Week 1 - Exercise physiology Flashcards
What is ATP and how does it function?
The ‘currency’ of a muscle.
Actin-myosin cross-bridge cycling
- ATP-energised myosin head attaches to the exposed actin binding site
- Power-stroke occurs as one Phosphate ion dissociates (ATP→ ATP + Pi)
- ADP dissociates from cross-bridge but actin-myosin link remains intact
- New ATP releases the myosin head from actin site + cycle starts again
Key things about ATP?
→ ATP is an essential part of muscle contraction
→ Continued muscle contraction requires a continual supply of ATP
What are the methods of ATP synthesis?
Phosphocreatine
Anaerobic glycolysis
How does phosphocreatine synthesise ATP?
→ Stored locally in the muscle
→ Very fast + powerful but short-lived system
→ Initial 2-10s of exercise
Creatine stimulates oxidative phosphorylation + PC is resynthesised using mitochondrial ATP during rest + recovery.
How does anaerobic glycolysis synthesise ATP?
→ Dehydration of glucose into pyruvate
→ Quite fast + powerful, 10s-2mins
→ During onset of exercise or high intensity exercise, pyruvate is converted to lactate (anaerobic pathway)
How does aerobic ATP synthesis occur (oxidative phosphorylation)?
- Occurs exclusively in the mitochondria
- Can metabolise carbohydrates, lipids or proteins
- Primary energy source during sustained, moderate activity
- Oxygen is the final electron acceptor in the electron transport chain
- Most efficient + sustainable system
- Slowest system
- Reliant on oxygen delivery to cells
What energy supplies are used at different stages of exercise?
ATP-PCr → first 10s of exercise, very rapid reduction, rapidly used up e.g. sprint
Anaerobic glycolytic → peaks @ 20s of exercise, slowly decreases
Aerobic (oxidative phosphorylation) → takes longer to get going (60s), at this point oxidative mechanisms take over, in steady sustained exercise - main system for ATP synthesis.
Oxygen uptake
Oxygen being taken up and used by muscle cells
How does oxygen uptake change in steady-state exercise?
from rest e.g. sitting in chair
Oxygen uptake gradually increases until it meets the demand of the work rate.
What is a cardio-pulmonary exercise test? (CPET)
Incremental ramp test
How does oxygen uptake change in incremental exercise from rest?
O2 uptake is parallel to workload until plateau
Plateau = VO2 max
CO2 starts to increase at faster rate than work rate after certain point - shows anaerobic systems have been implemented e.g. anaerobic glycolysis → get extra ATP to meet demand
Oxygen deficit + debt?
O2 deficit repayed during recovery period
→ Recovery depends on fitness + level of exercise/level of exertion
→Period of time taken for O2 uptake to increase to meet demand of person - creates lag - when exercise starts O2 takes longer to reach demand
Co-ordination of what is required to meet the demands of exercise?
Interactions between mitochondria, muscle, cardiovascular and respiratory systems
Factors influencing oxygen delivery?
DO2 - O2 delivery
VO2 - O2 uptake
What is VO2 max?
Maximum rate of oxygen your body is able to use during exercise.
What is DO2?
O2 delivery
= Arterial oxygen content X Cardiac output
Arterial oxygen content?
Oxygen bound to haemoglobin + oxygen dissolved in plasma
Cardiac output?
Heart rate X Stroke volume
What is VO2?
O2 uptake
= (CaO2 - CvO2) x (SV x HR)
What is SV x HR
Cardiac output
What is CaO2 - CvO2
Difference between venous O2 content + arterial O2 content
What is CaO2 - CvO2 influenced by?
→ Muscle blood flow
→ Capillary density
→ Mitochondrial density
→ Hb-O2 affinity (Bohr effect)
→ Muscle mass
→ Muscle fibre type
→ Nutrition (substrate) availability
What are the different systems that have a response to exercise?
- respiratory
- cardiovascular
- coronary circulation
- peripheral circulation
Respiratory response to exercise?
→ Minute Ventilation increases:
- 8L/min at rest
- >200ml during exercise
→ Depth of breath increases before the rate of breath
Respiratory muscle uses:
- 2% of total VO2 at rest
- 11% of total VO2 during exercise
- Up to 50% of VO2 during exercise in the obese
Why does depth of breathing increase before the rate of breath?
Due to afferent feedback from proprioceptors in exercising joints/muscles.
Key points about respiratory response to exercise?
→ Ventilatory reserve exists beyond the observed ventilation during maximal exercise in healthy individuals
→ Most of the response comes from muscle/joint proprioceptors
→ Arterial PCO2 + PH remain relatively constant during most exercise intensities - means minimal role for chemoreceptors
→ Anticipatory response increases breathing rate + depth before exercise
Cardiovasular response to exercise?
→ CO (HR x SV) - increases up to 5x during exercise (5L/min to 25L/min)
→ HR increases linearly with work rate up to 3X
→ SV increases rapidly at first then plateaus <2x
→ Cardiac output is the limiting factor to oxygen delivery in the healthy individual
What is stroke volume?
The amount of blood pumped out of the left ventricle during each systolic cardiac contraction
Why is cardiac output the limiting factor to O2 delivery?
Most people have cardiac limitation to their maximal exercise tolerance.
Blood is not pumped out to the muscles fast enough to supply oxygen to the working muscles during exercise.
Coronary circulation response to exercise during exercise? (not maximal)
→ Coronary arteries receive blood during diastole
→ During exercise:
- increased flow to coronary vessels (due to increased cardiac output)
- vasodilation of coronary vessels
- reduced duration of diastole with increased HR
Coronary circulation response during maximal exercise?
- 6x increase in oxygen demand from the left ventricle
- 5x increase in coronary circulation
Peripheral circulation response to exercise?
→ Blood flow is redistributed from non-vital organs to the muscles e.g. digestive tract - 25% of VO2 @ rest, falls to 5% during vigorous exercise.
→ Blood flow to the skin increases for heat dissipation
→ Arterioles vasodilate - up to 25x increased blood flow
→ Mean arterial pressure (BP) remains fairly constant
Why does blood pressure remain fairly constant during exercise?
Mean arterial pressure = CO x Total peripheral resistance
Mean arterial pressure means a combination of systolic + diastolic BP figures.
During exercise cardiac output increases and arterioles vasodilate which decreases the total peripheral resistance which is why BP remains mostly
Physiological responses to endurance training at rest?
Stroke volume → increase
Heart rate → decrease
Cardiac output → same
a-vO2 →same
Systolic blood pressure → decrease
Diastolic blood pressure → same
Blood volume → increase
Capillary density → increase
Mitochondrial density → increase
What does mitchondiral density do?
makes O2 uptake more efficient
What is minute ventilation?
respiratory rate x tidal volume
Physiological responses to endurance training at submaximal exercise?
Same as rest apart from:
→ increased a-vO2 difference
→ decreased diastolic blood pressure
Physiological responses to endurance training at maximal exercise?
Stroke volume → increase
Heart rate → decrease or stay the same
Cardiac output → increase
a-VO2 difference → increase
VO2 → increase
Systolic BP → stay same
Diastolic BP → decrease
Blood volume → increase
Capillary density → increase
Mitochondrial density → increase
Physiological responses to High Intensity Interval Training (HIIT)
Increase in:
→ VO2 peak
→ High density lipoproteins
→ Adiponectin, insulin sensitivity and b cell function
→ PGC
→ Maximal rate of Ca2+ uptake
→ Availability of nitric oxide
→ Cardiac function
→ Enjoyment of excercise
→ Quality of life
Decrease in:
→ Systolic + diastolic blood pressure
→ Triglycerides and fasting glucose
→ Oxidative stress and inflammation
→ FATP-1 and FAS
Brief summary of exercise physiology?
- Exercise demands oxygen and a substrate are increase
- Chemical, mechanical and thermal stimuli affect alterations in function
→ The body firstly uses immediately energy sources that include ATP
→ Alternatively, utilisation of the Adenylate Kinase Reaction as well as the Phosphocreatine system are important
→ Resynthesis of ATP from energy-dense substrates via Glycolysis and fat metabolism
