Flashcards in Midterm Review Deck (212):
Name the steps of muscle fibre contraction: excitation-contraction coupling.
1. Action potential (AP) starts in brain
2. AP arrives at axon terminal, releases acetylcholine (ACh)
3. ACh crosses synapse, binds to ACh receptors on plasmalemma
4. AP travels down plasmalemma, T-tubules
5. Triggers Ca2+ release from sarcoplasmic reticulum (SR)
6. 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 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?
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)?
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
- Fuel sources from which we make energy (adenosine triphosphate [ATP])
- Carbohydrate, fat, protein
- Process of converting substrates into energy
- Performed at cellular level
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
All carbohydrate converted to:
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?
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:
Enzymes determine ____ yield.
Each step in a biochemical pathway requires specific ______.
More enzyme activity =
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?
- 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?
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?
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?
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.
What type of system is the oxidative system?
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?
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?
- 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 ...
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:
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.
AP spreads to _____ ______ of motor unit.
Fine motor control means _____ fibres per motor unit.
Gross motor control means _____ fibres per motor unit.
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.
Endocrine system = ______ communication.
The endocrine system is _____ responding and _____ lasting than the nervous system.
- slower responding
- longer lasting
The endocrine system maintains homeostasis via ______.
What are hormones?
- chemicals that control and regulate cell/organ activity
- act on target cells
The endocrine system constantly monitors ____ ____.
The endocrine system coordinates...
integration of physiological systems during rest and exercise
The endocrine system maintains ______ during exercise.
How does the endocrine system maintain homeostasis during exercise?
- controls substrate metabolism
- regulates fluid, electrolyte balance
______ is appetite control centre of brain.
Satiety centre is in _____ _____.
Hunger centre is in _____ _____.
___ _____ releases hormones that affect hunger signals.
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?
Adipose is an _____ organ.
Leptin is released from where? What does it do?
- released from adipose stores
- reduces hunger
Leptin and ghrelin act in _______ ways.
Obese people have higher ____. Why doesn't this work properly?
- resistant to effects
*_____ affects hunger and satiety hormones.
*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 -->
Looking at substrate metabolism efficiency, 60% of substrate energy -->
Heat production increases with _____ production.
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?
- 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 =
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 =
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?
Based on whole-body O2 consumption and corresponding caloric equivalent, what is VO2 at rest?
Based on whole-body O2 consumption and corresponding caloric equivalent, what is metabolic rate at rest?
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
- 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 _____ _____.
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?
VO2 max is expressed in:
- easy standard units
- suitable for non-weight-bearing activities
What is the VO2 max for untrained young men?
What is the VO2 max for untrained young women?
Why is there a sex difference in VO2 max?
women's lower FFM and hemoglobin
Can any activity be 100% aerobic or anaerobic?
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...
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 ____.
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.
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.
1. high tension in muscle = structural damage to muscle, cell membrane
2. membrane damage disturbs Ca 2+ homeostasis in injured fibre
3. after a few hours, circulating neutrophils
4. products of macrophage activity, intracellular contents accumulate
5. 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
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