Exercise Flashcards
What is maximal oxygen uptake (VO2max) and how is it measured?
The highest rate of oxygen consumption that can be achieved during maximal exercise
Measured using a graded exercise test
What is the primary limiting factor in determining VO2max in a healthy person?
Cardiac output
Normal skeletal muscle can utilize more oxygen than can be delivered by the CV system
What factors affect VO2max?
Genetics - 25-50% variance
Fitness level - can increase it 15-20%
Age - declines with age after 18
Gender - less in females
Body mass
How does minute ventilation change in response to steadily increasing levels of exercise?
Increases linearly until about 2/3s of the way through a maximum exercise effort where it hits the ventilatory threshold
At this point, there is a disproportionate increase in Ve to the exercise intensity
How does PaCO2 change in response to steadily increasing levels of exercise?
Remains relatively constant until the venilatory threshold is reached
At this point lactate levels rise, causing a drop in pH, therefore stimulating an increase in minute ventilation and a subsequent drop in PaCO2
How does arterial pH change in response to steadily increasing levels of exercise?
Remains constant until the ventilatory threshold is reached
At this point the pH starts to fall because the increase in Ve cannot fully compensate for the developing metabolic acidosis
How does PaO2 change in response to steadily increasing levels of exercise?
Remains relatively constant throughout exercise
What mediates the early and delayed responses of the CV system to exercise?
Early responses - a central command center activated botht he motor cortex and CV centers in parallel
Delayed responses - Mediated by mechanical and chemical signals arising from contracting skeletal muscles and CV reflexes
What is the result of autonomic nervous system activation during dynamic exercise?
Hypothalamus activation results in a decrease in parasympathetic activity and an increase in sympathetic activity
Afferent signals from mechanoreceptors and chemoreceptors
Central command feed-forward mechanisms
What mechanical mechanisms are involved in the response to dynamic exercise?
Muscle pump activity - increase blood flow to the heart, leading to increased CO
Respiratory activity - Increasing the depth and rate of respiration enhances the flow to blood to the heart
What metabolic mechanisms are involved in the response to dynamic exercise?
Muscles release vasodilator metabolites to increase blood flow to contracting muscles
What is the effect of epinephrine release during exercise?
Enhances the effects of sympathetic stimulation
Also mobilizes glucose from the liver and fatty acids from adipose tissue
How does heart rate increase in response to exercise?
Increases in direct proportion to exercise intensity due to initial decrease in vagal tone, followed by sympathetic stimulation
Maximal HR decreases as a function of age
How does stroke volume change in response to exercise?
Increases at first, but the plateaus as the level of exercise becomes more intense
Maintained by mechanisms that aid in venous return and ventricular filling
May decline at very high levels of activity
How does systemic vascular resistance change in response to exercise?
Decreases as work intensity increases because of vasodilation in the actively contracting muscles
