W7 - Stimulant Supplements incl. Caffeine (NEW) Flashcards
Stimulants stimulate the CNS with a marked effect on what?
Mental function + behaviour
Produces excitement + euphoria
⬇️ sensation of fatigue
⬆️ motor activity
Roughly how long does it take for caffeine to reach peak plasma concentration after consumption?
What does this mean?
~1hr
Means people tend to take caffeine an hour prior to our req to get ergogenic effects.
What is caffeines half life
~5hrs
What is the half life of caffeine informed by to some extent?
Liver function
What happens in regards to caffeine half life with someone who has hepatic dysfunction?
Tend to have a longer half life due to 1 of livers key roles being to detoxify substances like caffeine.
As well as liver function, what else has a role in influencing the metabolism of caffeine?
Habituation
- Those who are caffeine naive will respond differently.
What % of athletes have been reported to consuming caffeine before or during competitive events?
75-90%
What is the habitual consumption of caffeine among athletes?
~300mg/day from just normal dietary sources.
What are the 3 mechanisms by which caffeine operates?
⬆️ central drive from brain to muscle
⬆️ FA levels in blood
Influencing kinetics of Ca2+ in muscle
MECHANISMS BY WHICH CAFFEINE OPERATES
Central effects (⬆️ central drive from brain to muscle)
What is meant by this?
Adenosine has a calming effect.
Caffeine is suggested to bind to adenosine receptors in the brain.
This displaces adenosine from the receptors to give a stimulant effect.
MECHANISMS BY WHICH CAFFEINE OPERATES
⬆️ FA levels in blood
How?
Due to activating the sympathetic NS to ⬆️ rate of lipolysis.
⬆️ release of noradrenaline through activation of sympathetic NS.
⬆️ noradrenaline activates LPL enzymes responsible for lipolysis.
⬆️ Lipolysis = ⬆️ glycerol + FA into blood.
MECHANISMS BY WHICH CAFFEINE OPERATES
Influence of Ca2+ kinetics in muscle
Explain
Could be promoting the reuptake of Ca2+ into the sarcoplasmic reticulum.
= Might ⬆️ contractility of muscles = more powerful contraction.
Some evidence to suggest that caffeine might result in lower extracellular K+
Why is this beneficial?
High intensity exercise ⬆️ extracellular K+ (which actually contributes to the development of fatigue).
So… caffeine can help preserve the excitability of the muscle = improve perf.
Overall effects of caffeine
⬆️ max + submax perf
Delays fatigue
May ⬆️ contractility
⬆️ voluntary activation
== Particularly helpful where central fatigue is a key cause of poor performance?
What impact does caffeine have on lipolysis?
Stimulates it at REST
Does caffeine have any metabolic effects?
No
What impact does caffeine have in plasma K+?
Lowers it
According to Shen et al, 2019, what effect does caffeine have on TT performance?
Enhances it by ~3% compared to placebo.
Are the magnitude of the effects of caffeine influenced by the characteristics of the participants?
no
What is caffeine supplementation not effective for?
800m perf
Effect of caffeine on team sports perf
Improves it
Performance effects summary of caffeine supplementation
Improved endurance perf.
Improved team sport performance
Improvement in movement velocity + resistance exercise performance.
What is the effective dose of caffeine?
3-6 mg per kg of body weight
What does the exact dose of caffeine supplementation depend on?
Sex, mode, timing + habituation
What are the modes for caffeine supplementation
Ingestion (pill or drink)
Chewing gum
Patch
Diuretic effects from caffeine supplementation
Moderate diuretic effects at rest but NOT in exercise trials.
Females are more susceptible
Alternative stimulants to caffeine
Guarana
Yerba Mate
Ginseng
