Midterm Review Flashcards
Name the steps of muscle fibre contraction: excitation-contraction coupling.
- Action potential (AP) starts in brain
- AP arrives at axon terminal, releases acetylcholine (ACh)
- ACh crosses synapse, binds to ACh receptors on plasmalemma
- AP travels down plasmalemma, T-tubules
- Triggers Ca2+ release from sarcoplasmic reticulum (SR)
- Ca2+ enables actin-myosin contraction
How do muscles create movement?
process of actin-myosin contraction
Describe what happens during relaxed state.
- No actin-myosin interaction at binding site
- Myofilaments overlap a little
Describe what happens during contracted state.
- Myosin head pulls actin toward sarcomere center (power stroke)
- Filaments slide past each other
- Sarcomeres, myofibrils, muscle fiber all shorten
Describe what happens after power stroke ends.
- Myosin detaches from active site
- Myosin head rotates back to original position
- Myosin attaches to another active site farther down
The muscle filament process continues until:
- Z-disk reaches myosin filaments or
- AP stops, Ca2+ gets pumped back into SR
What energy is used for muscle contraction?
adenosine triphosphate (ATP)
What does ATP bind to for muscle contraction?
- binds to myosin head
- ATPase on myosin head
- ATP –> ADP + Pi + energy
What happens when AP ends?
electrical stimulation of SR stops
What is pumped back into SR for muscle relaxation? What happens with it? What is required?
- Ca 2+
- stored until next AP arrives
- requires ATP
What happens without Ca2+ for muscle relaxation?
- troponin and tropomyosin return to resting conformation
- Covers myosin-binding site
- Prevents actin-myosin cross-bridging
Approx. 50% of fibres in an average muscle are what type?
type 1
Type 1 muscle fibres hit peak tension in how long?
110 ms (slow twitch)
Type 2 muscle fibres hit peak tension in how long?
50 ms (fast twitch)
Type 2 muscle fibres make up what percent of fibres in an average muscle each?
appox. 25%
What varies between type 1 and type 2 muscle fibres?
speed of myosin ATPase
Fast myosin ATPase =
fast contraction cycling
Slower myosin ATPase =
slower contraction cycling
What happens during a muscle biopsy?
- Small (10-100 g) piece of muscle removed
- Frozen, sliced, examined under microscope
What is gel electrophoresis?
- Type I versus II fibers have different types of myosin
- Separates different types of myosin by size
How do type 1 and type 2 fibres vary in terms of SR?
- Type II fibers have a more highly developed SR
- Faster Ca2+ release, 3 to 5 times faster Vo
How do type 1 and type 2 fibres vary in terms of motor units?
- Type I motor unit: smaller neuron, <300 fibers
- Type II motor unit: larger neuron, >300 fibers
What are the 2 types of muscle contraction?
- static (isometric) contraction
- dynamic contraction
Describe static (isometric) contraction.
- Muscle produces force but does not change length
- Joint angle does not change
- Myosin cross-bridges form and recycle, no sliding
Describe dynamic contraction.
- Muscle produces force and changes length
- Joint movement produced
Describe motor unit recruitment for type 1 and type 2 motor units.
- type 1 motor units = less force
- type 2 motor units = more force
- fewer small fibres versus more large fibres
What are the 3 different frequency of stimulation (rate coding)?
- twitch
- summation
- tetanus
What is the length-tension relationship?
- Optimal sarcomere length = optimal overlap
- Too short or too stretched = little or no force develops
What is the speed-force relationship?
- Concentric: maximal force development decreases at higher speeds
- Eccentric: maximal force development increases at higher speeds
Define substrates.
- Fuel sources from which we make energy (adenosine triphosphate [ATP])
- Carbohydrate, fat, protein
Define bioenergetics.
- Process of converting substrates into energy
- Performed at cellular level
Define metabolism.
chemical reactions in the body
How can we calculate energy release?
can be calculated from heat produced
1 calorie (cal) =
heat energy required to raise 1 g of water from 14.5 °C to 15.5 °C
1000 cal =
1 kcal = 1 Calorie (dietary)
What are substrates?
- fuel for exercise
- carbohydrate, fat, protein
- carbon, hydrogen, oxygen, nitrogen
Energy from chemical bonds in food stored in what?
high energy compound ATP
Resting: ___% carbohydrate, ___% fat
50% carbohydrate, 50% fat
Exercise (short):
more carbohydrate
Exercise (long):
carbohydrate, fat
All carbohydrate converted to:
glucose
What happens with carbohydrate that have been converted to glucose?
- 4.1 kcal/g; ~2,500 kcal stored in body
- Primary ATP substrate for muscles, brain
- Extra glucose stored as glycogen in liver, muscles
When is glycogen converted back to glucose?
when needed to make more ATP
Describe glycogen stores.
- limited (2500 kcal)
- must rely on dietary carbohydrate to replenish
What is the energy substrate during starvation?
protein
What happens with protein used as energy?
- 4.1 kcal/g
- Must be converted into glucose (gluconeogenesis)
Protein can also be converted into what? What is this used for?
- FFAS (lipogenesis)
- For energy storage
- For cellular energy substrate
Energy is released at a controlled rate based on what?
- availability of primary substrate
- enzyme activity in metabolic pathway
What is the mass action effect?
- Substrate availability affects metabolic rate
- More available substrate = higher pathway activity
- Excess of given substrate = cells rely on that energy substrate more than others
Name 4 characteristics of enzymes.
- Do not start chemical reactions or set ATP yield
- Do facilitate breakdown (catabolism) of substrates
- Lower the activation energy for a chemical reaction
- End with suffix -ase
ATP is broken down by:
ATPase
Enzymes determine ____ yield.
ATP yield
Each step in a biochemical pathway requires specific ______.
enzyme(s)
More enzyme activity =
more product
What is rate-limiting enzyme?
- Can create bottleneck at an early step
- Activity influenced by negative feedback
- Slows overall reaction, prevents runaway reaction
Why must the body constantly synthesize new ATP?
ATP storage is limited
What are the 3 ATP synthesis pathways?
- ATP-PCr system (anaerobic metabolism)
- Glycolytic system (anaerobic metabolism)
- Oxidative system (aerobic metabolism)
What type of system is the ATP-PCr system?
- anaerobic
- substrate level metabolism
What is the duration of the ATP-PCr system?
3 to 15s
What pathway is used to reassemble ATP because ATP stores are very limited?
ATP-PCr system
How does phosphocreatine (PCr): ATP recycling work?
- PCr + creatine kinase –> Cr + Pi + energy
- PCr energy cannot be used for cellular work
- PCr energy can be used to reassemble ATP
The ATP-PCr system replenishes what?
ATP stores during rest
The ATP-PCr system recycles ATP during _____ until _____.
recycles ATP during exercise until used up (~3-15 s maximal exercise)
What type of system is the glycolytic system?
anaerobic
What is the duration of the glycolytic system?
- 15s to 2 min.
- need another pathway for longer durations
The glycolytic system is the breakdown of ______.
glucose via glycolysis
How does the glycolytic system use glucose or glycogen as its substrate?
- Must convert to glucose-6-phosphate
- Costs 1 ATP for glucose, 0 ATP for glycogen
The glycolytic system pathway starts with ____, ends with _____.
starts with glucose-6-phosphate, ends with pyruvic acid\
The glycolytic system has how many enzymatic reactions total?
10-12
Where does the glycolytic system occur?
all steps occur in cytoplasm
What is the ATP yield for glycolytic system?
- 2 ATP for glucose
- 3 ATP for glycogen
What are the pros of the glycolytic system?
- Allows muscles to contract when O2 limited
- Permits shorter-term, higher-intensity exercise than oxidative metabolism can sustain
What are the cons of the glycolytic system?
- Low ATP yield, inefficient use of substrate
- Lack of O2 converts pyruvic acid to lactic acid
- Lactic acid impairs glycolysis, muscle contraction
What is Phosphofructokinase (PFK)?
- rate limiting enzyme
- dec. ATP (inc. ADP) –> inc. PFK activity
- inc. ATP –> dec. PFK activity
- also regulated by products of Krebs cycle
Glycolysis will give you ~ ___ min maximal exercise.
~2 minutes
What type of system is the oxidative system?
aerobic
What is the ATP yield of the oxidative system?
- depends on substrate
- 32 to 33 ATP/1 glucose
- 100+ ATP/1 FFA
What is the duration of the oxidative system?
steady supply for hours
Which is the most complex of the 3 bioenergetic systems?
oxidative system
Where does the oxidative system occur?
in the mitochondria, not cytoplasm
What are the 3 stages of oxidation of carbohydrate?
- Stage 1: Glycolysis
- Stage 2: Krebs cycle
- Stage 3: Electron transport chain
Which systems interact for all activities?
- all 3 systems
- no one system contributes 100%
- one system often dominates for a given task
Type 1 fibres have _____ oxidative capacity. Why?
- greater
- more mitochondria
- high oxidative enzyme concentrations
- type II better for glycolytic energy production
Describe how endurance training effects fibre type composition.
- enhances oxidative capacity of type II fibres
- develops more (and larger) mitochondria
- more oxidative enzymes per mitochondrion
As intensity goes up, so does …
ATP demand
What happens in response to increased intensity?
- Rate of oxidative ATP production increases
- O2 intake at lungs increases
- O2 delivery by heart, vessels increases
O2 storage is limited, meaning:
use it or lose it
What is a accurate estimate of O2 use in muscle?
O2 levels entering and leaving the lungs
The sensory division transmits information from ______ to _____.
periphery to brain
What are the 5 major families of sensory receptors?
- Mechanoreceptors: physical forces
- Thermoreceptors: temperature
- Nociceptors: pain
- Photoreceptors: light
- Chemoreceptors: chemical stimuli
Name 3 special families of sensory receptors.
- joint kinesthetic receptors
- muscle spindles
- golgi tendon organs
Joint kinesthetic receptors are sensitive to:
joint angles, rate of angle change
Joint kinesthetic receptors sense:
joint position, movement
Muscle spindles are sensitive to:
muscle length, rate of length change
Muscle spindles sense:
muscle stretch
Golgi tendon organs are sensitive to:
tension in tendon
Golgi tendon organs sense:
strength of contraction
The motor division transmits information from _____ to _____.
brain to periphery
What are the 2 divisions of the motor division?
- autonomic: regulates visceral activity
- somatic: stimulates skeletal muscle activity
The autonomic nervous system controls:
involuntary internal functions
Name some exercise-related autonomic regulation.
- HR, BP
- lung function
What are the 2 complementary divisions of the autonomic nervous system.
- sympathetic nervous system
- parasympathetic nervous system
Describe the sympathetic division of the autonomic nervous system.
- fight or flight
- prepares body for exercise
Sympathetic stimulation results in:
- increased HR, BP
- increased blood flow to muscles
- increased airway diameter (bronchodilation)
- increased metabolic rate, glucose levels, FFA levels
- increased mental activity
Describe the parasympathetic division of the autonomic nervous system.
- rest and digest
- active at rest
- opposes sympathetic effects
Parasympathetic stimulation results in:
- increased digestion, urination
- conservation of energy
- decreased heart rate
- decreased diameter of vessels and airways
A _____ ______ carries AP to muscle.
motor neuron
AP spreads to _____ ______ of motor unit.
muscle fibres
Fine motor control means _____ fibres per motor unit.
fewer
Gross motor control means _____ fibres per motor unit.
more
Describe the homogeneity of motor units.
- Fiber types not mixed within a given motor unit
- Either type I fibers or type II fibers
- Motor neuron may actually determine fiber type
Nervous system = ______ communication.
electrical
Endocrine system = ______ communication.
chemical
The endocrine system is _____ responding and _____ lasting than the nervous system.
- slower responding
- longer lasting
The endocrine system maintains homeostasis via ______.
hormones
What are hormones?
- chemicals that control and regulate cell/organ activity
- act on target cells
The endocrine system constantly monitors ____ ____.
internal environment
The endocrine system coordinates…
integration of physiological systems during rest and exercise
The endocrine system maintains ______ during exercise.
homeostasis
How does the endocrine system maintain homeostasis during exercise?
- controls substrate metabolism
- regulates fluid, electrolyte balance
______ is appetite control centre of brain.
hypothalamus
Satiety centre is in _____ _____.
ventromedial nucleus
Hunger centre is in _____ _____.
lateral hypothalamus
___ _____ releases hormones that affect hunger signals.
GI tract
What is cholecyctokinin (CCK)?
- stimulated when stomach is full
- decreases appetite
What is glucagon-like peptide (GLP-1)?
- released in small intestine
- decreases appetite
What is peptide YY (PYY)?
- released in small intestine
- decreases appetite
What is ghrelin?
increases appetite
Adipose is an _____ organ.
endocrine
Leptin is released from where? What does it do?
- released from adipose stores
- reduces hunger
Leptin and ghrelin act in _______ ways.
opposing
Obese people have higher ____. Why doesn’t this work properly?
- leptin
- resistant to effects
*_____ affects hunger and satiety hormones.
exercise
*Acute, vigorous exercise increases ____ and ___, doing what to hunger?
- PYY and GLP-1
- reducing hunger
*How does exercise training affect ghrelin?
does not affect it except in energy deficit
Looking at substrate metabolism efficiency, 40% of substrate energy –>
ATP
Looking at substrate metabolism efficiency, 60% of substrate energy –>
heat
Heat production increases with _____ production.
energy
How can energy expenditure be measured with direct calorimetry?
- Can be measured in a calorimeter
- Water flows through walls
- Body temperature increases water temperature
What are the pros of measuring energy expenditure with direct calorimetry?
- Accurate over time
- Good for resting metabolic measurements
What are the cons of measuring energy expenditure with direct calorimetry?
- Expensive, slow
- Exercise equipment adds extra heat
- Sweat creates errors in measurements
- Not practical or accurate for exercise
How can energy expenditure be measured indirectly?
- estimate total body energy expenditure based on O2 used, CO2 produced
- measures respiratory gas concentrations
- only accurate for steady-state oxidative metabolism
Older methods of measuring energy expenditure indirectly are ______ but ____.
accurate but slow
New methods of measuring energy expenditure indirectly are ______ but ____.
faster but expensive
What is VO2?
- volume of O2 consumed per minute
- rate of O2 consumption
- volume of inspired O2 [minus] volume of inspired CO2
What is VCO2?
- volume of CO2 produced per minute
- rate of CO2 production
- volume of expired CO2 [minus] volume of inspired CO2
What are 3 ways of measuring energy expenditure?
- directly
- indirectly
- respiratory exchange ratio
O2 usage during metabolism depends on…
type of fuel being oxidized
More carbon atoms in molecule =
more O2 needed
Glucose (C6H12O6) < ______
palmitic acid (C16H32O2)
What is the respiratory exchange ratio (RER)?
- Ratio between rates of CO2 production, O2 usage
- RER = VCO2 / VO2
RER for 1 molecule glucose =
1.0
Work out why RER for 1 molecule glucose is 1.0.
- 6 O2 + C6H12O6–> 6 CO2 + 6 H2O + 32 ATP
- RER = VCO2 / VO2 = 6 CO2/6 O2 = 1.0
RER for 1 molecule palmitic acid =
0.70
Work out why RER for 1 molecule palmitic acid is 0.70.
- 23 O2 + C16H32O2 –> 16 CO2 + 16 H2O + 129 ATP
- RER = VCO2 / VO2 = 16 CO2/23 O2 = 0.70
The RER predicts:
- substrate use
- kilocalories/O2 efficiency
Name 4 indirect calorimetry limitations.
- CO2 production may not = CO2 exhalation
- RER inaccurate for protein oxidation
- RER near 1.0 may be inaccurate when lactate buildup ( ) CO2 exhalation
- Gluconeogenesis produces RER <0.70
What is metabolic rate?
rate of energy use by body
Based on whole-body O2 consumption and corresponding caloric equivalent, what is RER at rest?
~0.80
Based on whole-body O2 consumption and corresponding caloric equivalent, what is VO2 at rest?
~0.3 L/min
Based on whole-body O2 consumption and corresponding caloric equivalent, what is metabolic rate at rest?
~2000 kcal/day
What is basal metabolic rate (BMR)?
rate of energy expenditure at rest
When is BMR taken?
- In supine position
- Thermoneutral environment
- After 8 h sleep and 12 h fasting
Minimum energy requirement for living is related to…
fat-free mass (kcal x kg FFM^-1 x min^-1)
Name 5 factors that affect BMR.
- body SA
- age
- stress
- hormones
- body temperature
What is resting metabolic rate (RMR)?
- Similar to BMR (within 5-10% of BMR) but easier
- Doesn’t require stringent standardized conditions
- 1,200 to 2,400 kcal/day
Total daily metabolic activity includes…
normal daily activities
What is the normal range for total daily metabolic activity?
1800 to 3000 kcal/day
What is the total daily metabolic activity range for competitive athletes?
up to 10,000 kcal/day
Metabolic rate increases with _____ _____.
exercise intensity
Slow component of O2 uptake kinetics during submaximal aerobic exercise means:
- At high power outputs, VO2 continues to increase
- More type II (less efficient) fiber recruitment
What is VO2 drift?
- Upward drift observed even at low power outputs
- Possibly due to ventilatory, hormone changes?
What is VO2 max?
- maximal O2 uptake
- Point at which O2 consumption doesn’t increase with further increase in intensity
- Best single measurement of aerobic fitness
- Not best predictor of endurance performance
When does VO2 max plateau?
after 8 to 12 weeks of training
What allows athletes to compete at higher percentage of VO2 max?
more training
VO2 max is expressed in:
- L/min
- easy standard units
- suitable for non-weight-bearing activities
What is the VO2 max for untrained young men?
44-50 L/min
What is the VO2 max for untrained young women?
38-42 L/min
Why is there a sex difference in VO2 max?
women’s lower FFM and hemoglobin
Can any activity be 100% aerobic or anaerobic?
no
Estimates of anaerobic effort involve:
- excess postexercise O2 consumption
- lactate threshold
What is postexercise O2 consumption?
- O2 demand > O2 consumed in early exercise
- O2 consumed > O2 demand in early recovery
If O2 demand > O2 consumed in early exercise, what happens?
- Body incurs O2 deficit
- O2 required − O2 consumed
- Occurs when anaerobic pathways used for ATP production
If O2 consumed > O2 demand in early recovery, what happens?
- Excess postexercise O2 consumption (EPOC)
- Replenishes ATP/PCr stores, converts lactate to glycogen, replenishes hemo/myoglobin, clears CO2
What is lactate threshold?
point at which blood lactate accumulation increases markedly
When lactate threshold is reached, lactate production rate > ____ _____ ____.
lactate clearance rate
Lactate threshold is an interaction of _____ and _____ systems.
aerobic and anaerobic
Lactate threshold is a good indicator of …
potential for endurance exercise
Lactate threshold is usually expressed as:
percentage of VO2 max
Higher lactate threshold =
better endurance performance
For 2 athletes with the same VO2 max, higher lactate threshold predicts…
better performance
Why is anaerobic capacity hard to measure?
no clear, VO2 max like method for measuring anaerobic capacity
Name 3 imperfect but accepted methods for measuring anaerobic capacity?
- maximal accumulated O2 deficit
- wingate anaerobic test
- critical power test
What are the 2 definitions of fatigue?
- Decrements in muscular performance with continued effort, accompanied by sensations of tiredness
- Inability to maintain required power output to continue muscular work at given intensity
Fatigue is reversible by ____.
rest
Fatigue can be caused by:
- metabolic by-products
- muscle soreness
How does heat alter metabolic rate?
- increased rate of carbohydrate utilization
- hastens glycogen depletion
- high muscle temperature may impair muscle function
At what temperature is time to exhaustion longest?
11 degrees celsius
At what temperature is time to exhaustion shortest?
31 degrees celsius
Muscle ______ prolongs exercise.
precooling
Where does muscle soreness come from?
exhaustive or high-intensity exercise, especially the first time performing a new exercise
When is muscle soreness felt?
- can be felt anytime
- acute soreness during and immediately after exercise
- delayed-onset soreness one to two days later
What is DOMS?
delayed-onset muscle soreness
When is DOMS felt?
1-2 days after exercise bout
What does DOMS feel like?
ranges from stiffness to severe, restrictive pain
What is a major cause of DOMS? What is it not caused by? Give an example.
- caused by eccentric contractions
- ex. level run pain < downhill run pain
- not caused by blood lactate concentrations
Describe the sequence of events in DOMS.
- high tension in muscle = structural damage to muscle, cell membrane
- membrane damage disturbs Ca 2+ homeostasis in injured fibre
- after a few hours, circulating neutrophils
- products of macrophage activity, intracellular contents accumulate
- fluids and electrolytes shift into the area, creating edema
What happens when membrane damage disturbs Ca 2+ homeostasis in injured fibre?
- inhibits cellular respiration
- activates enzymes that degrade z-discs
What happens when intracellular contents accumulate?
- histamine, kinins, K+
- stimulate pain in free nerve endings
DOMS = ______ muscle force generation
decreased
DOMS results in loss of strength because of 3 factors:
- physical disruption of muscle
- failure in excitation-contraction coupling (appears to be most important)
- loss of contractile protein
Name 3 strategies to reduce DOMS.
- Minimize eccentric work early in training
- Start with low intensity and gradually increase
- Start with high-intensity, exhaustive training (soreness bad at first, much less later on)
