for its
movement and vice versa. Greater muscle force is needed if the work is done using one
joint (Mc Ginnis, 1999). However, most movements inside the organism are performed
using two or more joints, so the contractions are smaller in relation to the force used,
which saves energy than if two or three muscles were to be engaged Jovović,
. If
fatigue occurs, energy-generators that cause muscle contractions are reduced. Elevated
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SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
body temperature over 37.5°C affect negatively on muscle contraction and force usage
so not any activity is recommendable during that period. This is especially important
during the training process when strains are supraliminal aiming at transformation of
certain abilities. In relation to men, women have 70% slow (red) and around 80-85% fast
(white) muscle fibers (Miller & Tarnopolsky,
Perić,
Pavlović,
. The
amount of body mass is also smaller on women, which means they can only use 65-80%
force in relation to men of same age and same physique. Nonetheless, let us not
misunderstand the fact that, though the structure and physique are the same, under
certain circumstances and controlled training women can get achieve higher results,
approximating to those men achieve Nikolić,
.
Table 4: Schedule of red fibers in some muscles obtained autopsy (Nikolic, 1995)
Muscle
% red fibers (range)
Male
Female
m.quadriceps fem., vastus lateralis
40-65
35-40
m. rectus femoris
38-50
30-55
m.gastrocnemius
40-58
40-65
m.tibialis anterior
65-80
57-80
75-100
85-90
m.deltoideus
43-80
55-70
m.biceps brachii
38-60
60-70
m.triceps brachii
15-50
35-40
m.longissimus dorsi
56-60
58-62
m.soleus
4. Muscle contraction energy
Athletic disciplines demand from an athlete a high energy consumption during the
performance of an activity. As a consequence of consuming energy, certain work
occurs. There is no greater strain for a body than strain during heavy muscle work.
Actually, if heavy muscle work would last longer, it could be deadly. Here is one
example in athletics: if a man has high temperature which could be deadly, body
metabolism increases for about 100% above normal. Comparatively, metabolism of an
athlete who runs marathon increases for about 2000% above normal (Guyton, Hall &
Saunders, 1999).
To better understand this issue, we will take a look at a manner securing and
consuming energy. Human organism functions like a machine which uses certain fuel,
i.e. energy to work. They gain that energy in a form of chemical compounds,
transforming it into free energy that performs mechanical work. The main source of
energy is carbohydrates, fats and proteins which secure that energy for muscle
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SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
contraction with certain biochemical processes (metabolism). The main source is the
highly energetic compound adenosine triphosphate (ATP), consisted of nitrogen base of
adenine, pentose sugar of ribose and triphosphate group Pavlović,
. The first
phosphate group is tied to ribose with a stable bond making the compound adenosine
monophosphate (AMP). This compound is not rich with energy. By adding another
phosphate group, another stable bond adenosine diphosphate (AMP+P=ADP). By
bonding the last phosphate group, an unstable, easily broken bond occurs, adenosine
triphosphate (ATP) but which is rather rich with energy. While releasing one phosphate
radical, ATP frees 7-9 Kcal or around 30-36 KJ (kilojoules) of energy per one molecule
and that energy is transferred to a new compound, creatine phosphate CP Bajić and
Jakonić,
Stojiljković,
. The amount of ATP in muscles, even in trained
athletes, is enough to maintain maximum strength for only around 5-6 seconds, which
can be enough for a 50 m sprint (Guytop, Hall, Saunders, 1999).
All these bonds are reversible, and their transfer is performed with help from
certain enzymes. It means that ATP can be dissolved to ADP, ADP to AMP and again
return to the prior state of ATP depending on energy. In muscle cells, amounts of ATP
are limited, so they have to be restored constantly. Another compound found in muscle
cells which is capable to be bonded to a phosphate group is creatine (C). When a cell is
in standstill, ATP gives one phosphate group to creatine and phosphorizes it, the result
of which is creatine phosphate (CP). During muscle work, creatine phosphate is
dissolved and again frees phosphate radical which is bonded to ADP through enzymes
and again creates ATP (Yakovljev, 1983; Volkov, 1986; Sahlin, 2010). In the moment of
relaxation and receiving the phosphate radical, a huge amount of energy is released and
is used for muscle contraction, and also transforms into other shapes of energy, thermal,
mechanical, bioelectric. This energy is also gained by dissolving carbohydrates (CH)
using glycolysis and Krebs cycle processes, fat and protein. Regarding CP reserves are
limited, it can secure energy that can last for 8-10 seconds, so it represents the main
energy source for extremely fast and explosive activities in athletics such as 100 m
sprint, jumping and throwing disciplines (Guyton, Hall, Saunders, 1999). Namely,
renewing creatine phosphate is happening fast, and in the first 30 seconds achieves 70%
and in the period from 3 to 5 minutes 100%. In more intensive disciplines that last
approximately 40 seconds (200 m, 300 m, 400 m sprint), ATP-CP composition first
secures energy, and after 8-10 seconds includes the lactic acid composition (Janssen,
2001).
European Journal of Physical Education and Sport Science - Volume 3 │ Issue 2 │ 2017
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Ratko Pavlović, Kemal Idrizović, Stanislav Dragutinović, Bojan Bjelica, Marko Joksimović
SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
Figure 5: The transport of energy
Inside it, glycogen from muscle cells and liver is dissolved, releasing energy for
resynthesis of ATP from ADP+P. Due to lack of oxygen, a side effect occurs, which is
well-known as lactic acid. During high intensity activities, it causes accumulation inside
the muscle which causes fatigue and ultimately the end of physical activity. Renewing
this lactal composition demands longer period of time, it can last for days and depends
of the type of training and nutrition of the athlete. For example, with moderate intensity
activities (interval training), to renew 40% of amount 2 hours have to pass, for 55% 5
hours and for 100% 24 hours are needed. Parallel to this, it is necessary to extract lactic
acids from blood, which needs more time, 10 minutes to remove 25%, 25 minutes for
50% and an hour and 15 minutes for 95%. Unlike anaerobic composition, aerobic
composition is dissolved by glycogen in the presence of oxygen producing little or no
lactic acid, enabling the athlete to continue the activity. Aerobic composition is the key
energy composition for disciplines that last between 2 minutes and 2-3 hours, 1500 m,
long track Nikolić,
.
Table 5: The energy for some track and field events (Nikolic, 1995)
Discipline (m)
Energy transport (kJ)
Discipline (m)
Energy transport (kJ)
100
231
3.000
1.176
200
294
5.000
1.890
400
420
10.000
3.150
800
546
30.000
7.560
1.500
714
42.195
10.500
European Journal of Physical Education and Sport Science - Volume 3 │ Issue 2 │ 2017
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Ratko Pavlović, Kemal Idrizović, Stanislav Dragutinović, Bojan Bjelica, Marko Joksimović
SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
Table 6: Activities maximum intensity varying duration and processes providing energy for
these activities (Janssen, 2001)
Duration
1-5 sec
6-8 sec
Type of
Ensuring of
process
energy
Note
anaerobic
alactate
ATP
does not create lactate
anaerobic
ATP + CP
does not create lactate
alactate
anaerobic
9-45 sec
alactate +
ATP + CP + muscle
anaerobic
glycogen
lactate
45-120 sec
anaerobic
lactate
big lactate production,
muscle glycogen
with an extension of the duration of the activity is
reduced lactate production
anaerobic
2-4 min
lactate +
muscle glycogen
aerobic
4-10 min i
dalje
aerobic
muscle glycogen
with an extension of the duration of the increased
+ fatty acid
fat content
Table 7: The relative proportion of aerobic and anaerobic processes resynthesis of ATP in the
overall energy balance of disciplines (Bajic and Jakonić,
% the aerobic release
% anaerobic release
The limit time
Distance
The character of
of energy
of energy
contest (min)
(m)
work
100
0
135,00
42195
90
10
29,00
10000
80
20
14,00
5000
70
30
60
40
8,00
3000
50
50
4,00
1500
40
60
2,50
1000
30
70
1,75
800
20
80
0,75
400
10
90
0,35
200
0
100
0,15
100
Aerobic
Aerobic
Anaerobic
Anaerobic
Regarding participation of aerobic and anaerobic processes of resynthesis of ATP in
balance of athletic disciplines, we can see inverse relationship of these abilities (Fig. 7).
Aerobic processes comprise long track activities (5,000 m to marathon) and here they
have an 80% (AE) : 20% (AN) ratio, unlike running disciplines (1,000 to 3,000 m), where
the ratio is 40-60% (AE) : 60-40% (AN). At the end, sprinting type disciplines (100 m to
European Journal of Physical Education and Sport Science - Volume 3 │ Issue 2 │ 2017
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Ratko Pavlović, Kemal Idrizović, Stanislav Dragutinović, Bojan Bjelica, Marko Joksimović
SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
800 m) have a ratio of 30% (AE): 70% (AN). Knowledge of these ratios of AE and AN
potentials is crucial in planning training as well as energy intake through food.
5. Conclusion
This paper analyzed basic postuplates regarding functioning of skeletal muscles while
performing physical activities with the genesis of certain processes origin in the
organism on a relation CNS – muscular system. Bioelectric and physiological changes
process has been defined from the cell level all the way to the huge muscle system.
Understanding how the organism functions from the first nerve impulse to the last
response of a muscle regarding muscle contraction is important in order to learn,
observe, plan and manage in a training process with young athletes. Also, defining
muscle contraction intensity and strength will largely enable clearer understanding of
muscle system functioning and eventual undesired consequences that can occur as a
consequence of unprofessional work of an individual. The importance of energy of
muscle contraction is also emphasized in performing mechanical work and its
renewability. Energy function of muscle activity is significant for balance of aerobic and
anaerobic processes in energy balance of athletic disciplines and overall muscle work.
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SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
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CONTRACTION INTENSITY AND STRENGTH
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Ratko Pavlović, Kemal Idrizović, Stanislav Dragutinović, Bojan Bjelica, Marko Joksimović
SKELETAL MUSCLES: PHYSIOLOGICAL-BIOELECTRIC AND ENERGY FEATURES,
CONTRACTION INTENSITY AND STRENGTH
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