Limits to endurance exercise

Question 1

What is fatigue (in an exercise context)?

Answer 1

an inability to maintain power output or force during repeated muscle contractions

Question 2

Performance velocity or power = ?

-Joyner & Coyle (2008)

Answer 2

(performance VO2 + performance O2 deficit) X gross mechanical efficiency

Question 3

What main factors influence performance VO2?

Answer 3

> lactate threshold

>maximal oxygen consumption

Question 4

What 5 factors influence maximal oxygen consumption?

Answer 4

1. muscle capillary density
2. stroke volume
3. max HR
4. hemoglobin content
5. aerobic enzyme activity

Question 5

What is the average VO2 max of an untrained male?

Answer 5

~ 40 ml per kg per minute

Question 6

What is the ‘upper human limit’ for VO2 max?

Answer 6

93-95 ml per kg per minute observed in Norwegian cross country skier Bjorn Daehlie

Question 7

Does VO2 max correlate with performance parameters?

Answer 7

Yes,
+vely correlates with average marathon race speed and -vely correlates with 5k time
- (Maughan, 1990)

Question 8

VO2 max is a predictor of…?

Answer 8

Potential

Question 9

In the average person, are lungs the limiting factor in maximal O2 uptake?

Answer 9

Not usually no, as lung capacity is larger than required.

Of greater issue for women (smaller lung capacity) and the highly trained.

Question 10

What is exercise-induced arterial hypoxaemia (EIAH)?

Answer 10

low arterial oxygen saturation

Question 11

What may cause EIAH in a situation where there is low alveolar ventilation?

Answer 11

> a reduced drive to breath

> a mechanical limitation to breathing

Question 12

What may cause EIAH in a situation where there is adequate alveolar ventilation?

Answer 12

> a low ventilation : perfusion
diffusion limitations
- pulmonary oedema
- transit time issues

Question 13

Does exercise fatigue the respiratory muscles?

Provide evidence for your answer

Answer 13

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)

Question 14

Could reducing the load placed on respiratory muscles improve endurance performance?

Answer 14

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

Question 15

Is muscle blood flow a limiter in maximal oxygen consumption?

Answer 15

probs not unless respiratory effort is sky high

Question 16

What influence does cardiac output have on maximal oxygen consumption?

Answer 16

a good linear relationship has been observed between maximal cardiac output (mainly influenced by stroke volume) and maximal oxygen consumption
- (Liguzunski & Korzeniewski, 2007)

Question 17

What influences performance other than the aerobic and anaerobic capabilities of the body?

Answer 17

Gross mechanical efficiency

two individuals of equal VO2 max can have different performances due to differences in economy.

Question 18

Describe the Paula Radcliffe anecdote that supports the influence of mechanical efficiency on performance

Answer 18

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)

Question 19

What happens to the contribution of muscle glycogen as a fuel source as exercise intensity increases?

Answer 19

increases

Question 20

Is my carb-loading before a race good science, or do I just have terrible impulse control?

Answer 20

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)

Question 21

Which of glycogen, glucose or fatty acids has the highest relative rate of ATP resynthesis?

Answer 21

glycogen > glucose > fatty acids

Question 22

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?

Answer 22

Carbs are more O2 efficient than fats.

More energy derived per L of O2 from carbs than fats.

Question 23

What is the likely fatiguing mechanism during activity <120 s?

Answer 23

excitation-contraction coupling failure

Question 24

What is the likely fatiguing mechanism during activity up to 30-45 minutes?

Answer 24

accumulation of fatiguing metabolites and/or oxygen dificit

Question 25

What is the likely fatiguing mechanism during activity up to 3-4 hours?

Answer 25

glycogen depletion

Question 26

What is the likely fatiguing mechanism during activity longer than 4 hours?

Answer 26

central fatigue, muscle damage (running)

Question 27

How does blocking pain receptors/perception influence performance?

Answer 27

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)

Question 28

What is the biggest influencer on maximal oxygen uptake?

Answer 28

Cardiac output (via stroke volume)

explains intra-individual differences as well

Question 29

Explain the phrase

“VO2 max is a measure of potential”

Answer 29

the proportion of VO2 max that is sustainable and efficiency will then determine performance speed/power

Question 30

What is Fick’s equation?

Answer 30

VO2 = Q(a-vO2 diff)

Question 31

What is a-vO2 diff?

Answer 31

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.

Question 32

Is a high a-vO2 diff conducive to better performance, or a low a-vO2 diff?

Answer 32

high