Caffeine Flashcards
1
Q
what is caffeine
A
- 1, 3, 7-trimethylaxanthine -> metabolised in the liver
- commonly consumed drug
- removed from WADA list in 2004 (previously 12 ug/mL limit)
- sources: coffee, green tea, chocolate, sugary/energy drinks
2
Q
bio-availability
A
- peak blood caffeine concentrations typically occur ~60 min after ingestion in a dose-dependent way
- however, benefits from caffeine can occur soon after intake (before reaching peak blood concentrations)
3
Q
what are the effects
A
- improved vigilance and alertness
- reduced perception of effort
- reduced fatigue and pain
= improved performance (high individual variability)
4
Q
proposed mechanisms
A
- when adenosine binds to its receptor, this causes fatigue. caffeine prevents adenosine binding and thereby delays fatigue
- caffeine stimulates lipolysis (breakdown of triglycerides), directly and via an increase in adrenaline. this may spare muscle glycogen
- caffeine stimulates calcium release which is important for muscle contraction
5
Q
muscle ion effect: increase in calcium release in muscle
A
- caffeine increases the release of intramuscular calcium ions (Ca2+) responsible for muscle contractions, although this seems to happen with very high doses of caffeine
- it was thought that caffeine supplementation might be able to increase muscle force generation, but this outcome is not consistent acrpss studies
6
Q
metabolic effect: increase in fat mobilisation and oxidation
A
caffeine can directly (increased triglycerides breakdown) or indirectly (increased epinephrine) stimulate fat metabolism
7
Q
central effect: blocking adenosine
A
- caffeine has similar chemical structure to a molecule called adenosine (responsible for feelings or tiredness, fatigue and even pain sensation)
- therefore, caffeine can stop adenosine from binding to its receptors in the brain, reducing the sensations of both tiredness and pain
8
Q
caffeine content
A
- the content of caffeine varies across different sources, and it can vary within the same source
- tea and coffee are good sources of caffeine, but actual caffeine content can vary markedly depending on the preparation mode
- for exact caffeine content, supplements (batch tested) are recommended
9
Q
caffeine sources
A
caffeine, delivered in any form, can improve various aspects of performance. an advantage of using caffeinated gum is that most of the caffein bypasses the gut (increased absorption, decreased GI distress)
10
Q
amount
A
- the optimal dose for enhancing athletic performance appears to be ~3mg/kg BM
- (same as the optimal dose for enhancing cognitive function)
- larger amounts do not seem to provide an extra benefit and may increase side effects
11
Q
timing
A
- usually ~40-60 min 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)
12
Q
when to consider its use
A
- endurance sports (>60mins)
- brief sustained high-intensity sports (1-60min)
- team and intermittent sports - work rates, skills and concentration
- single efforts involving strength or power
- pre-training energy boost if carrying fatigue into a session
13
Q
risks
A
- sleep
- caffeine can affect sleep onset and quality (even at low levels of intake), which may interfere with the athletes recovery between training sessions, or during multi-day competitions. the timing of caffeine intake relative to the need for sleep should be considered
- hydration
- small to moderate doses of caffeine have minimal effects on urine losses or overall hydration in habitual caffeine users. in addition, caffeine-containing drinks such as tea, coffee and cola drinks contribute to fluid intake
- at moderate and high doses of caffeine (>6-9mg/kg) other side affects can occur: anxiety, jitters, insomnia, inability to focus, GI unrest, irritability
- there is a dependency to caffeine - anxiety and sleep disorders, withdrawal effects can occur
