38. Exercise physiology Flashcards
What are the two types of exercise and how does muscle usage differ accordingly?
Dynamic exercise - rhythmical movements of joints and contraction and relaxation of muscles e.g. swimming, running and cycling
Static exercise - maintained contraction for a length of time e.g. lifting
What are the sources of energy for skeletal muscle function?
Immediate - creatine phosphate/phosphocreatine (no o2)
Non-oxidative - anaerobic glycolysis
Oxidative - aerobic/oxidative metabolism
Describe the immediate source of energy for skeletal muscles
Creatine phosphate - high concentrations of this in the muscle
This provides a high storage of high-potential phosphate to maintain contraction
Catalysed by creatine kinase
Describe anaerobic glycolysis and the consequences of this
Excess pyruvate is converted to lactate
There is a lactic acid build up
So there is a drop in the pH and the muscle begins to fatigue
What is ‘VO2’?
This is the volume of oxygen that is consumed during oxidative metabolsim
What is ‘VO2 max’?
This is the highest peak oxygen uptake that an individual can obtain during dynamic exercise (whilst using large muscle groups during a few minutes under normal conditions at sea level)
This is reached when the oxygen consumption remains at a steady state despite an increase in workload
What is the significance of VO2 max?
VO2 max reflects the aerobic physical fitness of the individual
Is an important determinant of their endurance capacity during prolonged, sub-maximal exercise
What is the anaerobic threshold?
(aka. the lactate threshold)
This is where further increases in work are not accompanied by oxygen uptake - the blood lactate rises steeply
SO the anaerobic threshold is the point where lactate begins to accumulate in the bloodstream
Varies from person to person
How can the anaerobic threshold be improved?
Untrained individuals have a low AT whilst elite endurance athletes have a high AT
What is the aim of the cardiovascular system during exercise?
Aim is to increase oxygen delivery to the skeletal and cardiac muscle
What are the main responses of the CVS during exercise?
- Rise in cardiac output via an increase in SV and HR
2. Redistribution of larger proportion of CO to the active muscles
How is the heart rate increased by the CVS?
Generally, HR is kept low by the vagus nerve (parasympathetic) so during exercise, there is a reduced activity of parasympathetic and increased activity of sympathetic nerves
Sympathetic nerves also act to cause partial vasoconstriction of blood vessels
Together this results in an increased HR and mobilisation of blood from the great veins
How is the stroke volume increased by the CVS?
Increased venous return
Increased end diastolic volume (and hence increased preload)
According to Starling’s law, this increases the SV
Sympathetic activity has a positive inotropic response on the heart (increased force of contractility)
What is the main component that can increase the cardiac output?
Mainly due to an increased heart rate - the stroke volume reaches maximum levels at a fairly moderate exercise intensity
What is ‘heart remodelling’?
This is a long term response of the heart to increased levels of exercise (physiological cause) pr can be due to a disease (pathological cause)
Heart adapts to sustained increases in BP by increasing muscle mass via hypertrophy (increased cardiac myocyte size)
Why do athletes tend to have Bradycardia?
Due to the volume induced cardiac hypertrophy, the resting end diastolic volume and stroke volume is increased
SO to maintain the CO, the HR is reduced
SO athletes typically have a slower resting HR when compared to untrained individuals
By how much does blood flow to the muscles increase during exercise?
During rest, about 2-25% of the CO is to the muscles
During maximal exercise, about 90% of the increased CO is to the muscles
What are the two mechanisms that control the redistribution of flow during exercise?
- Systemic regulation
2. Local control
Describe systemic regulation of redistribution of blood flow
Mechanism to control redistribution of blood flow during exercise
Involves adrenergic receptors (adrenoreceptors) which respond to the increased sympathetic outflow
Alpha adrenoreceptors constrict the vessels in the gut and cause vasoconstriction of veins
Beta 1 adrenoreceptors (in the heart) act to increase the rate and force of myocardial contraction
Beta 2 receptors act to relax the muscle and increase the ventilation and oxygen uptake and cause vasodilation of blood (especially towards skeletal muscle)
Describe local control of redistribution of blood flow
Local regulatory factors strongly determine blood flow:
Endothelial factors - such as NO that act to relax smooth muscle and cause dilation of blood vessels
Tissue factors - adenosine, inorganic phosphates, CO2, H+, K+ that are released from contracting muscles
How does the mean arterial blood blood pressure change during exercise?
Although the total peripheral resistance decreases during exercise, the mean arterial blood pressure is raised only slightly
This is because the decreases in TPR are offset by increases in CO
How does the systolic and diastolic blood pressure change during exercise?
Systolic blood pressure increases due to the increased force of ventricular contraction
The diastolic pressure remains relatively stable or can even decrease slightly
What is the aim of the respiratory system during exercise?
To meet the body’s increased oxygen requirements via increased pulmonary minute ventilation and oxygen extraction in tissues
To what extent does ventilation increase during exercise?
Ventilation at rest is about 8l/minute but during heavy exercise, can increase to 100l/minute or more
At moderate work rates, the steady state ventilation is directly proportional to the work done (measured via oxygen uptake)
During severe exercise, the increase in ventilation is disproportionately large in relating to oxygen uptake
How is ventilation increased?
Via an increased respiratory rate and increased tidal volume
How can increased levels of oxygen be delivered to the tissues during exercise?
This is facilitated via a decrease in the Hb-O2 binding affinity during exercise
What is meant by ‘(Excess) post-exercise oxygen consumption’ (EPOC)
Essentially, as the body starts exercising, the oxygen uptake does not immediately rise to meet the demand and instead there is a delay.
SO there is an oxygen deficit before the oxygen demand is met
SO once exercise stops, the level of the oxygen being taken up is greater than the demand of the body pos-exercise
This is believed to be due to take up the oxygen that was required during the initial oxygen deficit
What are the neurological factors involved in the metabolic changes during exercise?
Not completely sure yet but believed to be: Baroreceptor reflex sensitivity Metaboreceptors Premotor area of the cerebral cortex Peripheral chemoreceptors
