exercise science unit 2 Flashcards
1
Q
Homeostasis
A
maintenance of a relatively constant internal environment during resting conditions
“dynamic constancy” with minimal fluctuation around a set point
2
Q
stead state
A
a physiological variable remains stable but not necessarily at resting values
3
Q
mechanical control systems
A
change away from set point triggers heating/cooling
return to set point turns off heating/cooling
ex. thermostat set to a specific temperature (or baroreceptors in blood vessels)
4
Q
A
5
Q
biological control system
A
main control system
3 components work to maintain a variable near set point
- sensor/receptor: activated by a change in variable
- control center: receives information from sensor; sends information to effector
effector: brings about appropriate response
6
Q
negative feedback
A
most common type of control to maintain homeostasis
response of the control system is opposite stimulus
7
Q
positive feedback
A
response of the control system increases the original stimulus
8
Q
gain
A
gain reflects the capability (precision) of a control system to maintain homeostasis
gain = (correction)/(error)
large gain means a system can achieve a large magnitude of correction with limited error
9
Q
how does exercise change homeostasis?
A
skeletal muscle produces excess heat during heavy exercise
more oxygen is required and more CO2 produced during exercise
during intense or prolonged exercise, the body cannot maintain true homeostasis
severe disturbance in homeostasis lead to fatigue, then cessation of exercise
10
Q
How does exercise improve homeostatic control?
A
cellular adaptation: change in cell structure or function
adaptations improve the cell’s ability to maintain homeostasis
prolonged exposure to stressor can make cells more responsive to that particular stress
- exercise
- environment (acclimation)
11
Q
exercise-induced hormesis (how body adapts to stress)
A
stressors have the capability to cause harm or cause beneficial effects
too little stress: negative effects (immobilization, astronauts)
too much stress: injury or dysfunction (overuse injuries, stress fractures
optimal dose, intensity, duration of stress: positive adaptation
exercise stressors: thermal, metabolic, mechanical
exercise triggers adaptation through cell signaling pathways
12
Q
intracrine signaling
A
chemical messenger produced inside one cell triggers pathways in the same cell
13
Q
juxtracrine signaling
A
cytoplasm in two adjacent cells is connected via a small junction
signals can be transmitted to other local cells through junction points
14
Q
autocrine signaling
A
cell releases a chemical messenger into extracellular fluid
messenger then acts on the same cell producing the signal
15
Q
Paracrine signaling
A
cell produces a chemical messenger to act locally on nearby cells
16
Q
endocrine signaling
A
tissue release chemical messengers (hormones) that are transported throughout the body
messengers act only on cells that have specific hormone receptor
17
Q
stress proteins
A
normal function: proteins have important roles as enzymes, intracellular transporters
stressors can cause damage to cells and disturbance to homeostasis
cellular stress response: biological control system triggers cells to rapidly make specific proteins to defend against stress
1 type of stress protein is heat shock proteins
exercise training results in significant production of heat shock proteins in heart, skeletal muscle
18
Q
protein synthesis process in muscle tissue
A
- stress (exercise) in myocyte triggers cell signaling pathways
- transcriptional activators responsible for turning on specific genes to make new proteins move into the cell nucleus
- transcriptional activators bind to gene promoters and stimulate transcription
- DNA transcribed to messenger RNA (mRNA)
- mRNA leaves cell nucleus and travels to ribosome
- mRNA is translated into a specific protein
19
Q
adaptations from exercise
A
exercise promotes cellular adaptation: there are some common genes activated, regardless of the type of activity
different modes of exercise promote different gene expression in muscle fibers
endurance training vs resistance training vs plyometric training will cause different adaptations
20
Q
Acids
A
molecule that can liberate hydrogen ions H+
increase the H+ concentration in a solution (lower pH)
lactic acid is a strong acid
21
Q
Base
A
molecule capable of combining with H+
Decreases H+ concentration in a solution (incr. pH)
bicarbonate (HCO3-) is a strong base
22
Q
normal pH
A
7.4
23
Q
Alkalosis is another word for…
A
base
24
Q
What is metabolic acidosis?
A
gain in the amount of acid in the body
high intensity exercise (abolve lactate threeshold) lasting >30s
25
what is a condition and disease that promotes metabolic acidosis?
long-term starvation: results in increased fat metabolism and elevated production of ketoacids
uncontrolled diabetes: results in high rates of fat metabolism and diabetic ketoacidosis
26
conditions and diseases that promote metabolic alkalosis
loss of acids from the body
severe vomiting
kidney disease
27
how does the body produce hydrogens during exercise?
production of carbon dioxide: end-product of oxidative phosphorylation
production of lactic acid: glucose metabolism via glycolysis
ATP breakdown during muscle contraction: results in release of H+
28
what is the importance of acid-base balance
increased H+ impairs performance: may inhibit key enzymes associated with metabolism (glycolytic or TCA activity)
H+ competes with Ca2+ binding sites on troponin and can impair muscle contraction
29
what are some acid-base buffer systems?
intracellular buffer: proteins, phosphate groups, bicarbonate
extracellular buffer: bicarbonate, hemoglobin, blood proteins
respiratory influence: quick
kidneys: slow, non-exercise effect
30
bicarbonate buffer
converts strong acid into weak acid
HCO is most important extracellular buffer
31
phosphates buffer
converts strong acid into weak acid
32
protein buffers
acepts hydrogens
33
histidine-dipeptides or carnosine buffer
accepts hydrogens
34
sodium-hydrogen exchanger as buffer
takes sodium into the cell and hydrogen out
35
monocarboxylate transporter as buffer
takes hydrogen and lactate out of the cell
36
muscles protect against pH by...
intracellular buffers and H+ ion transporters
37
How is muscle buffering capacity fiber-type specific
intracellular buffering capacity is greater in type 2 fibers compared to type 1
this adaptation is advantageous in performances that rely on fast type fiber recruitment
- also benefitted by upregulation of carnosine and H+ transporters
38
what are three principes of the extracellular buffer system
proteins, hemoglobin, bicarbonate
39
additional information about bicarbonate buffering system in extracellular buffers
hb has 6X the capacity of other proteins
deoxygenated Hb > oxygenated Hb
40
respiratory influence
involved with carbonic acid dissociation
when pH dereases, H+ increases
reaction shifts to the left
CO2 is "removed" by the lungs and pH increases
41
kidney buffer influence
important role w/ long-term acid-base balance
- slow process serves minor role with exercise
kidney contributes to acid-base balance (at rest) by regulating bicarbonate concentration in blood
- when blood pH decreases, bicarbonate excretion is reduced
- when blood pH increases, bicarbonate excretion is increased
42
H+ production during exercise for acid-base balance
exercise intensity
amount of muscle mass involved: more type 2
duration of exercise
43
blood pH during exercise for acid-base balance
declines with increasing intensity of exercise
43
How are H+'s buffered during exercise in the muscle (1st line of defense)?
60% intracellular proteins
20-30% muscle bicarbonate
10-20% intracellular phosphate groups
43
muscle pH during exercise for acid-base balance
declines with increasing intensity of exercise - muscle pH is lower than blood pH
- muscle is site of H+ production and has lwoer buffering capacity
44
How are H+'s buffered during exercise in the blood?
bicarbonate is major buffer
hemoglobin and blood proteins play minor role
45
the central nervous system consists of
the brain and spinal cord
46
the peripheral nervous system consists of
nerves and ganglia outside the CNS
affect fibers transmit impulses from body receptors to CNS
efferent fibers transmit impulses from CNS to body effector organs
47
Sensory (afferent) functional divisions
somatic: input is consciously perceived
visceral: input is not consciously perceived
48
Motor (efferent) functional divisions
somatic: control of skeletal muscle
autonomic: involuntary control of smooth muscle in blood musessels, cardiac muscle, endocrine glands
49
what are the parts of the neuron?
cell body (1): contains the cell nucleus
dendrites (multiple): function as neuron's receivers, carry impulses towards the cell body
Axon (1): carries electrical impulses called action potentials away from the cell body
50
what do schwann cells do in axons?
form an insulating layer on large nerve fibers
cell membranes produce a substance called myelin
PNS
51
saltatory conduction
myelin makes a non-continuous sheath separated by nodes of Ranvier
depolarization happens more quickly because impulses can skip from node to node along myelinated fibers
52
nerve conduction
neurons are excitable cells with specific properties:
- irritability: ability to respond to a stimulus and trigger a neural impulse
- conductivity: ability to transmit impulse long the axon
electrical impulses transmit information and are referred to as action potentials
process involves change in the electrical charge difference across the cell membrane
53
what is the resting membrane potential inside a cell>
difference in electrical charge between the inside and outside of a cell
causes: uneven separation of charges between the inside and outside of a cell
causes:
- uneven separation of changed anions (-) and cations (+)
- selectively permeable cell membrane
typical resting potential for a neuron: -70 mV
- inside is more negative than outside
54
how is resting membrane potential maintained?
higher concentration of sodium outside cell
- channels that allow movement of sodium across membrane are closed at rest and do not allow Na in
higher concentration of K inside cell
- leak channels are open and allow slow movement of K out of cell
sodium/potassium pumps use ATP to maintain concentration gradients
- Pumpkin: pump 2 K in, 3 Na out
55
what happens during depolarization?
stimulus changes permeability of membrane: Na+ channels open
sodium flows into the cell from area of high to low concentration
inside of cell becomes less negative
- membrane potential charges -70 mV -> 0 mV
if a specific threshold value is reached (-55 mV), voltage-gated sodium gates open and an action potential is triggered
action potential spreads along the axon at the nodes of raviere
legante gated channels open first than voltage after -55 mV voltage is reached
56
what happens during repolarization?
depolarization to +30 mV causes Na+ channels to close and K+ channels to open
potassium flows rapidly out of the cell, from area of high to low concentration
process restores resting membrane potential
hyperpolarization: brief period where membrane potenital is more negative than -70 mV and it is more difficult for a nerve impulse to arise
57
graded potentials
changes in electrical potential can vary in intensity and are known as graded potentials
- these can excite or inhibit a neuron
- graded potentials decrease in signal strength as they move from their point of origin
58
action potential
action potentials are all or none depolarization from the trigger zone proceeding down the length of a neuron axon
- begin as a graded potential but must reach threshold
- only excitatory
59
where do the voltage gated channels live on an axon?
axon hillock
60
initial signal: graded potential
1. stimulus allows movement of sodium through ligand gated channels
2. localized area of the cell depolarized and become more positive
3. if threshold is not reached, sodium potassium pumps restore resting membrane potential
61
continued graded potentials -> threshold
1. additional stimulus and localized depolarization
2. inside of cell reaches threshold value of -55 mV
62
action potential steps
1. when threshold is reached, voltage-gated channels at axon hillock allow rapid sodium entry
2. charge inside cell becomes positive
3. all-or-none depolarization = action potential
63
synapse definition
region where axon terminal of neuron communicates with rarget cell
64
synapse parts
presynaptic: neuron sending the signal
synaptic cleft: gap at the communication point between the two cells
postsynaptic: neuron or other cell receiving the signal
65
neurotransmitter definition
chemical messenger released from presynaptic membrane
66
neurotransmitter steps
moves across synaptic cleft to bind to receptors on postsynaptic membrane
signal changes from electrical -> chemical -> electrical
67
excitatory postsynaptic potentials
promote depolarization
membrane potential becomes less negative and can lead to action potential
68
inhibitory postsynaptic potential
cause hyperpolarization
membrane potential becomes more negative and makes it more difficult for an action potential to occur
69
temporal summation
sum of several EPSP from one presynaptic neuron starts the action potential
70
spatial summation
sum of EPSP from several different presynaptic neurons starts the action potential
71
clearance of neurotransmitters?
after the neurotransmitter binds to postsynaptic receptors, signal transmission is complete
end result of neurotransmitter:
- degraded by enzymes
- actively transported back into presynaptic terminals
- diffuses away from synapse
72
afferent receptors
joint proprioceptors
muscle proprioceptors
kinestesia
muscle spindle
Golgi tendon organs
muscle chemoreceptors
73
Joint proprioceptors
located in joint capsules
sense joint position & speed of movement
74
muscle proprioceptors
muscle spindles: sensitive to muscle length and rate of change
goldi tendon organs: sensitive to tension in tendon and strength of contraction
75
kinesthesia
conscious recognition of the position of body parts in space as well as recognition of the speed of limb-movement
76
muscle spindle
length detector in muscle
highest denisty in muscles involed in fine motor control
consists of: intrafusal fibers: run parallel to normal muscle fibers & Gamma motor neurons: stimulate intrafusal fibers to contract along with extrafusal fibers
77
How do muscle spindle fibers work?
when muscle spindles sense muscle is stretched:
- sensory neurons conduct action potential to spinal cord
- synapse with alpha motor neurons
- stimulate muscle to contract and shorten
78
golgi tendon organs
sensory nerve fibers woven into tendon (in series with extrafusal fibers)
monitor force development (tension) within muscle
prevent muscle injury due to excessive force
79
80
How do golgi tendon organs work?
when GTO's sense too much tension on a tendon:
- sensory neurons conduct action potential to spinal cord
- synapse with inhibitory interneurons
-interneurons synapse with and inhibit alpha motor neurons
- muscle relaxes and relieves tension on tendon
81
muscle chemoreceptors
sensitive to changes in chemical environment surrounding muscle fibers (H, CO2, K)
provide CNS with information about muscle metabolism in exercise
- important in control of cardiovascular and pulmonary responses to exercise
82
somatic motor control (efferent division)
mtor neurons
- cell bodies within the spinal cord
- axons carry impulses from CNS to muscle
- motor unit: one alpah motor neuron and all muscle fibers it innervates
83
somatic motor control (efferent division) innervation ratio
fine motor control: low ration (23:1)
gross motor control: high ratio (1000:1)
84
cerebral cortex's function in motor control (efferent)
organization of complex movements
storage of learned experiences
reception of sensory information
sums input from several other regions of the brain and sends motor commands to spinal cord
85
cerebellum's function in motor control (efferent)
coordinates and monitors complex movements
adjusts movement in response to proprioceptive feedback
may initiate fast, ballistic movements
86
brainstem's function in motor control (efferent)
control of eye movement
major structures: medulla, pons, midbrain
equilibrium
postural tone
complex reflexes: gag/cough
cardiopulmonary control and metabolic functions
87
basal ganglia's function in motor control (efferent)
selection of correct movement and inhibition of incorrect movement
tremors are from damage to basal ganglia
88
spinal cord's function in motor control (efferent): spinal tuning
neural networks within the spinal cord refine voluntary movement
after receiving initial messages from high brain centers
intrinsic spinal networks : central pattern generators - program/ fine tune movement done often
89
spinal cord's function in motor control (efferent): reflexes
withdrawal and crossed extensor
activation of skeletal muscle in response to sensory input
responses are involuntary and independent of higher brain centers
90
withdrawal and crossed extensor
flex on same side extension on opposite side
91
autonomic nervous system function
control of involuntary internal functions
exercise related autonomic regulation:
-heart rate
- blood pressure
-respiration
91
sympathetic
"Fight or flight"
Stimulation results in:
Increased HR and BP
Increased blood flow to muscles
Increased airway diameter
Increased metabolic rate
Increased cognition
91
parasympathetic
"Rest and digest"
Stimulation results in:
Lowered HR and BP
Bronchoconstriction
Increased blood flow to glands and gut, promoting digestion
Conservation of energy
92
Transmission of autonomic impulses
All pathways consist of 2 neurons
Presynaptic neuron cell body is located in brain or spinal cord
First synapse occurs at a ganglion (cluster of cell bodies outside CNS) or near target tissue
-Neurotransmitter is acetylcholine
Postsynaptic neuron extends to synapse with target cells
-Parasympathetic NT is acetylcholine – target has cholinergic receptors
-Sympathetic NT is norepinephrine – target has adrenergic receptors
93
What are the two pathways in the neuroendocrine system?
nervous system uses NTs to relay messages via nerves
endocrine system releases hormones into blood (via glands)
94
What are the different classifications of hormones?
steroid: lipid soluble
peptide: most non-steroid hormones
amines: thyroid and adrenal medulla hormones
95
What is blood hormone concentration determined by?
rate of secretion of hormone from endocrine gland (magnitude of input (stimulatory or inhibitory))
rate of metabolism or excretion of hormones (may occur near receptor, in liver, or in kidneys
quality of transport proteins (capacity- max quality of hormone bound to protein, Affinity - chemical tendency of a hormone to bind to protein)
Changes in plasma volume (concentration inversely related to plasma volume
96
How do hormones limit the scope of their effect?
Hormone-specific receptors
- concentration of hormone
-affinity of receptors for hormone
- number of receptors on cell
97
downregulation
decrease in receptor number in response to high concentration of hormone
98
99
upregulation
increase in receptor number in response to low concentration of hormone
100
What are the mechanisms of hormones for slow-acting hormones?
activation of genes to alter protein synthesis
101
What are the mechanisms of hormones for fast acting hormones?
activating second messengers vis G protein: links interaction outside cell with subsequent events inside of cell
altering membrane transport
- activate carrier molecules in or near membrane
102
What are the major endocrine glands involved in improving exercise?
hypothalamus, pituitary gland, adrenal gland, pancreas
103
what parts of the body are in control of slow acting hormones?
anterior pituitary gland (GH)
adrenal cortex (cortisol)
104
what parts of the body are in control of fast acting hormones?
adrenal medulla (epinephrine and norepinephrine)
pancreas (insulin and glucagon)
105
why focus on hormones related to substrate mobilization?
need way more energy from exercise: release nutrients into blood stream and meet high demands of exercise
- the demand for carbohydrate energy is HUGE compared to blood glucose content means to sustain blood glucose and some for the working muscles
106
endogenous glucose production
Liver Glycogenolysis
-Converts liver glycogen into glucose
Liver Gluconeogenesis
-Produce ”new” glucose from other compounds
-Ex. Lactate, glycerol, some amino acids
Muscle glycogenolysis
-Convert muscle glycogen into glucose 6-phosphate
Not considered EGP
107
hypothalamus
Serves as sensor system
-Directly detects factors such as osmolarity/temperature
-Receives afferent input from other sensors
Responds with
-Hormone signals
-Neurologic signals
108
hypothalamic and anterior pituitary communication
blood connection
portal system carries releasing hormones directly to anterior pituitary
109
hypothalamic and posterior pituitary communication
neurologic connection
extension of hypothalamus
secretes hormones made in the hypothalamus
110
Growth hormone big picture
exercise is most potent stimulus (sleep, stress, low plasma glucose)
released from anterior pituitary
- stimulated by GHRH, inhibited by somatostatin
promotes muscle growth: stimulates release of IGF-1
influences on metabolism - preserve plasma glucose
111
intensity and duration of exercise effect on GH
magnitude of release depends on exercise intensity
higher duration = higher GH
111
maintenance of plasma glucose
gluconeogenesis in liver and adipose tissue (triglycerides) increases plasma glucoses while tissues (glucose) decreases
112
cortex: adrenal gland
adrenal cortex: outer portion
- secretes cortisol and aldosterone
113
cortisol big picture
responds to various stimuli: exercise, bone break, burns, stress
Hypothalamic-pituitary- adrenal (HPA) axis
Corticotropin-releasing hormone (CRH)
Adrenocorticotrophic hormone (ACTH)
maintenance of plasma glucose
114
cortisol response to acute exercise
in general, high exercise stress is needed to markedly influence cortisol (high intensity and/or duration)
115
diurnal variation in cortisol levels
depends on time of day
increase to 6am once wakes up, drops
116
medulla: adrenal gland
adrenal medulla: inner portion "marrow"
- secretes catecholamines (norepinephrine and epinephrine)
117
function of catecholamines
-Muscle glycogen mobilization (glycogenolysis)
-Mobilization of glucose from liver (glycogenolysis)
-FFA mobilization (lipolysis)
-Interfere with glucose uptake
Also, critically important for
-Heart rate, contractile force, and blood pressure
118
epinephrine vs. Norepinephrine
Most epinephrine (E) in blood comes from adrenal medulla
-80% of adrenal medulla secretion is E
Rise in plasma norepinephrine (NE) originates from sympathetic nerve endings other than in adrenal medulla
-NE acts primarily when released as NT at target tissue
-Diffuses into blood stream from interstitial space (spillover
119
catecholamines response w/ training
decreased plasma levels at fixed workload with endurance training
120
catecholamines response to acute exercise
both epinephrine and norepinephrine increase
121
catecholamines response w/ training
trained individuals have greater response with heavy/very heavy exercise
122
pancreas
Both endocrine and exocrine functions
Hormones released from groups of cells within the endocrine portion called islets of Langerhans
Secretes two counter-regulatory hormones
-Insulin
-Glucagon
123
insulin
Lowers blood glucose
-Secreted by beta-cells (pancreas) when plasma glucose is elevated (occurs postprandially)
Functions:
-Facilitates glucose transport into cells
-Enhances synthesis of glycogen, protein, and fat
-Inhibits gluconeogenesis
Inhibited by epinephrine
You can think of insulin as a ”brake” on processes that mobilize stored fuel
124
Glucagon
Raises blood glucose
-Secreted by alpha-cells (pancreas) when plasma glucose is lower than normal
Functions:
-Promotes liver glycogenolysis & gluconeogenesis
-Increases lipolysis of adipose tissue
Stimulated by epinephrine
125
insulin response to acute exercise
decreases during exercise
- even lower when trained
126
If insulin is important for getting glucose into cells, and insulin decreases during exercise, how does muscle take up blood glucose?
Two explanations:
↑ insulin sensitivity to receptors on muscle
-Less insulin needed for same effect
Contraction-mediated glucose transport
-GLUT4 is the major transporter and must be “moved” from an intracellular location to the plasma membrane
-Contraction activates signaling proteins that facilitate translocation of GLUT4 to assist with glucose intake
127
Glucagon response to acute exercise
increases till about 30 min then levels off
- trained lower level
128
fat and carb burning relation to crossover concept
when intensity increases, carbs increase w/ very little from fat
- H+ lactate provide higher storage of triglycerides and lower hypolysis, reason for low fat for high intensity exercise
129
fluid balance during exercise
During exercise, plasma volume decreases
- increase in hydrostatic pressure, tissue osmotic pressure;
- decrease in plasma water content via sweating (evaporation)
Results in:
- lower blood pressure, heart works harder
Endocrine glands involved with fluid imbalances:
Posterior pituitary gland
Adrenal cortex
Kidneys
130
FFA vs. Lactate
There is a negative correlation between lactic acid levels and FFA concentration, meaning as lactic acid increases, FFA decrease.
Both exercise and lactic acid infusion show a similar trend, suggesting that elevated lactic acid itself (independent of exercise) plays a role in suppressing FFA.
This supports the idea that lactic acid inhibits lipolysis, reducing the availability of FFA for energy metabolism.
131
osmolality
Measure of concentration of dissolved particles (e.g., proteins, ions) in body fluid compartments
Osmolality and osmosis
If compartment osmolality increase, water is drawn in
If compartment osmolality decrease, water is drawn out
132
hypothalamus and anterior pituitary
Anterior pituitary = blood connection
Portal system carries hormone directly to anterior pituitary
Releasing hormones & factors
133
hypothalamus and posterior pituitary
Posterior pituitary = neurologic connection
More of an extension of the hypothalamus
Secretes hormones made in the hypothalamus
134
Antidiuretic hormone
Released from the posterior pituitary
-Also known as vasopressin
-Produced by the hypothalamus (stored in vesicles)
-Secreted upon neural signal from hypothalamus
Reduces water loss from the body to maintain plasma volume
-Favors reabsorption of water from kidney tubules to capillaries
-Translocation of aquaporins from intracellular vesicles to collecting duct membrane
-“anti-diuresis” = less urine output
Major stimuli include an increase in plasma osmolality or a decrease in plasma volume
↑ osmolality stimulates osmoreceptors in hypothalamus
↓ plasma volume stimulates baroreceptors (pressure)
Stretch receptors located in heart (left atrium)
135
changes in plasma ADH w/ exercise
until around 60% don't see any changes in SDH in plasma bc no sweat
136
aldosterone
Released from the adrenal cortex
-Involved in maintenance of plasma Na+ and K+
-Regulation of blood volume and pressure
Kidneys secrete K+ and reabsorb Na+
-Increases activity of existing channels & pumps
-Synthesis of new ion channels & pumps
-Subsequently, increases water retention
- takes in sodium, kicks out potassium and acid
137
aldosterone stimuli and system
Stimuli for release:
↑ K+ concentration
Involves renin-angiotensin-aldosterone system:
↓ plasma volume
↓ blood pressure
↑ sympathetic nerve activity
- stimulates release of renin from kidney
138
Renin-Angiotensin-Aldosterone System
Mechanism
Renin converts angiotensinogen → angiotensin I
Angiotensin-converting enzyme (ACE) converts
angiotensin I → angiotensin II
Angiotensin II stimulates aldosterone release from the adrenal cortex
Additionally, causes blood vessels to constrict
139
changes in Aldosterone, Renin and Ang 2 w/ exercise
all increase the greater VO2 max
140
aldosterone and plasma volume w/ exercise
plasma volume decreases so aldosterone increases
141
Aldosterone and Osmosis
Na+ retention leads to incr. osmolality
incr. osmolality leads to incr. water retention
where Na moves, water follows
142
osmotic water movement function
minimizes loss of plasma volume, maintains blood pressure
- effects can persist 12-48 hours post-exercise (steroid hormone)
143
Too much blood volume
Sustained elevated blood volume triggers the release of atrial natriuretic peptide (ANP).
- Causes stretch of heart muscle (atria)
- Opposes action of aldosterone
- Increased Na+ and H2O excretion
- Decreases plasma volume
144
145
Fatigue
reduced power output during repeated muscle contractions
- related to reduced force generation and/or impaired shortening velocity
146
muscle fatigue reversibility
within a few hours of rest
- fatigue is not the same as muscle injury: damage that takes days to weeks for recover
147
muscle fatigue in high-intensity exercise
bouts of exercise that last 1-10min
very heavy/high intensity
148
muscle fatigue in high-intensity results from
impaired calcium release in muscle fibers
impaired sensitivity to calcium
149
metabolites that contribute to muscle fatigue in high-intensity
phosphate, lactate and H, free radicles
150
muscle fatigue in prolonged exercise
exercise lasting longer than 1 hour
moderate intensity
151
muscle fatigue in prolonged exercise results from
depletion of muscle glycogen
free radicals causing disruption of myosin cross-bridges (bc of oxidative phosphorylation)
152
central fatigue characterised by
impaired motivation
reduced brain arousal
reduced motor unit recruitment
153
possible causes of central fatigue
blunted depolarization of alpha motor neurons
afferent feedback from muscle
CNs neurotransmitters
- higher serotonin than dopamine leads to tiredness caused by excessive exercise
- lower serotonin than dopamine leads to brain arousal promoted by regular exercise
154
central fatigue represents what percentage of overall fatigue during exercise?
10-15%
155
peripheral fatigue energy systems involved
depletion of phosphocreatine
glycogen depletion
156
peripheral fatigue imbalance
imbalance between ATP requirements and ATP production capability
- protective function that allows ATP to still be used for baseline cellular activities
- cells do not run out of ATP
157
phosphocreatine depletion
PC depletion coincides with fatigue during very high-intensity, short-duration activities
PC depletes faster and sooner than ATP
- ATP produced by other systems
As PC becomes depleted, rapid regeneration of ATP slows, and ATP concentrations fall
158
Glycogen depletion
Glycogen reserves are limited and become depleted across 1-3 hours of exercise
Depletion is correlated with fatigue
- Related to total glycogen depletion
*Rate of depletion is more rapid at the onset of exercise rather than later stages
159
Muscle glycogen threshold for fatigue
constant rate of exercise but perceived exertion goes up because muscle glycogen decreases
- consider runners "hitting the wall"
160
glycogen depletion in different muscle groups
Activity-specific muscles are depleted fastest
- Are recruited earliest and longest for given task
161
glycogen depletion and blood glucose
Muscle glycogen insufficient for prolonged exercise
Liver glycogen → glucose into blood
As muscle glycogen ↓, liver glycogenolysis ↑
Muscle glycogen depletion + hypoglycemia = fatigue
162
Why not switch to fat oxidation after depletion?
We do, but
Lower maximal rate of ATP synthesis
More O2 required to produce ATP
Fat oxidation is unable to supply ATP at the same rate as carbohydrate oxidation can
163
Cross-bridge cycling depends on:
Functional arrangement of actin and myosin
Availability of Ca++ to bind with troponin
Availability of ATP to activate and dissociate cross-bridge
164
high concentration of H and lactate (peripheral factors may...
Reduce force per cross-bridge
Reduce force generated at a given [Ca++]
Inhibit release of Ca++ from SR
165
free radicals produced during exercise cause damage (oxidative stress) resulting in:
Damage to contractile proteins
Impaired calcium sensitivity
Reduced number of actin-myosin cross bridges
Depressed sodium/potassium pump activity in skeletal muscle
166
exercise-associated muscle cramps
Painful, spasmodic, involuntary contractions of skeletal muscles during or immediately after exercise
Localized to overworked muscle
Two theories about cause:
- Dehydration and electrolyte imbalances
- Neuromuscular dysfunction
167
dehydration and electrolyte imbalance
Abnormal electrolyte levels (ex. Na or Mg) in interstitial space surrounding nerve terminal cause uncontrolled release of acetylcholine at neuromuscular junction
Evidence against this theory:
- Dehydration/electrolyte imbalance affect entire body
- Contraction-induced cramping can occur without imbalance
- Static stretching can relieve cramp
Most likely associated with prolonged exercise in hot environment with large sweat loss (“heat cramps”)
168
Neuromuscular dysfunction
As muscle fatigue develops
- Muscle spindle becomes over-sensitive to muscle elongation
--Causes muscle contraction when it shouldn’t
-GTO becomes less sensitive to tension
--Fails to trigger reflex inhibition of muscle contraction
--Loss of inhibitory signal = unchecked muscle force generation
Relieved with stretching
- Stronger stretch signal to GTO ultimately relaxes the cramp
