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exercise physiology and pharmacology > limitations to exercise > Flashcards

limitations to exercise Flashcards

1
Q

what is RQ, how is it calculated and what assumptions are required for this?

A

RQ is an indicator of the substrate use in tissues, it cannot exceed 1. it is represented as RQ = VCO2 /VO2
we assume:
the rate of O2/CO2 exchange in the lungs is equal to the rate of O2/CO2 use/release in the tissues

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2
Q

when might the rate of O2/Co2 exchange in the lungs match that of release in the tissues?

A

1- hyperventilation
2- exhaustive activity
3- gluconeogenesis

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3
Q

what is the difference between respiratory quotient and respiratory exchange ratio?

A

RQ indicates substrate use in tissues, and cannot exceed 1

RER reflects the respiratory exchange of CO2 and O2, it can exceed 1, and does during strenuous exercise

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4
Q

what is sub maximal exercise?

A
  • HR is 50-80% of maximal capacity
  • aerobic capacity is not reached
  • Vo2 should plateau
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5
Q

why is Vo2 sometimes not constant during sub maximal exercise?

A

1 - slow component of VO2 uptake kinetics

2- Vo2 drift

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6
Q

what is meant by the ‘slow component of VO2 uptake kinetics’?

A

the continued increase in oxygen uptake as time progresses, irrespective of intensity

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7
Q

what is the impact of slow component of VO2 on performance?

A

the efficiency with which the body uses oxygen is progressively lost when continuing at the same speed

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8
Q

what is VO2 drift caused by?

A
  • recruitment of less efficient fibres
  • less efficient ATP production
  • reliance on FFA oxidation
  • increased temperature
  • increase in circulating catecholamines
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9
Q

what is VO2 max?

A

the point at which oxygen consumption no longer increases with an increase in exercise intensity

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10
Q

what are the limits to VO2 max?

A

central physiological functions (pulmonary diffusion, cardiac output, blood oxygen carrying capacity)
peripheral physiological functions (muscle diffusion capacity, mitochondrial enzyme levels, capillary density)

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11
Q

which parameters can be measured to measure anaerobic contribution to exercise?

A
  • excess post-exercise oxygen contribution (EPOC)
  • lactate threshold
  • economy of efforts
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12
Q

what does EPOC measure?

A

the volume of oxygen consumed during the minutes after exercise ceases - the amount of oxygen required to resume the body to homeostasis

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13
Q

what contributes to the requirement for oxygen to restore the body to homeostasis?

A
  • replenishment of energy sources
  • reoxidation of blood
  • decrease in circulatory hormones
  • decrease in body temperature
  • decrease in ventilation and HR
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14
Q

why does an O2 deficit accrue even at low exercise intensities?

A

as soon as respiration rate increases, lactate is produced

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15
Q

what is lactate threshold?

A

the point at which blood lactate production exceeds the body’s ability to clear lactate

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16
Q

what is appropriate training for endurance?

A

1- an activity of intensity higher than a critical threshold
2- each period of activity must be of sufficient duration
3- the activity should be repeated over time on a regular basis
4- sufficient rest must occur between training

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17
Q

what does appropriate training for endurance result in?

A
  • increases in VO2 max
  • increases in the maximal O2 delivery by increasing plasma volume and maximal cardiac output
  • enhancement of O2 diffusion into muscles
  • increases in the mitochondrial content of skeletal muscle fibres
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18
Q

what are the aerobic characteristics of athletes?

A
  • high VO2 max
  • high lactate threshold
  • high economy of effort
  • high percentage of type I muscle fibres
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19
Q

what are the causes of fatigue?

A
  • inadequate energy delivery/metabolism
  • accumulation of metabolic byproducts
  • failure of muscle contractile mechanism
  • altered neural control of muscle contraction
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20
Q

what is fatigue?

A

inability to sustain muscle contractions after sustained exercise

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21
Q

by which two ways might there be inadequate energy delivery?

A
  • depletion of phosphocreatine

- depletion of glycogen and associated events

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22
Q

how is perception of fatigue related to glycogen?

A

relates to total depletion rather than rate of depletion

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23
Q

how does build up of inorganic phosphate lead to fatigue?

A

leads to a decrease in contractile force due to decreased calcium release from the SR

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24
Q

how does heat affect fatigue?

A

alters metabolic rate and enzyme activity, precooling muscles prolongs exercise

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25
Q

what is the primary cause of fatigue in maximal exercise?

A

build up of lactic acid

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26
Q

how is pH drop regulated?

A

the HCO3 buffer minimises the drop in pH from 7.1-6.5 rather than a theoretical possible 1.5

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27
Q

how does acidosis affect performance?

A

a drop in pH affects phosphofructokinase, a pH of less than 6.9 inhibits glycolytic enzymes and ATP synthesis, a pH of less than 6.4 prevents glycogen breakdown. H+ can also displace Ca from fibres, disrupting actin-myosin

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28
Q

how does fatigue cause failure of muscle contractile mechanism?

A

depletion of glycogen granules located in myofibrils interferes with excitation-contraction coupling and calcium release from the sarcoplasmic reticulum

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29
Q

how is fibre excitability related to glycogen?

A

related to presence of endogenous glycogen, not stores of glycogen

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30
Q

how can fatigue cause failure at the NMJ?

A
  • decrease in ACh synthesis and release
  • altered ACh breakdown in synapse
  • increase to muscle fibre stimulus threshold
  • altered muscle resting membrane potentials
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31
Q

why is neural transmission modulated in extreme exertion?

A

brain regulates power output from the muscles to prevent unsafe levels of exertion that may damage tissues or cause catastrophic events.

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32
Q

what environmental changes occur with increased altitude?

A
  • pO2 of the air increases
  • temperature decreases
  • boiling point of water decreases
  • pH2O increases
  • solar radiation increases
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33
Q

why is oxygen uptake impaired at altitude?

A

as PO2 of the air increases, there is a smaller diffusion gradient between alveoli and pulmonary blood

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34
Q

what are the symptoms of hypoxia?

A

headache, nausea, insomnia

35
Q

what physiological changes occur at altitude?

A
  • respiratory
  • cardiovascular
  • renal
  • metabolic
36
Q

what respiratory changes occur at altitude?

A

pulmonary diffusion remains the same, but ventilation increases, causing the concentration of CO2 in the alveoli to decrease, and movement of CO2 from blood into the lungs, this causes pH of blood to increase. the increase in blood pH causes the oxyhaemoglobin curve to shift left.

37
Q

what physiological changes are triggered by reduced PO2 at high altitude?

A

low PO2 is sensed by the carotid body, which alerts the brain. the brain sends signals to the body to increase ventilation and heart rate, and also to dilate peripheral blood vessels in the arms, legs, hands and feet

38
Q

what are the effects of high altitude on the cardiovascular system?

A
  • decrease in blood plasma volume
  • increase in haematocrit
  • altered cardiac function due to release of noradrenaline and adrenaline
39
Q

what are the renal responses to high altitude?

A
  • decrease in plasma volume due to increase in urination
  • increase in erythropoietin release from kidneys
  • excretion of HCO3
40
Q

what are the effects of high altitude on metabolism?

A
  • increase in BMR and reliance on carbohydrates
  • increase in lactic acid (transient)
  • increase in anaerobic respiration
41
Q

what is meant by ‘the lactate paradox’?

A

the initial increase in lactate is reversed as you acclimate despite no changes to VO2 max

42
Q

what are the pulmonary adaptations to altitude that occur with acclimation?

A
  • increase in ventilation
  • increase in pulmonary diffusing capacity
  • arises due to an increase in blood volume of pulmonary capillaries
43
Q

what changes to the blood occur with acclimation to altitude?

A
  • transient increase in EPO decreases after a month
  • polycythaemia (increase in RBCs)
  • return to normal plasma volume
  • increase in tissue vascularity
44
Q

what changes to muscle occur with acclimation to altitude?

A

-decrease in mass
-decrease in fibre area and capillary density
decrease in glycolytic enzyme activity
-decrease in mitochondrial function

45
Q

what are the health risks associated with high altitude?

A

acute altitude sickness
high altitude pulmonary oedema
high altitude cerebral oedema
frost-bite

46
Q

what is the heat balance equation?

A

(metabolism - work done) - (radiative heat loss + conduction heat loss + evaporation heat loss) = Storage

47
Q

by which routes does transfer of heat from core to skin occur?

A
  • passive conduction

- convection via blood (primary route)

48
Q

how does autonomic control of skin blood flow help regulate temperature?

A

when conditions are hot, vasodilation permits greater heat transfer from skin to surroundings. in cold conditions, vasoconstriction prevents heat transfer from skin to surroundings

49
Q

by which mechanisms does heat move from the skin to the environment?

A
  • radiation
  • conduction
  • convection
  • evaporation
50
Q

what are the causes of heat exhaustion?

A

body cannot dissipate the heat load due to:

  • dehydration (reduces sweating)
  • hypovolaemia (reduces blood flow from muscle to core to skin)
51
Q

where are thermal sensors located on the body?

A

on the skin surface, within the body core and at high densities in the pre-optic area and anterior hypothalamus

52
Q

what are the types of peripheral thermoreceptor?

A

warm and cold - each is anatomically distinct and innervates specific sensitive spots on the skin surface

53
Q

how do peripheral thermoreceptors bring about responses to cold?

A

low skin temperature causes firing rate of cold receptors to increase, driving shivering and thermogenesis

54
Q

what is the response to moderate heat load?

A

autonomic response primarily increases heat transfer rate from core to skin by increasing cutaneous blood flow

55
Q

how is sweating activated?

A

when heat load is high enough, the autonomic nervous system activates eccrine sweat glands

56
Q

how does sweating cool the body?

A

as sweat is secreted onto the surface of the skin, the partial pressure of water vapour is increased, promoting evaporation

57
Q

what is unusual about innervation of eccrine sweat glands?

A

although sympathetic, acetylcholine is the neurotransmitter

58
Q

what is shivering?

A

involuntary, rhythmic contractions and relaxation of skeletal muscle

59
Q

why does temperature increase in exercise?

A

at the onset of exercise, rate of heat production increases in proportion to the exercise intensity. this increases past the rate of heat dissipation

60
Q

how is temperature increase in exercise regulated?

A
  • rise in core temp is detected by hypothalamic integrator, which compares it to reference
  • detects error
  • directs neural outputs that activate heat dissipation
  • this causes skin blood flow to increase, and sweating to increase as well
61
Q

what is meant by cardiovascular drift?

A

increase in HR after 10 minutes of prolonged moderate exercise in a warm environment where cardiac output is maintained

62
Q

what are the explanations for cardiovascular drift?

A

1- as blood moves to the skin, reduced venous return, stroke vol and increase in HR
2- reduced ventricular filling time due to increased HR due to hyperthermia or dehydration

63
Q

what causes vasodilation?

A

decrease in vasoconstrictor tone due to a decrease in NA in the synaptic cleft and a decrease in binding to post-synaptic a-adrenergic receptors

and activation of sympathetic cholinergic nerves

64
Q

what are the limitations to exercise in heat?

A

cardiovascular system overload

‘critical temperature theory’

65
Q

what is meant by cardiovascular system overload?

A
  • heart cannot provide sufficient blood flow to exercising muscle and skin
  • there is impaired performance and risk of overheating
66
Q

what is meant by critical temperature theory?

A

brain shuts down exercise at 40-41 degrees - explains limitation in trained, well acclimated athletes

67
Q

how does light sweating differ from heavy sweating?

A

light sweating - slow movement through sweat duct, the sweat is more dilute due to resorption of Na and Cl
in heavy sweating, there is fast movement through the duct, and sweat is less dilute due to loss of Na and Cl

68
Q

how is sweating triggered?

A

release of ACh -> activation of GPCR -> PLC stimulated -> stimulates PKC -> release of calcium -> primary secretion

69
Q

what is stimulated by exercise and body water loss?

A

adrenal cortex and antidiuretic hormone secretion from posterior pituitary gland

70
Q

how is sweating altered by training?

A

trained people have altered sweat composition, less sodium and chloride loss compared to untrained people

71
Q

what are the effects of acclimation to exercise in the heat?

A

temporary increase in plasma volume

  • supports stroke volume to allow cardiac output to remain the same
  • greater skin blood flow
  • more widespread and dilute sweating
72
Q

which 5 factors interact to improve physiological adjustments and exercise tolerance during heat stress?

A
  • acclimation
  • training status
  • age
  • gender
  • body fat level
73
Q

how does sweating change when acclimatised to exercise in heat?

A
  • lowered threshold for start of sweating
  • more effect distribution of sweat over skin surface
  • increased sweat output
  • lowered salt concentrations of sweat

these effects all work to maximise cooling via evaporation, and to preserve electrolytes in extracellular fluid

74
Q

list the health risks associated with exercise in heat

A
  • heat cramps
  • heat exhaustion
  • heat stroke
75
Q

what differences are there between the sexes in terms of response to exercise in heat?

A

women have lower sweat rates but higher numbers of active sweat glands
-advantage in humid climates, but a disadvantage in hot, dry climates

76
Q

when does non-shivering thermogenesis occur?

A

when peripheral vasconstriction is not adequate to prevent heat loss

77
Q

how is non-shivering thermogenesis regulated?

A

by the hypothalamus, based predominantly on the calorigenic action of noradrenaline released from sympathetic nerve endings. localised to skeletal muscles and brown adipose tissue

78
Q

when does cold habituation occur and what are the effects?

A

after repeated cold exposures without significant heat loss. the effects are vasoconstriction and reduced shivering

79
Q

what are the effects of acclimation to cold on metabolism?

A

enhanced metabolic rate, heat production due to shivering

80
Q

what is insulative acclimation and when does it occur?

A

enhanced skin vasoconstriction, causing increase in peripheral tissue insulation. occurs when metabolic rate cannot prevent heat loss

81
Q

how does body composition affect heat loss?

A
  • higher inactive peripheral muscle - increased insulation
  • high subcutaneous fat - increased insulation
  • decreased surface area:mass ratio - decreased heat loss
82
Q

why is heat loss faster in water than in cold air?

A

water has a thermal conductivity that is 26 times greater than air

83
Q

how does body temperature respond to cold water/

A

body temp will remain constant until water temp is lower than 32 degrees
core temp will decrease by 2.1 degrees per hour in 15 degree water

84
Q

what are the physiological responses to exercise in the cold?

A
  • decreased muscle function
  • reduced production of metabolic heat when fatigued
  • no increase in FFA oxidation upon secretion of catecholamines
  • increase in muscle glycogen utilisation

exercise physiology and pharmacology (11 decks)

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