Limits to Endurance Exercise Flashcards
Define fatigue in the context of exercise
The inability to maintain power output or force during repeated muscle contractions
What is the difference between exercise performance and exercise capacity?
Endurance performace: time trials, VO2max
Endurance capacity: time to exhaustion
According to Joyner and Coyle 2008, What determines performance velocity/power?
(Performance VO2 (aerobic) + Performance O2 deficit (anaerobic)) * Gross mechanical efficiency
What determines Performance VO2 (aerobic) in the Joyner and Coyle 2008 model of Performance Velocity/Power?
Lactate Threshold and Maximal Oxygen Consumption
What are the morphological components of Lactate Threshold and Maximal Oxygen Consumption?
Muscle Capillary Density Stroke Volume Max HR Hemoglobin content Aerobic Enzyme Activity
What are the morphological components/determinants of Gross Mechanical Efficiency according to the Joyner and Coyle 2008 model of Performance Velocity/Power?
- Anthropometry and Elasticity
- % Slow Twitch (Type I) Muscle Fibres
What does Maughan 1990 say about endurance performance?
There is a positive linear relationship between average racing speed/5km race time and VO2max
What is the Fick equation for VO2max?
VO2 = Q (a-v O2 diff)
Q = Cardiac Output a-vO2diff = Artery/Vein oxygen difference
How is Muscle VO2 measured?
- 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
What are the key limiting steps in O2 transport?
- Lungs
- Heart
- Muscles
- Mitochondria
Do lungs typically limit exercise?
Not typically. Ventilation increases more than VO2. Alveolar PO2 is maintained at maximal exercise
What has Powers et al 1989 found about the potential for the lungs to be a limiting factor for endurance performance?
- Normoxia vs Hyperoxia
- Normal group no difference in VO2max
- Highly trained group significantly higher VO2max in hyperoxia
In what two ways can a ventilation-perfusion mismatch
cause exercise induced arterial hypoxemia?
- 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
How can Pulmonary Oedema limit endurance performance?
Swelling of the interstitial fluid between capillary endothelium and alveolar epithelium increases gas diffusion distance, slowing the rate of exchange
What evidence exists to suggest that respiratory muscles limit endurance performance?
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
How is maximum inspiratory mouth pressure affected by exercise?
- 18% decrease following 20km cycling time trial (Romer et al 2002)
- 11% decrease following 6 min rowing time trial (Volianitis et al 2001)
How is the diaphragm affected by exercise?
Diaphragm fatigues during exercise above 80%VO2max, (but not voluntary hyperventilation) (Johnson et al 1996)
In summary, what is the respiratory muscle metaboreflex?
When the respiratory muscles fatigue, their blood flow needs increase, reducing the available blood flow to the legs, reducing performance
Does cardiac output limit endurance performance?
Yes. Linear relationship between cardiac output and VO2max (Liguzinski and Kozeniewski 2007)
Can muscle fuel be a limiting factor to endurance performance?
Yes. A majority of fuel at 75%+ Wmax exercise intensity is muscle glycogen. If not enough glycogenthat will reduce your performance.
Who established a positive linear relationship between Amount of Carbs in Diet, Muscle Glycogen and Time to fatigue?
Bergstrom et al 1967
