Exercise Physiology Flashcards
1
Q
Describe the normal energy requirements at rest.
A
- Almost 100% of ATP is produced by anaerobic metabolism.
- Blood lactate levels are low (<1.0 mmol/L).
- Resting consumption:
- 0.25 L/min
- 3.5 mL/kg/min
2
Q
How do energy requirements change in rest-to-exercise transition?
A
- ATP production increases immediately.
- Oxygen uptake increases rapidly.
- Reaches steady state within 1-4 minutes.
- After steady state is reached, ATP requirement is met through aerobic ATP production.
- Initial ATP production through anaerobic pathways.
- ATP-PC system
- Glycolysis
- Oxygen defecit
- Lag in oxygen uptake at the beginning of exercise.
3
Q
Describe the rest-to-exercise transition.
A
- In the transition from rest to light-moderate exercise, oxygen uptake increases rapidly, generally reaching a steady state within 1-4 minutes.
- The term ‘oxygen defecit’ applies to the lag in oxygen uptake at the beginning of exercise.
- The failure of oxygen uptake to increase instantly at the beginning of exercise suggests that anaerobic pathways contribute to the overall production of ATP early in exercise.
- After a steady state is reached, the body’s ATP requirement is met via aerobic metabolism.
4
Q
Describe the body’s recovery from exercise.
A
- Oxygen uptake remains elevated above rest during recovery.
- Oxygen debt - repayment for O2 defecit at onset of exercise.
- Excess post-exercise consumption (EPOC) - terminology reflects that only ~20% elevated O2 consumption is used to ‘repay’ O2 defecit.
5
Q
Describe the ‘oxygen debt’ associated with exercise.
A
- ‘Rapid’ portion of O2 debt
- Resynthesis of stored PC
- Replenishing muscle and blood O2 stores
- ‘Slow’ portion of O2 debt
- Elevated heart rate and breathing = ↑ energy requirement
- Elevated body temperature = ↑ metabolic rate
- Elevated epinephrine and norepinephrine = ↑ metabolic rate
- Conversion of lactic acid to glucose (gluconeogenesis)
6
Q
Describe the metabolic responses to short-term, high intensity exercise.
A
- First 1-5 seconds of exercise
- ATP produced via ATP-PC system
- Intense exercise longer than 5 seconds:
- Shift to ATP production via glycolysis
- Events lasting longer than 45 seconds:
- ATP procudtion through ATP-PC, glycolysis, and aerobic systems
- 70% anaerobic / 30% aerobic at 60 seconds
- 50% anaerobic / 50% aerobic at 2 minutes
7
Q
Describe the metabolic responses to prolonged exercise.
A
- Prolonged exercise (>10 minutes)
- ATP production primarily from aerobic metabolism
- Steady-state oxygen uptake can generally be maintained during submaximal exercise (below lactate threshold).
- Prolonged exercise in a hot / humid environment or at high intensity
- Results in upwards drift in oxygen uptake over time due to increases in body temperature and increasing blood levels of epinephrine and norepinephrine.
8
Q
Describe the metabolic responses to incremental exercise.
A
- Oxygen uptake increases linearly until maximal oxygen uptake (VO2max) is reached.
- No further increase in VO2 with increasing work rate.
- VO2max
- Physiological ceiling for delivery of O2 to muscle.
- Affected by genetics and training.
- Physiological factors influencing VO2max:
- Maximum ability of cardiorespiratory system to deliver oxygen to the muscle.
- Ability of muscles to use oxygen and produce ATP aerobically.
9
Q
Describe the relationship between exercise intensity and fuel selection.
A
- Low-intensity exercise (<30% VO2max)
- Fats are primary fuel during prolonged low intensity exercise.
- High-intensity exercise (<70% VO2max)
- Carbohydrates are primary fuel.
- The ‘crossover’ concept
- Describes the shoft from fat to CHO metabolism as exercise intensity increases.
- Due to:
- Recruitment of fast muscle fibres
- Increasing blood levels of epinephrine
10
Q
Is low-intensity exercise best for burning fat?
A
- At low exercise intensities (~20% VO2max)
- High percentage of energy expenditure (~66%) derived from fat.
- However, total energy expenditure is low (3kCal / min).
- Total fat oxidation is also low (2kCal / min).
- At higher exercise intensities (~60% VO2max)
- Lower percentage of energy (~33%) from fat.
- Total energy expended is higher (9kCal / min).
- Total fat oxidation is also higher (3 kCal / min).
11
Q
What is the effect of exercise duration on muscle fuel source?
A
12
Q
Describe the immune response to infection.
A
- Exercise can have a positive and negative effect on upper respiratory tract infection (URTI).
- J-shaped curve:
- People who engage in regular moderate exercise are at lower risk of URTI.
- Risk is higher in people who engage in intense and / or long-duration exercise and people who do not exercise.
13
Q
How does moderate aerobic exercise protect against infection?
A
- Regular exercise reduces risk of URTI 18-67%
- 20-40 minutes of exercise at 40-60% VO2max is sufficient.
- Resistance exercise may also be beneficial.
- Mechanisms
-
Exercise boosts innate immune system
- Natural killer cells and neutrophils
- Returns to normal level in ~3 hours
-
Other factors associated with exercise
- Less emotional stress
- Better nutrition
- Adequate sleep
-
Exercise boosts innate immune system
14
Q
Describe how high-intensity / long-duration aerobic exercise increases risk of infection.
A
- Prolonged exercise (>90 minutes) has a temporary depresive effect on the immune system.
- Decreased levels of B cells, T cells and NK cells.
- Decreased NK cell activity and T cell function.
- Decreased nasal neutrophil phagocytosis.
- Decreased nasal and salivary IgA.
- Increased pro- and anti- inflammatory cytokines.
- ‘Open window’ of increased risk of infection.
- May be caused by high cortisol levels.
- May also be due to other factors - lack of sleep, mental stress, increased exposure to pathogens.
15
Q
Does exercise in extreme environments increase the risk of infection?
A
- Exercise in hot environment
- Elevated levels of cortisol compared to cool environment.
- No impairment of immune function.
- Exercise in the cold
- Does not have negative effect on immune system.
- Exercise at high altitude (>6000 feet)
- Increased levels of cortisol.
- Does not impair immune function in the lab.
- In the field, increased risk of URTI at high altitude.
16
Q
Is it okay to exercise when you have a cold?
A
- It is fine to exercise if cold symptoms are above the neck.
- Runny nose, nasal congestion, mild sore throat.
- Reduce intensity / duration of workout.
- Should not exercise if symptoms are below the neck.
- Chest congestion, cough, abdominal pain.
- Do not exercise with:
- Fever
- Fatigue
- Widespread muscle aches
17
Q
What happens to the cardiac cycle during exercise?
A
- Systole
- Contraction phase
- Ejection of blood
- Diastole
- Relaxation phase
- Filling with blood
- At rest, diastole is longer than systole.
- During exercise, both systole and diastole are shorter.
18
Q
Describe oxygen delivery during exercise.
A
- Oxygen demand by muscles during exercise is 15-25x greater than at rest.
- Increased O2 delivery accomplished by:
- Increased CO
- Redistribution of blood flow
- From inactive organs to working skeletal muscle
19
Q
Describe the changes in cardiac output during exercise.
A
- CO increases due to:
- Increased HR
- Linear increase to max
- For adults: max HR = 220 - age (years)
- For children: max HR = 208 - 0.7 x age (years)
- Increased SV
- Increase, then plateau at 40-60% VO2max
- No plateau in highly trained subjects
- Increased HR
20
Q
How does blood flow redistribute during exercise?
A
- Increased blood flow to working skeletal muscle.
- At rest, 15-20% of CO to muscle.
- Increases to 80-85% during maximal exercise.
- Decreased blood flow to less active organs.
- Liver, kidneys, GI tract.
- Redistribution depends on metabolic rate.
- Exercise intensity.
21
Q
How is local blood flow regulated during exercise?
A
- Skeletal muscle vasodilation.
- Autoregulation
- Blood flow increased to meet metabolic demands of tissue.
- Due to changes in O2 tension, CO2 tension, nitric oxide, potassium, adenosine and pH.
- Autoregulation
- Vasoconstriction to visceral organs and inactive tissues.
- SNS vasoconstriction.
- Blood flow reduced to 20-30% of resting values.
22
Q
What is the difference in circulatory response between arm and leg exercise?
A
- At the same oxygen uptake, when compared to leg work, arm work results in higher:
- Heart rate
- Due to higher sympathetic stimulation
- Blood pressure
- Due to vasoconstriction of large inactive muscle mass
- Heart rate
23
Q
Do respiratory muscles fatigue during exercise?
A
- Respiratory muscles do fatigue during exercise:
- Prolonged (>120 minutes)
- High-intensity (90-100% VO2max)
24
Q
Do respiratory muscles adapt to training?
A
- Yes
- Increased oxidative capacity improves respiratory muscle endurance.
- Reduced work of breathing.
25
Describe the respiratory transition from rest to work.
* At the onset of constant load submaximal exercise:
* Initially, ventilation increases rapidly.
* Then, a slower rise toward steady state.
* PO2 and PCO2 are relatively unchanged.
* Slight decrease in PO2 and increase in PCO2.
* Suggests that increase in alveolar ventilation is slower than increased metabolism.
26
Describe the respiratory changes when exercising in a hot environment.
* During prolonged submaximal exercise in a hot / humid environment:
* Ventilation tends to drift upward
* Increased blood temperature affects respiratory control centre.
* Little changes in PCO2
* Higher ventilation not due to increased PCO2.
27
Describe the ventilation changes during incremental exercise in an untrained subject.
* Ventilation:
* Linear increase up to ~50% - 75% VO2max
* Exponential increase beyind this point
* Ventilatory threshold (Tvent)
* Inflection point where VE increases exponentially
* PO2
* Maintained within 10-12mmHg of resting value
28
Describe the ventilation changes during incremental exercise in an elite athlete.
* Ventilation
* Tvent occurs at higher % VO2max
* PO2
* Decrease of 30-40mmHg at near-maximal work
* Hypoxaemia
* Due to:
* Ventilation / perfusion mismatch
* Short RBC transit time in pulmonary capillary due to high cardiac output
29
Describe heat production.
* Voluntary
* 70-80% energy expenditure appears as heat.
* Involuntary
* Shivering
* Increases heat production by ~5x
* Action of hormones
* Thyroxine
* Catecholamines
* Nonshivering thermogenesis
30
Describe heat loss.
* Radiation
* Transfer of heat via infrared rays
* 60% heat loss at rest
* Can be a method of heat gain
* Conduction
* Heat loss due to contact with another surface
* Convection
* Heat transferred to air or water
* Example: a fan pushng air past skin
* Evaporation
* Heat from skin converts water (sweat) to water vapor
* Requires vapor pressure gradient between skin and air.
* Evaporation depends on:
* Temperature and relative humidity
* Convection currents around the body
* Amount of skin surface exposed
* Body loses 0.58Kcal heat / mL sweat evaporated
* 1L sweat results in heat loss of 580Kcal
* 25% heat loss at rest
* Most important means of heat loss during exercise
31
How do you calculate heat loss via evaporation?
* Evaporation of 1,000mL of sweat results in 580Kcal of heat loss.
32
Describe heat storage in the body during exercise.
Explain how to calculate body temperature increase.
* Heat produced that is not lost is stored in body tissues.
* This will raise body temperature.
* Body heat gain during exercise = (heat produced - heat lost).
* Amount of heat required to raise the body temperature:
* Specific heat of human body is 0.83Kcal / kg.
* **Heat required to raise body temperature by 1°C = (specific heat x body mass)**
33
What is the primary mechanism of heat loss during exercise in a cold environment?
Evaporation
34
The rate of evaporation from the skin is dependent on 3 factors. What are they?
* The temperature and relative humidity
* Convective currents around the body
* Amount of skin exposed to the environment
35
Describe the thermal events during exercise.
* As exercise intensity increases:
* Heat production increases
* Linear increase in body temperature
* Core temperatire proportional to active muscle mass
* Higher net heat loss
* Lower convective and radiant heat loss
* Higher evaporative heat loss
* As ambient temperature increases:
* Heat production remains constant
* Lower convective and radiant heat loss
* Higher evaporative heat loss
36
What happens during exercise in a hot environment?
* Results in reduced ability to lose body heat
* Higher core temperature
* Risk of hyperthermia and heat injury
* Higher sweat rate
* May be as high as 4-5L / hour
* Risk of dehydration
37
What happens to exercise performance in a hot environment?
Why?
* **Exercise performance in a hot environment is IMPAIRED** due to these 3 factors:
1. Accelerated muscle fatigue
* Increased glycogen breakdown
* Increased production of free radicals
* Afferent feedback from metaboreceptors in the fatiguing muscles to the brain can result in decreased central motor drive
2. Cardiovascular dysfunction
* CV strain (increased HR and decreased SV)
* Reduced muscle blood flow occurs during high intensity exercise in a hot environment
3. Central nervous system dysfunction
* Hyperthermia can impair brain function
* Dehydration can also impair brain function
* Afferent feedback from metaboreceptors in the fatiguing muscles to the brain can result in a decreased central motor drive
38
What is heat acclimation?
How does it happen?
* Acclimation
* Rapid adaptation (days to weeks) to environmental change.
* Acclimatisation
* Adaptation over a long time period (weeks to months).
* Requires exercise in a hot environment
* Elevated core temperature promotes adaptations.
* Acclimation lost within a few days of inactivity or no heat exposure
* Significant decline in 7 days
* Complete loss in 28 days
39
What are the physiological adaptations during heat acclimation?
* 10-12% increased plasma volume.
* Maintains blood volume, stroke volume and sweating capacity.
* Earlier onset of sweating and higher sweat rate
* Less heat storage, maintain lower body temperature.
* Reduced sodium chloride loss in sweat
* Reduced risk of electrolyte disturbance.
* Reduced skin blood flow
* Increased cellular heat shock proteins
* Prevent cellular damage due to heat.
40
What are the physiological responses to exercise in a cold environment?
* Combination of proper clothing and increased metabolic heat production during exercise reduces risk of hypothermia.
* Swimming in cold water can overpower the body's ability to prevent heat loss and hypothermia can occur.
* Subcutaneous fat improves cold tolerance and reduces heat loss.
* Age can impact cold tolerance during exercise
* Compared to adults, children often have a large surface-to-mass ratio which results in increased heat loss.
* Compared to young healthy adults, elderly individuals who have lost a significant amount of muscle mass due to sarcopaenia are at greater risk for hypothermia during cold exposure.
41
Describe cold acclimation.
* Resuts in lower skin temperature at which shivering begins
* Increased nonshivering thermogenesis.
* Maintain higher hand and foot temperatire
* Improved peripheral blood flow.
* Improved ability to sleep in the cold
* Due to reduced shivering.
* Adaptations begin in one week
