Midterm 1 Flashcards
1
Q
What is the air we breathe composed off?
A
20.93% O2, 0.03% CO2 and 79.04% of N2
2
Q
How to calculate VO2 consumed?
A
ViO2- VeO2
Vi= Volume of inspired air, Ve= Volume of expired air
3
Q
formula for calculating VCO2 produced?
A
VECO2 - VICO2
Vi= Volume of inspired air, Ve= Volume of expired air
4
Q
What is the respiratory quotient?
A
the ratio of metabolic gas exchange within the cell
the ratio of CO2 to O2 (CO2 / O2)
5
Q
what is the RQ for protein?
A
0.82
under normal physiological condition, the body does not burn protein for energy
6
Q
What is RER?
A
the ratio of the volume of CO2 expired (VCO2) to O2 consumed (VO2) that we measure during open circuit spirometrey when food is meatbolized for energy production
VCO2/VO2 = RER
7
Q
Why can RER exceed 1.O during high-intensity exercise
A
because of the bicarbonate buffering of anaerobicaly produced H+ accumulating in the blood that leads to extra CO2 production
8
Q
Why does RER drop rapidly after exercise?
A
because of the drop in VE (hypoventilation) and re-establishing blood bicarbonate eq
9
Q
What factors influences RER?
A
- hyperventilation (increase VCO2)
- Diet
10
Q
1 Kcal = how many kj?
A
4.186 kj
11
Q
What is bioenergetics?
A
the study of energy transformations in the human body.
12
Q
Define energy
A
Energy is the capacity to perform work. In exercise physiology, the main forms of energy are chemical, mechanical, and heat energy
13
Q
Define thermodynamics
A
the study of the relationship between heat energy and other forms of energy, such as mechanical energy
14
Q
Why is BMR higher in younger individuals?
A
because they are still growing
15
Q
How is RMR influenced by exercise?
A
- RMR is higher when actively training (HITT) and lifitng
- RMR decreases after training
16
Q
how does training affect exercise efficiency and economy?
A
Greater fitness levels improves energy cycling, greater fat utilization leading to more efficient work
17
Q
How does endurance training affect glycogen
A
it spares glycogen resluting in more fats being metabolized at any submaximal intensity of exercise
18
Q
What is recovery?
A
the sum total of the energetic process that return an individual to or towards a resting state
19
Q
What is the O2 deficit?
A
the period of time at the start of exercise where aerobic metabolism adjust to meet metabolic demands
20
Q
What is exercise and recovery O2?
A
O2 requirement needed for exercise and the O2 needed for recovery from exercise respectively
21
Q
How long does it take for ATP/PCr stores to be restored?
A
- 21-22 seconds, 50% restored
- In 30 seconds, 70% are restored
- 3-5 minutes 100% restored
22
Q
Where does the energy come from to restore ATP/PCr?
A
aerobic metabolism to re-phosphorylate ADP and CR to ATP and PCr
23
Q
Which is the best way to recovery from anaerobic exercise?
A
Active recovery because it keeps the cardiac output elevated
24
Q
What is the second law of thermodynamics
A
when energy is transformed, some energy disperses into a less organized form, increasing the entropy (randomness or disorder) of the system
25
What is ATP?
ATP (adenosine triphosphate) is the source of energy for use and storage at the cellular level
26
Why is ATP the only source of energy muscles can use for contraction?
The enzyme that breaks down ATP, adenosine triphosphatase (ATPase), is structurally bound to the head of the myosin molecule in muscle.
27
Define exergonic and endergonic reactions.
* Exergonic reactions release energy. For example, the breakdown of ATP is an exergonic, catabolic reaction.
* Endergonic reactions absorb energy. For example, building muscle (protein synthesis) is an endergonic, anabolic reaction.
28
What is direct calorimetry?
Direct calorimetry is the measurement of heat energy production.
| One calorie is the amount of heat required to raise the temperature of 1
29
What is indirect calorimetry?
Indirect calorimetry is a method for determining energy expenditure by measuring oxygen consumption (VO2)
| the amount of heat is proportional to the volume of oxygen consumed
30
How much energy is expended per liter of oxygen consumed
~5.0 kcals or ~21 kilojoules of energy
31
What is the difference between RQ and RER?
* RQ reflects the gas exchange ratio at the cellular level.
* RER reflects the gas exchange ratio measured at the lungs.
32
What are the RQ values for carbohydrate, fat, and protein?
- Carbohydrate (CHO): 1.0
- Fat: 0.70
- Protein: 0.82 (not often used in exercise physiology
33
Approximately how much ATP is stored in the body, and how long can this supply last during exercise?
Total body ATP is around 80g, with 4-6mmol/kg stored in muscle. This limited supply can only fuel about 1-2 seconds of exercise.
34
How is ATP replenished during muscle activity?
Through a reversible reaction where chemical energy from other sources is used to re-phosphorylate ADP with Pi (inorganic phosphate), forming ATP
35
What are the four energy sources for ATP resynthesis during muscular work?
1.Breakdown of phosphocreatine (PC or PCr) or creatine phosphate (CP)
2.Adenylate kinase (myokinase) reaction
3.Guanosine triphosphate reaction
4.Food
36
What is the consequence of not having efficient ATP synthesis pathways?
We would require an extra 50-80 kg of ATP per day and an additional 80 kg to run a marathon!
37
Name the three energy systems for ATP production
1.Immediate energy system: ATP-PCr
2.Short-term energy system: Anaerobic glycolysis
3.Long-term energy system: Aerobic system
38
Describe the characteristics of the ATP-PCr system.
fast rate of energy production but low capacity, meaning it can deliver energy quickly but only for a short duration
39
What enzymes are involved in the ATP-PCr system, and what are their functions?
* ATPase: catalyzes the breakdown of ATP
* Creatine kinase (CKase or CK): catalyzes the breakdown of PCr
40
Explain the role of the adenylate kinase reaction in the immediate energy system.
This reaction utilizes the energy stored in an ADP molecule to combine two ADP molecules, producing one ATP and one AMP (adenosine monophosphate), providing a few extra seconds of energy
41
For what type of exercise is the immediate energy system the primary source?
High-intensity, short-duration activities like strength training, powerlifting, and sprinting
42
What are the chronic training adaptations to the ATP-PC system?
Training can increase the activity of ATPase, AK, and CK enzymes, boosting the system's rate and power. Additionally, training can increase PCr stores and slightly increase ATP stores, improving the system's capacity.
43
Explain the concept behind creatine monohydrate supplementation.
Ingesting creatine increases muscle creatine (Cr) stores, which in turn leads to increased phosphocreatine (PCr) storage. This enhances the capacity of the ATP-PCr system.
44
What are the potential performance benefits of creatine loading?
* Enhanced single-bout sprint or strength performance (e.g., 100m sprint, 1RM lift)
* Improved ability to repeat sprint or strength performance (e.g., interval training)
* Potentially increased muscle size (hypertrophy) through indirect mechanisms
45
Describe the standard protocol for creatine loading
20-30 g/day or 0.30 g/kg body mass/day for 3-5 days to rapidly increase muscle Cr and PCr stores
46
Describe the standard protocol for creatine maintenance.
Lower dose (2-5 g/day or 0.03 g/kg/day) for several weeks to sustain elevated levels
47
Which individuals might experience less benefit from creatine supplementation?
Those with high protein intake, naturally high Cr and PCr stores, and a lower percentage of fast-twitch muscle fibers may show less response. Vegetarians may experience a greater response.
48
What are the three classifications of carbohydrates?
.
1. Monosaccharides (basic unit)
2.Oligosaccharides (2-10 monosaccharides)
3.Polysaccharides (3 to thousands of monosaccharides)
49
What are the roles of carbohydrates in the body?
1. Energy source during intense exercise
2. Protein sparer
3. Metabolic primer for fat oxidation
4. Fuel for the central nervous system
50
Where does the energy for intense exercise come from?
Breakdown of blood-borne glucose and muscle glycogen
51
How does carbohydrate intake help preserve tissue protein?
provides an alternative energy source; carbohydrates reduce the body's need to break down protein for fuel, thus sparing protein for tissue building and repair.
52
What is glycogen?
The storage form of carbohydrates in muscle and liver
| the body can store about 2000 kcal of CHO
53
Why is muscle glycogen important during physical activity?
It serves as the major carbohydrate supply for active muscles because it's stored directly within the muscle tissue.
54
How does a carbohydrate-deficient diet impact athletic performance?
It depletes muscle and liver glycogen, negatively affecting performance in short-term anaerobic activity and prolonged intense aerobic activities.
55
How does a high-fat, low-carbohydrate diet affect muscle glycogen?
It leads to less muscle glycogen storage.
56
How does muscle glycogen affect endurance performance?
High muscle glycogen levels sustain exercise for prolonged activity, while depletion leads to performance decline.
57
How does intense short-duration exercise affect liver glycogen?
1 hour of exercise decreases liver glycogen by 55%, and 2 hours almost depletes both liver and muscle glycogen.
58
What is the primary energy substrate during low-intensity exercise?
Fats
59
How do exercise intensity and duration affect fuel mixture?
They determine the relative contribution of carbohydrates and fats as energy sources. Higher intensity exercise relies more on carbohydrates.
60
What are the major functions of lipids in the body?
.1. Energy source and reserve
2. Protection of vital organs
3. Thermal insulation
4. Vitamin carrier and hunger suppressor
61
Why are lipids an efficient energy source?
They carry large quantities of energy per unit weight, transport and store easily, and provide an available energy resource.
62
What is the predominant energy source during light- to moderate-intensity exercise?
fatty acids
63
What are the primary energy sources during moderate-intensity exercise?
Energy is derived from equal amounts of carbohydrates and lipids.
64
What is IMTG?
Intramuscular triacylglycerol, a readily available fat source within muscle tissue.
65
What roles do proteins play in the body?
They contribute to tissue structures and are important constituents of metabolic, transport, and hormonal systems.
66
How does carbohydrate depletion affect protein utilization?
It increases the use of protein as a fuel source.
67
What are BCAAs, and how are they relevant to exercise?
Branched-chain amino acids may serve as a fuel source during exercise.
68
What are the protein requirements for athletes who train intensely?
They should consume between 1.2 and 1.8g of protein per kg of body mass daily.
69
What are the two major functions of anaerobic glycolysis/glycogenolysis?
Generation of ATP and synthesis of pyruvate
70
What is the distinction between glycolysis and glycogenolysis?
Glycolysis is the breakdown of glucose, while glycogenolysis is the breakdown of glycogen.
71
How does the power and capacity of anaerobic glycolysis compare to the ATP-PCr system?
It has lower peak power but greater capacity.
72
When does peak power occur in anaerobic glycolysis?
Around 15-30 seconds
73
What is the capacity of anaerobic glycolysis?
~ 45-90 seconds, or less than 2 minutes.
74
Why is the term “anaerobic” considered a misnomer in metabolism?
Because glycolysis can occur in the presence of oxygen; oxygen is not a reactant in any of the reactions.
75
Where does glycolysis/glycogenolysis take place?
In the sarcoplasm of the cell
76
How is ATP utilized and generated in glycolysis/glycogenolysis?
ATP is used in the initial phases – 2 ATP are required for the endergonic “activating steps” involving phosphate group transfer. Energy is captured in later exergonic reactions, forming 4 ATP from glucose breakdown.
77
What is the net ATP yield from glucose breakdown in glycolysis?
2 ATP
78
79
How many ATP are used when glycogen is the substrate in glycogenolysis?
only 1 ATP
80
What factors can limit substrate availability for glycolysis/glycogenolysis?
Low glucose/glycogen levels due to fasting, disease, improper nutrition, or prior exercise can affect the rate of these pathways
81
What are the three stages of glycolysis?
1. Activation/Priming Stage (Reactions 1-3)
2. Splitting Stage (Reactions 4 & 5)
3. Oxidation/Reduction Stage (Reactions 6-10)
82
What happens in the first activation step of glycolysis?
An endergonic reaction (splitting one ATP) increases the potential energy of the product. This reaction, catalyzed by hexokinase, is inhibited by glucose-6-phosphate (feedback/product inhibition). The phosphorylation of glucose traps it in the cell, committing it to either glycolysis or glycogenesis.
83
Is the first activation step of glycolysis required when glycogen is the substrate?
No, and this saves one ATP.
84
What is the function of glycogen phosphorylase?
to initiate the breakdown of glycogen.
| glycogen phosphorylase is an enzyme
85
What activates glycogen phosphorylase?
Pi, Ca2+, and cAMP (via epinephrine/norepinephrine)
86
What happens in the second activation step of glycolysis?
Another endergonic reaction (splitting one ATP) increases the product's potential energy. This step is catalyzed by phosphofructokinase (PFK), a major rate-limiting enzyme of glycolysis.
87
What factors inhibit PFK activity?
ATP, PCr, citrate, and increased H+ (decreased pH)
88
What factors activate PFK activity?
ADP, Pi, and AMP
89
What happens during the splitting stage of glycolysis?
wo reactions split the six-carbon fructose 1,6-bisphosphate into two three-carbon phosphoglyceraldehyde molecules for use in the next stage
90
What occurs during the oxidation/reduction stage of glycolysis?
Reactions increase the potential energy of the product and reduce NAD+ to NADH + H+, which can be used to reduce pyruvate to lactate or be shuttled to the mitochondria for ATP generation in the electron transport chain.
| reduction is when a molecule gains an electron
91
Why is the ratio of NAD+ to NADH + H+ important for glycolysis?
The rate of stage 3 depends on NAD+ availability.
92
What are the products of the oxidation/reduction stage of glycolysis?
The first reaction generates 2 ATP, and the second reaction generates another 2 ATP and 2 pyruvate molecules.
93
What is the overall outcome of the glycolysis pathway?
- Converts Glucose-6-phosphate (6C) into 2 Pyruvate (2 x 3C)
- Consumes 2 ATP
- Forms 2 NADH + H+
- Generates 4 ATP
- Net gain: 2 ATP and 2 NADH + H+
94
What are the two possible pathways of pyruvate?
1. Entry into mitochondria for oxidation
2. Reduction to lactate
95
What enzyme catalyzes the reduction of pyruvate to lactate?
Lactate dehydrogenase (LDH)
96
What happens to NADH + H+ and NAD+ during the reduction of pyruvate to lactate?
NADH + H+ is converted to NAD+, which is required to keep glycolysis going.
97
key features of the short-term energy system (anaerobic glycolysis)?
- Relies on glucose from blood and glycogen from muscle
- Provides moderately high rates of energy expenditure (e.g., 200-meter sprint)
- Power: 15-30 seconds (less than 30 seconds)
- Relatively low capacity for high-intensity work (e.g., 1 km cycling, approximately 60 seconds)
- Capacity: 45-90 seconds (less than 2 minutes)
98
What are the training adaptations to the short-term energy system?
1. Increased activity of key glycolytic enzymes (PFK, hexokinase, phosphorylase, and LDH), increasing the power of the system
2. Increased skeletal muscle buffering capacity (resistance to pH changes), increasing the capacity of the system
3. Increased glycogen stores within muscle, increasing the capacity of the system and also important for power
99
What does the wingate test for?
it asses the short-term energy system. It measures peak and mean power ouput during a 30-second maxiaml effort on an ergometer
100
Which energy system is the only one that can break down all three macronutrients?
The aerobic system
101
What are the biochemical pathways involved in the aerobic system?
The biochemical pathways involved in the aerobic system completely break down glucose/glycogen, fats, and some amino acids to produce a large amount of energy (ATP). This process also releases CO2 and H2O
102
What happens to pyruvate during aerobic exercise?
During aerobic exercise, the pyruvate produced from glycolysis enters the mitochondria via the monocarboxylase transporter 1 (MCT1) protein channel.
103
How does NADH+H+ from glycolysis enter the mitochondria?
- the malate-aspartate shuttle (primarily used by the heart and slow-twitch skeletal muscle)
- The glycerol phosphate shuttle (primarily used by fast-twitch muscle)
104
How many ATP are produced during "aerobic" glycolysis?
6-10 ATP
105
What are the important products of "aerobic" glycolysis?
Pyruvate and NADH+H+ are the important products. They are used in the mitochondria.
106
What happens to pyruvate once it's inside the mitochondria?
Pyruvate is converted to acetyl CoA, which then enters the Krebs cycle.
107
What enzyme converts pyruvate to acetyl CoA?
Pyruvate dehydrogenase (PDH) is the enzyme that converts pyruvate to acetyl CoA. This process:
- Loses 1 carbon atom in the form of CO2.
- Produces 1 NADH+H+ molecule.
108
Where do the reactions of the Krebs cycle take place?
The Krebs cycle reactions occur inside the mitochondrial matrix.
109
Where are mitochondria located within a muscle fiber?
1. Intermyofibrillar (IM): primarily supplies ATP for the contractile apparatus (myofibrillar ATPase, SR-ATPase).
2. Subsarcolemmal (SS): primarily supplies ATP for membrane transport (Na+-K+ ATPase), O2 extraction, and phosphorylation of glucose.
110
What are the main products of the Krebs cycle?
- NADH+H+
- FADH2
- ATP (from the phosphorylation of ADP in the "guanosine triphosphate (GTP) reaction")
111
What are the byproducts of the Krebs cycle?
- CO2
- H2O
112
How many NADH, FADH2, ATP, and CO2 molecules are produced from one turn of the Krebs cycle?
One turn of the Krebs cycle produces:
- 3 NADH
- 1 FADH2
- 1 ATP
- 2 CO2.
113
Where are the protein complexes involved in the electron transport chain (ETC) located?
The protein complexes of the ETC are located in the inner mitochondrial membrane
114
Describe the flow of electrons in the ETC.
Electrons from NADH+H+ and FADH2 are transferred through protein complexes in the inner mitochondrial membrane:
- NADH+H+ - Complex I - Coenzyme Q - Complex III - Cytochrome c - Complex IV
- FADH2 - Complex II - Coenzyme Q - Complex III - Cytochrome c - Complex IV
115
What happens to the electrons and H+ at the final cytochrome oxidase complex (Complex IV)?
They combine with oxygen to form water
116
How is ATP generated in the ETC?
○ H+ from NADH+H+ and FADH2 are pumped through the protein complexes and accumulate in the inter-membrane space.
○ This creates a concentration gradient.
○ H+ flows back to the matrix through ATP synthase (Complex V), activating the enzyme to phosphorylate ADP + Pi to ATP.
117
Why does FADH2 yield fewer ATP than NADH+H+?
FADH2 enters the ETC at Complex II, which does not pump H+ across the membrane. This results in fewer H+ being pumped for FADH2, leading to less ATP production.
118
What is the rate-limiting step in the ETC?
cytochrome oxidase step (Complex IV)
119
What is the total energy yield from one glucose molecule in aerobic metabolism?
30-32 ATP
120
What happens to fatty acids once they enter the muscle cell?
1. They are "activated" using ATP to produce fatty acyl-CoA.
2. Fatty acyl-CoA is transported into the mitochondria via the carnitine shuttle OR converted and stored as triglyceride in the muscle.
121
122
What happens in the beta-oxidation cycle?
Beta-oxidation is a four-step process that removes acetyl CoA units one at a time from a fatty acyl CoA molecule. Each cycle produces:
- NADH+H+
- FADH2
- Acetyl CoA (which enters the Krebs cycle)
123
What is the rate-limiting enzyme for beta-oxidation?
B-ketothiolase
124
How many ATP are produced from the metabolism of one 18-carbon fatty acid (stearic acid)?
~120 ATP
125
What is the total ATP yield from one triglyceride molecule?
~ 379 ATP. This includes ATP from the three fatty acids (3 x 120) and glycerol metabolism (~19 ATP)
126
Do fats require carbohydrates to be fully metabolized?
Yes. Pyruvate (generated from carbohydrates via glycolysis) is needed to produce oxaloacetate, which is the "initiating step" for the Krebs cycle. Oxaloacetate combines with acetyl CoA (from fat metabolism) to form citrate and start the cycle. Without sufficient carbohydrates, fat metabolism slows down because acetyl CoA cannot enter the Krebs cycle efficiently.
127
What is the pyruvate carboxylase reaction?
a reaction converts pyruvate to oxaloacetate. It requires ATP.
128
What percentage of total energy requirements for an endurance event can come from amino acids?
~ 5-10%
129
How are amino acids used for energy?
Amino acids can be converted to pyruvate, acetyl-CoA, or enter the Krebs cycle as intermediaries after the removal of an amino group (-NH2) through deamination or transamination
130
What are the factors that control the aerobic system?
1. Complexity of pathways:
■ Transportation problems across membranes
■ Substrate availability (e.g., fat in adipose tissue is not in close proximity to muscle)
2. Rate-limiting steps:
■ Krebs cycle: isocitrate dehydrogenase
■ Beta-oxidation: B-ketothiolase
■ ETC: cytochrome oxidase
■ Glycolysis: PFK
3. Substrates:
■ CHO (muscle glycogen or blood glucose) can be a limiting substrate, leading to fatigue ("hitting the wall")
■ Fats may rely on some CHO for complete oxidation
■ Intensity and duration of exercise are key components for determining substrate utilization
131
How do intensity and duration of exercise influence energy system contribution?
* The power and capacity of energy supply depend on the intensity and duration of exercise.
* This determines which energy system predominates in a given activity.
132
True or False: The terms "lactate" and "lactic acid" are interchangeable.
false
133
What happens during the conversion of pyruvate to lactate?
In the presence of NADH+H+ and lactate dehydrogenase (LDH), pyruvate is converted to lactate. This process:
- Consumes H+ ions.
- Releases NAD+
134
135
Is lactic acid the cause of muscle acidosis?
No. Lactic acid never really exists. Lactate is a consequence of anaerobic glycolysis and a consumer of muscle acidosis
136
What are the possible fates of lactate generated during glycolysis?
○ Oxidation in the muscle where it was produced.
○ Accumulation in the muscle.
○ Efflux to other muscle fibers.
○ Efflux to the blood.
○ Oxidation by other tissues (e.g., heart, brain).
○ excretion in sweat and urine.
○ Conversion into glucose in the liver (Cori cycle)
137
What is the lactate shuttle?
The lactate shuttle refers to the formation of lactate in one cell compartment and its use in another (within the same muscle or between muscle fibers/organs). Lactate can act as a fuel source
138
Why do we measure blood lactate during exercise?
Blood lactate coincides with increased glycolytic activity and acidification of muscle and blood. It can be used to:
○ Assess individuals' fitness.
○ Monitor training program effectiveness.
139
Does high-intensity anaerobic exercise increase or decrease muscle pH?
High-intensity anaerobic exercise decreases muscle pH (increases H+ concentration), despite the controversy surrounding lactate and lactic acid.
140
What are the primary sources of H+ ions during high-intensity anaerobic exercise?
Two primary sources:
1. Net production (release) of H+ from intermediary compounds in glycolysis.
2. H+ release during ATP hydrolysis.
■ There are likely a few other sources as well.
141
List some physiological effects of H+ ions generated during high-intensity exercise.
○ Decreased ATPase activity.
○ Inhibition of Ca2+ binding at troponin.
○ Decreased skeletal muscle metabolic enzyme activity (e.g., PFK).
○ Interference with Ca2+ regulation.
○ Stimulation of nociceptors, causing pain sensation.
142
What is one of the most important physiological mechanisms to resist changes in muscle pH?
Buffering capacity. This is the ability to resist changes in pH.
143
How does high-intensity anaerobic training affect anaerobic power, muscle pH, and buffering capacity?
Training increases anaerobic power, increases muscle pH before exercise, and increases buffering capacity.
| sprinters and rowers have the highest buffering capacity
144
Which types of athletes have the highest buffering capacity and anaerobic ability?
Athletes who hold their breath while performing, such as swimmers, have the highest buffering capacity and anaerobic ability.
145
How does buffering capacity help maintain anaerobic power?
Buffering capacity helps maintain pH in muscle, extending anaerobic power production, and reducing power drop-off.
| buffering H+ ions delays the onset of fatigue associated with acidosis.
146
How is bicarbonate loading performed?
- ingest 0.3 g/kg body mass of sodium bicarbonate 1-3 hours before exercise, along with 500 ml to 1 liter of water.
- load over 5-6 days with 0.125 g/kg (plus 250 ml water) four times per day, ending 4 hours prior to the event
147
What is the effect of bicarbonate loading on blood and muscle pH?
Bicarbonate loading increases blood HCO3- concentration and blood pH, but not resting muscle pH.
148
What is an alternative to sodium bicarbonate for buffering H+ ions?
Sodium citrate is an alternative to sodium bicarbonate with fewer side effects
149
What is beta-alanine, and how does it relate to buffering capacity?
- Beta-alanine is a non-essential amino acid that is a precursor to carnosine production in skeletal muscle
- Carnosine is a potent buffer of H+ ions and may stimulate nitric oxide, which is a vasodilator. Carnosine also has antioxidant properties.
150
What is a typical dosing protocol for beta-alanine?
~6 g/day for 1-2 weeks, then reduce to 3-4 g/day for 4-12 weeks, and then cycle off.
151
Define fatigue
Fatigue is the inability to maintain a desired power output or force during any type of repeated or sustained muscle contraction.
152
What are the causes of fatigue?
* Type of exercise
* Intensity
* Duration
* Energy systems utilized
* Physiological consequences of the exercise bout.
153
Some factors involved in fatigue.
○ ATP-PC depletion.
○ Metabolite accumulation/ionic imbalance (H+, Ca2+, Na+/K+, NH4+/NH3, Pi).
○ Glycogen depletion.
○ Oxygen supply.
○ Central and peripheral neural factors.
154
How does "ATP-PC" depletion contribute to fatigue.
"ATP-PC" depletion results from a decline in ATP and PC stores during exercise.
○ PC can deplete to about 15% of resting values.
○ ATP rarely depletes below 40% of rest before short-term muscular fatigue occurs.
○ This is a primary concern for activities like sprinting, strength exercise, and high-intensity interval training
155
How does glycogen depletion contribute to fatigue?
Depletion of muscle glycogen reduces the rate and capacity of glycolysis/glycogenolysis. This leads to:
○ Reduced production of pyruvate
○ Decreased blood glucose, which can impair central nervous system function and lead to loss of coordination
○ Pi accumulation interferes with Ca2+ release at the sarcoplasmic reticulum (SR) and Ca2+ binding at troponin, resulting in a decrease in muscle force at the cross-bridge site.
156
How does oxygen delivery contribute to fatigue?
Desaturation of hemoglobin with oxygen during high-intensity aerobic exercise can decrease the rate of aerobic metabolism.
| reliance on glycolytic energy meatbolism & fatigue-related byproducts
157
Explain how neural factors contribute to fatigue.
1. Peripheral fatigue involves impaired regulation of acetylcholine at the motor end plate (neuromuscular junction), reducing muscle membrane excitability.
2. Central fatigue which involves loss of motivation, drive, and concentration, Pain intolerance, & Increased serotonin levels in the brain, which can induce fatigue during prolonged endurance exercise
| Serotonin increases lethargy, sleepiness and negative mood states.
## Footnote
Serotonin supresses dopamine
