Limits to exercise tolerance 2 Flashcards
Arguments against lungs being a limiting factor in VO2max?
Alveolar area is v large, ventilation increases more than oxygen uptake, pp of oxygen in alveoli and arteries is maintained at VO2max
Arguments in favour of lungs being a limiting factor in VO2max?
At normoxia, the oxygen saturation of haemoglobin declines as the intensity of exercise does, hypoventilation, mechanical constraints
What is hyperoxia?
Atmospheric oxygen partial pressure is higher than usual
What is normoxia?
Atmospheric oxygen partial pressure is the same as usual
What is hypoxia?
Atmospheric oxygen partial pressure is lower than usual
What is hypoventilation?
breathing that is too shallow
How can hypoventilation be a limitation of VO2max?
Someone may have the capacity for a certain oxygen uptake but arent sensitive enough to the stimuli (exercise) to increase the ventilation rate
What are the axis of a flow volume loop?
Flow rate in L/s on Y axis, volume in L on the x axis
How to create a flow volume loop?
Maximal inspiration then forcefully expire all air in lungs as quickly and as hard as possible
How can we test whether lung function is a limiting factor of VO2?
Changing density of inspired air
What was observed as a result of changing the density of inspired air to see whether lungs are limiting or not?
Less dense air overcomes the limitation of lungs reaching expiring capacity
What is pulmonary oedema?
Swelling in the lungs
How does pulmonary oedema negatively affect gas exchange in the lungs?
The swelling causes the interstitial space between the alveoli and capillary to increase thus gas exchange takes longer
How can alveolar capillary diffusion limit VO2max?
Only one RBC can pass through a capillary at a time. In untrained this is 0.4-0.5s whereas in trained it is <0.4. Longer means more time to take oxygen to blood so lower VO2max
Are lungs a limiting VO2max factor in untrained individuals?
Not a huge amount of evidence to support it
Are lungs a limiting VO2max factor in trained individuals?
Some evidence that this may be true
What is hyperpnea?
Increased ventilation
What is the cost of exercise hyperpnea?
Respiratory muscles have a power output of around 50 watts
WHat is unique about respiratory muscles?
They can produce a lot of force relative to their size
What is proportional assisted ventlation?
Participant begins inhaling–> rest of air is forced into lungs via machine
What is RPE?
Rating of perceived exertion
What happens to leg RPE in unloaded (proportional assisted ventilation) condition?
It is a lot lower than load or control
How to load inhalation?
Have the participant lift a small weight when they breathe in–> lungs and respiratory muscles have to work harder
What is an MIP?
Maximum inspiratory mouth pressure test
What does a MIP do?
Measures the pressure someone can generate at their mouth when they breathe in
What happens to MIP following exercise?
It decreases
Issue with doing an MIP after endurance exercise?
Athletes may be tired and so might not inspire as hard as they can
What is a volitional measure?
Relating to someones will
How is the diaphragm isolated when measuring its exertion?
Using a nasoesophageal catheter
How does a nasoesophageal catheter work work?
It goes up the nose, down the throat and into the stomach where there is two pressure transducers, one in the stomach and one in the oesophagus. WHen diaphragm contracts it moves down which increases stomach pressure and decreases esophageal pressure
What is the respiratory metaboreflex?
When respiratory muscles become fatigued, it sends a signal that changes blood flow to other muscles
What is observed regarding leg blood flow when work of breathing is increased?
It decreases
When using a nasoesophageal catheter, where are the pressure transducers?
Stomach and oesophagus
What is observed regarding leg VO2 when work of breathing is increased?
It decreases
How efficient is muscle O2 extraction?
Very
Why is muscle oxygen extraction unlikely to limit VO2max?
At high intensity exercise the difference in oxygen conc between the artery entering the muscle and the vein leaving the muscle is high meaning it is very efficient
What explains most of the variance in VO2max between people?
Cardiac output
What explains the early increase in VO2max with exercise training?
Plasma volume
What is observed in the blood in the first week after beginning training?
Rapid increase in plasma volume
How to artificially increase plasma volume?
Dextran infusion
What is observed in the VO2max of people who have had their blood plasma volume artificially increased as a result of a dextran infusion?
An increase of ~4%
How does dehydration affect performance?
It leads to a lower plasma volume which leads to lower blood flow and stroke volume
In most people, what is the correlation between VO2max and performance time in a a marathon?
High
In elite athletes, what is the correlation between VO2max and performance?
Not as strong as in the general population
Why may the VO2max of elite athletes not perfectly correlate to performance?
other factors such as mechanical efficiency, running economy etc
Which test could be better than VO2max for elite athetes?
Lactate threshold
What was observed regarding time to fatigue differences at 70%VO2max in low, mixed and high CHO diets?
The low CHO diet performed the worst with around 1 hr, the high performed the best between 2 and 5 hrs
Correlation between CHO content in diet and muscle glycogen levels?
Higher CHO content in diet means a higher muscle glycogen content
What was observed when looking at the time when muscle glycogen depletion occurs in placebo and CHO-fed groups during exercise?
They reach muscle glycogen depletion at the same time (3hrs)
Why could CHO-fed people exercise for longer than placebo despite reaching muscle glycogen depletion at the same time?
Taking on more CHO means it no longer becomes a reason for fatigue
What role can muscle glycogen have other than a fuel?
A signalling molecule
Subsarcolemmal region meaning?
Below the sarcolema
Which type of muscle glycogen storage is most closely associated with fatigue?
Intramyofibrillar
How does a lack of muscle glycogen affect calcium?
It affects its release rate
Which out of glycogen, glucose, FAs can generate ATP the fastest?
Glycogen
What is McArdles disease?
Lack of enzymes required to break down muscle glycogen
Which fuel is more efficient, carbs or fats?
Carbs
