Limits to Endurance Exercise

Question 1

Define fatigue in the context of exercise

Answer 1

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

Question 2

What is the difference between exercise performance and exercise capacity?

Answer 2

Endurance performace: time trials, VO2max

Endurance capacity: time to exhaustion

Question 3

According to Joyner and Coyle 2008, What determines performance velocity/power?

Answer 3

(Performance VO2 (aerobic) + Performance O2 deficit (anaerobic)) * Gross mechanical efficiency

Question 4

What determines Performance VO2 (aerobic) in the Joyner and Coyle 2008 model of Performance Velocity/Power?

Answer 4

Lactate Threshold and Maximal Oxygen Consumption

Question 5

What are the morphological components of Lactate Threshold and Maximal Oxygen Consumption?

Answer 5

Muscle Capillary Density
Stroke Volume
Max HR
Hemoglobin content
Aerobic Enzyme Activity

Question 6

What are the morphological components/determinants of Gross Mechanical Efficiency according to the Joyner and Coyle 2008 model of Performance Velocity/Power?

Answer 6

• Anthropometry and Elasticity

- % Slow Twitch (Type I) Muscle Fibres

Question 7

What does Maughan 1990 say about endurance performance?

Answer 7

There is a positive linear relationship between average racing speed/5km race time and VO2max

Question 8

What is the Fick equation for VO2max?

Answer 8

VO2 = Q (a-v O2 diff)

Q = Cardiac Output
a-vO2diff = Artery/Vein oxygen difference

Question 9

How is Muscle VO2 measured?

Answer 9

• Tracer infused into the ante-cubital vein
• Blood sampled from Femoral Artery and Femoral Vein (And Subclavian vein)
• Saline infusion to femoral vein and subclavian vein

Question 10

What are the key limiting steps in O2 transport?

Answer 10

• Lungs
• Heart
• Muscles
• Mitochondria

Question 11

Do lungs typically limit exercise?

Answer 11

Not typically. Ventilation increases more than VO2. Alveolar PO2 is maintained at maximal exercise

Question 12

What has Powers et al 1989 found about the potential for the lungs to be a limiting factor for endurance performance?

Answer 12

• Normoxia vs Hyperoxia
• Normal group no difference in VO2max
• Highly trained group significantly higher VO2max in hyperoxia

Question 13

In what two ways can a ventilation-perfusion mismatch

cause exercise induced arterial hypoxemia?

Answer 13

• If cardiac output low, then increasing ventilation further won’t increase oxygen uptake
• If ventilation rate too low, then the max amount of oxygen that could be taken up is not achieved

Question 14

How can Pulmonary Oedema limit endurance performance?

Answer 14

Swelling of the interstitial fluid between capillary endothelium and alveolar epithelium increases gas diffusion distance, slowing the rate of exchange

Question 15

What evidence exists to suggest that respiratory muscles limit endurance performance?

Answer 15

Harms et al 2000 found that time to fatigue at VO2max was higher when air was mechanically forced into the lungs compared to breathing through an altitude mask, or breathing normally

Question 16

How is maximum inspiratory mouth pressure affected by exercise?

Answer 16

• 18% decrease following 20km cycling time trial (Romer et al 2002)
• 11% decrease following 6 min rowing time trial (Volianitis et al 2001)

Question 17

How is the diaphragm affected by exercise?

Answer 17

Diaphragm fatigues during exercise above 80%VO2max, (but not voluntary hyperventilation) (Johnson et al 1996)

Question 18

In summary, what is the respiratory muscle metaboreflex?

Answer 18

When the respiratory muscles fatigue, their blood flow needs increase, reducing the available blood flow to the legs, reducing performance

Question 19

Does cardiac output limit endurance performance?

Answer 19

Yes. Linear relationship between cardiac output and VO2max (Liguzinski and Kozeniewski 2007)

Question 20

Can muscle fuel be a limiting factor to endurance performance?

Answer 20

Yes. A majority of fuel at 75%+ Wmax exercise intensity is muscle glycogen. If not enough glycogenthat will reduce your performance.

Question 21

Who established a positive linear relationship between Amount of Carbs in Diet, Muscle Glycogen and Time to fatigue?

Answer 21

Bergstrom et al 1967