Exercise Physiology

Question 1

Describe the normal energy requirements at rest.

Answer 1

• 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

Question 2

How do energy requirements change in rest-to-exercise transition?

Answer 2

• 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.

Question 3

Describe the rest-to-exercise transition.

Answer 3

• 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.

Question 4

Describe the body’s recovery from exercise.

Answer 4

• 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.

Question 5

Describe the ‘oxygen debt’ associated with exercise.

Answer 5

• ‘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)

Question 6

Describe the metabolic responses to short-term, high intensity exercise.

Answer 6

• 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

Question 7

Describe the metabolic responses to prolonged exercise.

Answer 7

• 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.

Question 8

Describe the metabolic responses to incremental exercise.

Answer 8

• 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.

Question 9

Describe the relationship between exercise intensity and fuel selection.

Answer 9

• 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

Question 10

Is low-intensity exercise best for burning fat?

Answer 10

• 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).

Question 11

What is the effect of exercise duration on muscle fuel source?

Answer 11

Question 12

Describe the immune response to infection.

Answer 12

• 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.

Question 13

How does moderate aerobic exercise protect against infection?

Answer 13

• 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

Question 14

Describe how high-intensity / long-duration aerobic exercise increases risk of infection.

Answer 14

• 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.

Question 15

Does exercise in extreme environments increase the risk of infection?

Answer 15

• 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.

Question 16

Is it okay to exercise when you have a cold?

Answer 16

• 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

Question 17

What happens to the cardiac cycle during exercise?

Answer 17

• 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.

Question 18

Describe oxygen delivery during exercise.

Answer 18

• 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

Question 19

Describe the changes in cardiac output during exercise.

Answer 19

• 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

Question 20

How does blood flow redistribute during exercise?

Answer 20

• 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.

Question 21

How is local blood flow regulated during exercise?

Answer 21

• 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.
• Vasoconstriction to visceral organs and inactive tissues.
  
  • SNS vasoconstriction.
  • Blood flow reduced to 20-30% of resting values.

Question 22

What is the difference in circulatory response between arm and leg exercise?

Answer 22

• 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

Question 23

Do respiratory muscles fatigue during exercise?

Answer 23

• Respiratory muscles do fatigue during exercise:
  
  • Prolonged (>120 minutes)
  • High-intensity (90-100% VO₂max)

Question 24

Do respiratory muscles adapt to training?

Answer 24

• Yes
• Increased oxidative capacity improves respiratory muscle endurance.
• Reduced work of breathing.

Question 25

Describe the respiratory transition from rest to work.

Answer 25

• 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.

Question 26

Describe the respiratory changes when exercising in a hot environment.

Answer 26

• 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.

Question 27

Describe the ventilation changes during incremental exercise in an untrained subject.

Answer 27

• Ventilation:
  
  • Linear increase up to ~50% - 75% VO₂max
  • Exponential increase beyind this point
  • Ventilatory threshold (Tvent)
    
    • Inflection point where V_E increases exponentially
• PO₂
  
  • Maintained within 10-12mmHg of resting value

Question 28

Describe the ventilation changes during incremental exercise in an elite athlete.

Answer 28

• 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

Question 29

Describe heat production.

Answer 29

• Voluntary
  
  • 70-80% energy expenditure appears as heat.
• Involuntary
  
  • Shivering
    
    • Increases heat production by ~5x
  • Action of hormones
    
    • Thyroxine
    • Catecholamines
    • Nonshivering thermogenesis

Question 30

Describe heat loss.

Answer 30

• 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

Question 31

How do you calculate heat loss via evaporation?

Answer 31

• Evaporation of 1,000mL of sweat results in 580Kcal of heat loss.

Question 32

Describe heat storage in the body during exercise.

Explain how to calculate body temperature increase.

Answer 32

• 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)

Question 33

What is the primary mechanism of heat loss during exercise in a cold environment?

Answer 33

Evaporation

Question 34

The rate of evaporation from the skin is dependent on 3 factors. What are they?

Answer 34

• The temperature and relative humidity
• Convective currents around the body
• Amount of skin exposed to the environment

Question 35

Describe the thermal events during exercise.

Answer 35

• 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

Question 36

What happens during exercise in a hot environment?

Answer 36

• 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

Question 37

What happens to exercise performance in a hot environment?

Why?

Answer 37

• 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

Question 38

What is heat acclimation?

How does it happen?

Answer 38

• 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

Question 39

What are the physiological adaptations during heat acclimation?

Answer 39

• 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.

Question 40

What are the physiological responses to exercise in a cold environment?

Answer 40

• 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.

Question 41

Describe cold acclimation.

Answer 41

• 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