Week 10 - Caffeine

Question 1

Where is caffeine metabolised?

Answer 1

in the liver
1,3,7 trimethylxanthine

Question 2

Common sources of caffeine.

Answer 2

Coffee
Green teas
Chocolate
Caffeine drinks (red bull)
Sports drinks
Gels
Gum
Capsules

There is a variation in caffeine content, especially with coffee/tea.

Question 3

What was the previous limit of caffeine proposed by WADA? Why was this removed from WADA list in 2004?

Answer 3

12ug/mL
Due to individualized metabolism rate of caffeine

Question 4

When does peak blood caffeine concentrations typically occur? However, when are benefits experienced?

Answer 4

60mins after ingestion in a dose-dependent way.
Benefits occur soon after intake before reaching peak blood concentration.

Question 5

What are the effects of caffeine?

Answer 5

• Improved vigilance and alertness
• Reduced perception of effort
• Reduced fatigue and perception of pain
  = Improved performance

Question 6

Outline the 3 proposed mechanisms of how caffeine works.

Answer 6

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.

Question 7

Explain the “Muscle ion effect” mechanism of caffeine action.

Answer 7

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.

Question 8

When does caffeine seem to increase the release of intramuscular calcium ions which are responsible for muscle contraction?

Answer 8

with very high doses of caffeine

Question 9

Explain the “Metabolic effect” mechanism of caffeine action.

Answer 9

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

Question 10

What is the limitation of both the metabolic and muscle ion mechanisms of caffeine action?

Answer 10

they both require high doses

Question 11

Explain the MOST important “Central effect” mechanism of caffeine action?

Answer 11

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.

Question 12

What are the effects of caffeine consumption with carbohydrates?

Answer 12

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.

Question 13

What is an advantage of using caffeinated gum?

Answer 13

most of the caffeine bypasses the gut which increased absorption and decrease GI distress.

Question 14

What is the optimal dose of caffeine for enhancing athletic performance?

Answer 14

1.5 to 3mg/kg body mass

Larger amounts do not seem to provide an extra benefit and may increase side effects.

Question 15

When is it recommended to consume caffeine?

Answer 15

• 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)

Question 16

Are the actions of caffeine influenced by the level of habitual caffeine consumption? But?

Answer 16

No - caffeine habitual consumption does not affect ergogenic effects, only when high doses are consumed (6mg/kg BM). When lower doses (3mg/kg) are consumed this is not the case.

Question 17

What can caffeine be co-ingested with to benefit performance (ergogenic effect)?

Answer 17

carbohydrates (co-ingestion is ergogenic) can lead to reduced TT time (mins)
e.g. Coke contains caffeine and 11% CHO.

Question 18

What does ingesting caffeine in drinks contribute to?

Answer 18

Hydration

Question 19

When should you consider the use of caffeine?

Answer 19

 Endurance sports (> 60 min)
 Brief sustained high-intensity
sports (1-60 min)
 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

Question 20

Why is caffeine recommendation dependent on genetics?

Answer 20

• Caffeine metabolization speed differs.
• Nervous system excitability differs.

Question 21

What is a potential risk of caffeine ingestion?

Answer 21

Sleep: It can affect sleep onset and quality which can interfere with the athlete’s recovery between training sessions, or during multi-day competitions.

Hydration: small to moderate doses of caffeine have minimal effects on urine losses or overall hydration. Additionally, caffeine-containing drinks (tea, coffee, coke) contribute to fluid intake.

Question 22

What is the half-life of caffeine?

Answer 22

5 hours - the amount of time it takes for a quantity of caffeine to be reduced to half the original amount in the body.

Question 23

At moderate and high doses of caffeine (>6-9mg/kg), what side effects can occur?

Answer 23

• Anxiety
• Jitters
• Insomnia
• Inability to focus
• GI unrest
• Irritability

There is a dependency to caffeine - anxiety and sleep disorders, withdrawal effects can occur.

Question 24

What is a safe dose of caffeine to ingest?

Answer 24

400mg/day from all sources and 200mg at any one time

Question 25

Children (<18yrs) are suggested to limit caffeine intake to …

Answer 25

<2.5mg/kg/day