Limits to endurance exercise Flashcards
What is fatigue (in an exercise context)?
an inability to maintain power output or force during repeated muscle contractions
Performance velocity or power = ?
-Joyner & Coyle (2008)
(performance VO2 + performance O2 deficit) X gross mechanical efficiency
What main factors influence performance VO2?
> lactate threshold
>maximal oxygen consumption
What 5 factors influence maximal oxygen consumption?
- muscle capillary density
- stroke volume
- max HR
- hemoglobin content
- aerobic enzyme activity
What is the average VO2 max of an untrained male?
~ 40 ml per kg per minute
What is the ‘upper human limit’ for VO2 max?
93-95 ml per kg per minute observed in Norwegian cross country skier Bjorn Daehlie
Does VO2 max correlate with performance parameters?
Yes,
+vely correlates with average marathon race speed and -vely correlates with 5k time
- (Maughan, 1990)
VO2 max is a predictor of…?
Potential
In the average person, are lungs the limiting factor in maximal O2 uptake?
Not usually no, as lung capacity is larger than required.
Of greater issue for women (smaller lung capacity) and the highly trained.
What is exercise-induced arterial hypoxaemia (EIAH)?
low arterial oxygen saturation
What may cause EIAH in a situation where there is low alveolar ventilation?
> a reduced drive to breath
> a mechanical limitation to breathing
What may cause EIAH in a situation where there is adequate alveolar ventilation?
> a low ventilation : perfusion
diffusion limitations
- pulmonary oedema
- transit time issues
Does exercise fatigue the respiratory muscles?
Provide evidence for your answer
Maximum inspiratory pressure drops 16.5% post marathon
- (Loke et al, 1982)
Diaphragm fatigues when exercise intensity rises above 80% VO2 max, NOT during voluntary hyperventilation though.
- (Johnson et al, 1996)
Could reducing the load placed on respiratory muscles improve endurance performance?
You better your socks it could.
Unloaded breathing during a cycling test @90% VO2 max…
> increased time to fatigue
> lowered leg RPE
> lowered VO2 at 5 minutes
when compared to loaded breathing and a control group.
All participants were trained cyclists with VO2 max of >63 ml per kg per minute
Is muscle blood flow a limiter in maximal oxygen consumption?
probs not unless respiratory effort is sky high
What influence does cardiac output have on maximal oxygen consumption?
a good linear relationship has been observed between maximal cardiac output (mainly influenced by stroke volume) and maximal oxygen consumption
- (Liguzunski & Korzeniewski, 2007)
What influences performance other than the aerobic and anaerobic capabilities of the body?
Gross mechanical efficiency
two individuals of equal VO2 max can have different performances due to differences in economy.
Describe the Paula Radcliffe anecdote that supports the influence of mechanical efficiency on performance
from 1991-95, Paula reduced her 3k time despite a poorer VO2 max, in part due to improved running efficiency and a raised lactate threshold.
- (Jones, 1998)
What happens to the contribution of muscle glycogen as a fuel source as exercise intensity increases?
increases
Is my carb-loading before a race good science, or do I just have terrible impulse control?
Both,
a higher carbohydrate meal prior to endurance exercise was linked with a longer time to fatigue during endurance tests as far back as 1967
- (Bergstrom et al, 1967)
Which of glycogen, glucose or fatty acids has the highest relative rate of ATP resynthesis?
glycogen > glucose > fatty acids
All the way back in 1920, these two utter lads, Krogh and Lindhard, made their own old-timey douglas bag and set about trying to find out how oxygen efficient carbs and fats were.
Can you tell me what they found?
Carbs are more O2 efficient than fats.
More energy derived per L of O2 from carbs than fats.
What is the likely fatiguing mechanism during activity <120 s?
excitation-contraction coupling failure
What is the likely fatiguing mechanism during activity up to 30-45 minutes?
accumulation of fatiguing metabolites and/or oxygen dificit
What is the likely fatiguing mechanism during activity up to 3-4 hours?
glycogen depletion
What is the likely fatiguing mechanism during activity longer than 4 hours?
central fatigue, muscle damage (running)
How does blocking pain receptors/perception influence performance?
improved cycling power output over the short-term (first 2 km), however, performance dropped below that of control group after the first 2 km, resulting in no differences in performance over the whole 5 km trial.
- Amann (2009)
What is the biggest influencer on maximal oxygen uptake?
Cardiac output (via stroke volume)
explains intra-individual differences as well
Explain the phrase
“VO2 max is a measure of potential”
the proportion of VO2 max that is sustainable and efficiency will then determine performance speed/power
What is Fick’s equation?
VO2 = Q(a-vO2 diff)
What is a-vO2 diff?
arteriovenous oxygen difference
the difference in oxygen content of the arterial and venous blood vessels.
gives an indication of how much O2 has been removed from the blood in the capillaries.
Is a high a-vO2 diff conducive to better performance, or a low a-vO2 diff?
high
