Anaerobic Metabolism and Exercise Physiology: A Comprehensive Overview

This report provides a comprehensive overview of anaerobic metabolism within the context of exercise physiology. It begins by defining anaerobic exercise and its applications in non-endurance sports, emphasizing the role of lactate formation. The report details the two primary anaerobic energy systems: the ATP-PC system (phosphagen system) and anaerobic glycolysis. It explains the function of ATP, creatine phosphate, and their roles in energy transfer and muscle contraction, including the duration and intensity of activities supported by each system. The report then delves into glycolysis, outlining the conversion of glucose to pyruvate, the involvement of key enzymes (hexokinase, phosphofructokinase, pyruvate kinase), and the production of ATP and NADH. It also discusses the role of NADH in lactate production during anaerobic glycolysis. The report further explores aerobic metabolism, the electron transport chain, and lipid oxidation. It examines skeletal muscle structure, including the roles of epimysium, endomysium, perimysium, fascicles, muscle fibers, and myofibrils. The report describes the sarcomere and its components (Z-lines, I-band, A-band, H-zone, sarcoplasmic reticulum, T-tubules, actin, myosin, tropomyosin, and troponin). Finally, the report explains the sliding filament theory, detailing the stages of muscle contraction and the role of ATP and calcium ions, and references key sources.

Exercise Physiology
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Anaerobic metabolism:
Anaerobic exercise is an intense form of physical exercise in which lactate formation occurs.
It is generally used in non-endurance sports for promoting strength, speed, power and to build
muscle mass. Anaerobic energy systems are of two types : 1) high energy phosphates,
adenosine triphosphate and creatine phosphate; and 2) anaerobic glycolysis. Adenosine
triphosphate (ATP) is a molecular unit which performs function of intracellular energy
transfer. ATP can be used as the source of energy for the contraction during exercise. ATP
can be produced by creatine phosphate, glycogen and aerobic respiration. Creatinine
phosphate (CP) is also stored in the muscle cells like ATP. In the process of breaking down
of CP, large amount of energy gets released and this energy gets utilised for the resynthesise
of ATP. ATP can provide energy for 3 seconds on the other hand CP can provide energy for
up to 8 seconds with high rate as compared to ATP. Lifting heavy weight, sprinting fast for
50 – 100 metres and punching boxing bag hardly for 2 – 3 punches are the activities which
use ATP-PC. ATP–CP is also known as phosphagen system. Total amount of energy storage
in ATP-CP system is less, however this phosphagen form of energy can be utilized as rapid
availability of energy (Plowman and Smith, 2013).
Glycolysis:
In glycolysis, glucose gets converted into pyruvate and free energy gets released. Released
free energy can be useful for the formation of ATP and NADH (reduced nicotinamide
adenine dinucleotide). Glucose, ADP and NAD are the substrates and pyruvate, ATP and
NADH are the end products in glycolysis. Glycolysis has low capacity for about 30 seconds
to 3 minutes and high power but not very powerful. Glycolysis occurs in cytosol which is a
liquid found inside the cells. Hexokinase, phosphofructokinase and pyruvate Kinase are the
three kinases plays important role in regulation of glycolysis. Hexokinase regulates first step
which is a conversion of glucose to glucose-6-phosphate. Phosphofructokinase regulates third
step which is conversion of fructose-6-phosphate into fructose-1,6-biphosphate. Pyruvate
Kinase regulates final step which is conversion phosphoenolpyruvate into pyruvate. In
anaerobic glycolysis, NADH plays role in the production of lactate from the pyruvate.
Pyruvate is the final product of glycolysis. In this process of cellular respiration ATP gets
produced. Glycolysis is required in the weight training, sprinting, jogging, high rep swings or
snatches (Porcari et al., 2015).
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Aerobic metabolism:
Aerobic metabolism take place in the mitochondria and in this process more amount of
energy gets released. In aerobic metabolism acetyl COA, hydrogen and glucose get oxidized.
Pyruvate dehydrogenase complex oxidizes pyruvate to acetyl-CoA and CO2. In the first step,
pyruvic acid formed from the glucose and in the second step this pyruvic acid formed in the
glycolysis enters mitochondria. Isocitrate dehydrogenase is the rate limiting enzyme in the
Krebs Cycle, TCA, Citric Acid cycle. Dehydrogenase enzymes eliminate electrons from the
intermediate products and these enzymes gets transported to coenzyme NAD which result in
the NADH. Electrons can be taken to the inner membrane of mitochondria by these
coenzymes for use in the electron transport chain. Dehydrogenase is regulated by its substrate
pyruvate and product acetyl CoA. Glycolysis, Krebs cycle and electron transport chain
produces 4, 2 and 32 ATPs produces respectively. Overall in aerobic metabolism 38 ATPs
gets produced. Aerobic metabolism includes less intensity exercises which can be performed
for longer duration. It includes walking, long slow runs, rowing, and cycling. In aerobic
glycolysis, NADH transported into the mitochondria and gets oxidized to NAD (Boone,
2013).
Electron transport chain :
Electron transport chain occurs in the inner mitochondrial membrane. In oxidative
phosphorylation, ATP gets formed due to transfer of electrons from NADH or FADH 2 to O2
through series of electron carriers. Electrons get transferred from electron donors like NADH
or FADH 2 to electron acceptors like oxygen through redox reaction. This electron transfer is
associated with development of proton gradient across the membrane and transfer of protons
through the membrane. Due to this electron transfer under the influence of ATP synthase,
ATP and water produced during electron transport chain. NADH + H+ from glycolysis can
enter the ETC by entering in the mitochondria. 34 ATP molecules can be produced from
NADH + H+ and FADH2. Oxygen is the final acceptor of electron in electron transport chain.
Glycerol 3-phosphate shuttle is the shuttle for NADH + H+ (Connes et al., 2010).
Lipid oxidation :
Triglycerides are the main fat present in the blood and it is taken up in the adipose tissue
which can be used as energy for the next time. Saturated and unsaturated fatty acids are types
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of two common fatty acids. Beta oxidation is the catabolic process in which breaking of fatty
acids take place to produce acetyl-CoA. This acetyl-CoA enters into the citric acid cycle, and
NADH and FADH2. These co-enzymes are useful in the electron transport chain. 7 NADH +
H+ and 7 FADH2 molecule gets produced during beta oxidation. Remaining acetyl-CoA and
acyl-CoA enters citric acid cycle by combining with oxaloacetate to form citrate. It is called
beta oxidation because beta carbon of the fatty acids gets converted into carbonyl group due
to oxidation. One fatty acid will generate more ATP as compared to glucose when it gets
fully oxidised. Glucose produces more CO2 per O2 as compared to the fatty acids. Proteins
can be oxidised to get energy. Phosphagen pathway provides most of the energy at the start of
the exercise. Aerobic metabolism is a slow process and it utilizes carbohydrate and fat as the
energy source. Hence, it can’t be used as energy source at the start of the exercise (MacLaren
and Morton, 2011).
Skeletal muscle :
Epimysium is the layer of connective tissue in which outermost layer of the muscle fiber gets
wrapped. Endomysium is the connective tissue layer in which individual muscle fiber gets
encased inside the fascicle. Perimysium is the middle layer connective tissue which bound to
long muscle fibers of every fascicle. Fascuculus is the bundle of skeletal muscles surrounded
by connective tissue like perimysium. Muscle fibers are building blocks of skeletal muscles
and these are made up of myofibrils which contains actin and myosin filament. Skeletal
muscles are closely intertwined by blood vessels and every muscle is supplied with multiple
blood capillaries. Sarcolemma is present on the outside because it is plasma membrane and
sarcoplasm is present inside because it is cytoplasm of the skeletal muscle. Sarcomere is
section between two neighbouring Z-lines. Z-line is disc between the I bands and it is dark in
colour. I-band is the region which surrounds z-line and it is zone of thin filaments. A-band is
present after I-band and it contains single thick filament. In between A-band a paler region is
present which is called as H-zone. Sarcoplasmic reticulum is defined as special type of
smooth endoplasmic reticulum. Sarcoplasmic reticulum regulates concentration of calcium
ions in the cytoplasm of striated muscles. Transverse tubules (T-tubules) are the extension of
cell membrane which enter towards centre of the cells. T-tubules which are closely associated
with specific part of the sarcoplasmic reticulum are called as cisternae. Actin is a group of
globular multi-functional proteins which form microfilaments. Myosins are the ATP-
dependent superfamily of motor proteins which plays role in muscle contraction.
Tropomyosin is the essential part of the actin filaments which plays important role in the
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regulation of actin filaments in both muscle and nonmuscle cells. Troponin is a complex of
troponin C, troponin I, and troponin T and plays essential role in the muscle contraction.
Actin filaments are majorly present in I band and it extends upto A-band. Myosin filaments
are present throughout A-band. Actin filaments bound to the Z-line. H-zone is associated
with thick filament myosisn (Richter et al., 2013).
Sliding Filament theory:
ATP is the source of energy for contraction and relaxation. ATPase is present on myoin
protein. ATP is in mitochondria. Acetylcholine stimulates sarcoplasmic reticulum for release
calcium through the muscle which stimulates contraction. Toponin and tropomycin binds to
the calcium which makes myosin cross bridges to attach to actin which brings contraction in
muscles. Excitation signal come from the brain through nerve impulse. This excitation
potential arrives at nerve terminal and releases acetylcholine. Acetylcholine travels through
neuromascular junction which stimulates sarcoplasmic reticulum to release calcium through
the muscle. Myosin swivels and actin slides. Relaxation occurs when nerve impulse stops and
calcium gets back in the sarcoplasmic reticulum which causes breaking actin and myosin
link. According to sliding filament theory, muscle contraction occurs in four stages like
muscle activation, muscle contraction, recharging by ATP resynthesise and relaxation which
will be helpful in the improving performance of athletes (Kraemer et al., 2011).
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References :
Boone. (2013). Introduction to Exercise Physiology. Jones & Bartlett Publishers.
Connes, P. Hue, O., and Perrey, S. (2010). Exercise Physiology: From a Cellular to an
Integrative Approach. OS Press.
Kraemer, W. J., Fleck, S. J., Deschenes, M. R. (2011). Exercise Physiology: Integrating
Theory and Application. Lippincott Williams & Wilkins.
MacLaren, D., and Morton, J. (2011). Biochemistry for Sport and Exercise Metabolism. John
Wiley & Sons.
Plowman, S. A., and Smith, D. L. (2013). Exercise Physiology for Health Fitness and
Performance. Lippincott Williams & Wilkins.
Porcari, J., Bryant, C., and Comana, F. (2015). Exercise Physiology. F.A. Davis.
Richter, E. A., Kiens, B., Galbo, H., and Saltin, B. (2013). Skeletal Muscle Metabolism in
Exercise and Diabetes. Springer Science & Business Media.
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