Week 10 - Caffeine Flashcards
Where is caffeine metabolised?
in the liver
1,3,7 trimethylxanthine
Common sources of caffeine.
Coffee
Green teas
Chocolate
Caffeine drinks (red bull)
Sports drinks
Gels
Gum
Capsules
There is a variation in caffeine content, especially with coffee/tea.
What was the previous limit of caffeine proposed by WADA? Why was this removed from WADA list in 2004?
12ug/mL
Due to individualized metabolism rate of caffeine
When does peak blood caffeine concentrations typically occur? However, when are benefits experienced?
60mins after ingestion in a dose-dependent way.
Benefits occur soon after intake before reaching peak blood concentration.
What are the effects of caffeine?
- Improved vigilance and alertness
- Reduced perception of effort
- Reduced fatigue and perception of pain
= Improved performance
Outline the 3 proposed mechanisms of how caffeine works.
1) Central effect: Caffeine prevents adenosine binding to its receptors in the CNS, reducing sensations of tiredness/fatigue.
2) Metabolic effect: Caffeine stimulates lipolysis directly and indirectly, with possible carbohydrate sparing.
3) Caffeine stimulates calcium release.
Explain the “Muscle ion effect” mechanism of caffeine action.
Caffeine increases the release of intramuscular calcium ions which are responsible for muscle contractions. However, this seems to happen with very high doses of caffeine.
When does caffeine seem to increase the release of intramuscular calcium ions which are responsible for muscle contraction?
with very high doses of caffeine
Explain the “Metabolic effect” mechanism of caffeine action.
Caffeine stimulates lipolysis (breakdown of triglycerides) directly and via an increase in adrenaline. This may spare muscle glycogen but only in certain conditions:
- 9mg/kg
- High W
- Early in exercise
What is the limitation of both the metabolic and muscle ion mechanisms of caffeine action?
they both require high doses
Explain the MOST important “Central effect” mechanism of caffeine action?
When adenosine binds to its receptors, this causes feelings of tiredness, fatigue and even pain sensation.
Caffeine has a similar chemical structure to adenosine therefore it stops adenosine binding to the receptors in the brain, reducing the sensations of tiredness and pain thereby delaying fatigue.
Through this mechanism, caffeine can improve performance in a wide variety of sports (endurance, power, high-intensity) without the need of high doses.
What are the effects of caffeine consumption with carbohydrates?
No effect on substrate metabolism but it has performance benefits such as increase power and a reduced TT time on a cycling task - these benefits are NOT due to metabolic actions of caffeine.
What is an advantage of using caffeinated gum?
most of the caffeine bypasses the gut which increased absorption and decrease GI distress.
What is the optimal dose of caffeine for enhancing athletic performance?
1.5 to 3mg/kg body mass
Larger amounts do not seem to provide an extra benefit and may increase side effects.
When is it recommended to consume caffeine?
- 40-60mins before the event or exercise
- Throughout event at lower doses (1.5mg/kg)
- Late during the event, or before an important stage of the event (100-200mg) (moderate dose of 2.9mg/kg was more effective late in exercise compared to low dose of 1/5mg/kg)
