Glaister & Gissane, 2018.

doi: 10.1123/ijspp.2017-0312.

It is widely acknowledged that caffeine is the most consumed drug or psychoactive substance throughout the globe, mainly via the medium of coffee, the world’s most popular beverage, with north of a billion cups being sold daily, in saying this, in recent years the way in which caffeine is consumed has changed with the development of pre workout formulas & energy drinks. Much research has been done into the topic of just how caffeine impacts sports performance, and what we know for sure is that it has a net positive impact, exactly how this is achieved is still debated.

This blog is mainly going to focus on the paper published in the journal of human kinetics in 2018 which looked at the effects of caffeine on physical parameters of sports performance, with one or two other factoids making an appearance along the way. Before we get into the nitty gritty I just want to point out some general things in relation to the usage of caffeine as an ergogenic aid (a substance that enhances sports performance). It is accepted that typical doses of caffeine to see a benefit in any sport, whether it be long steady state, field sports or repeat sprint efforts, is accepted as 3-6mg/kg, to put this into context, an 80kg man would have to consume the equivalent of a triple espresso to have any tangible benefit on his sporting performance (that’s a lot of coffee), caffeine takes about 45mins to peak in your blood stream if consumed as a drink like coffee, and as little as 15mins if consumed as caffeine gum or powder, which tend to be dosed in around 150-200mg per serving.

Consuming in excess of 500mg daily can lead to negative health consequences (this is about 6 coffees) whereas getting above 600mg daily may trigger a positive doping test. The sweet spot from a health perspective is not necessarily noted for caffeine itself, but for coffee, it is 3 a day for maximal protection against all cause mortality, liver fat buildup and dementia. Back to the task at hand.

You have likely done the maths in your head already and figured out how much caffeine you might need, and when you should be taking it, if you are satisfied and are not interested in the science, go forth and caffeinated yourself. If you are a habitual coffee drinker, and are wondering (as I am always asked this) if that will make caffeine supplementation less effective for you, the answer is no, caffeine supplementation at higher doses equally effects those who do and do not consume caffeine, with no difference in terms of enhancement of performance between those who drink the equivalent of one weak cup and those who drink 2-3 stronger cups daily. Now really, back to the research paper.

This study was a meta analysis, basically this means it pooled together a bunch of studies on the topic of caffeine supplementation, amalgamates all of the results to make broader conclusions, in most cases this is seen as the highest form of evidence, though it is not always ideal for nutrition based studies. 26 double blinded studies were included, with the most common dosage being 5-6mg/kg, which is the first caveat, as this is an uncommonly high ingestion rate, and for many it’s unrealistic from a tolerance point of view (and safety depending on weight), with the most common ingestion time being 60mins pre workout. The majority of the studies were done in cyclists and runners, with the exercise intensity ranging from 60-85% VO2max, or steady state aerobic range.

The findings of the study were as follows:

  1. No difference in effect between males & females
  2. Prior habitual caffeine consumption appeared not to be an issue in it’s effect
  3. Caffeine versus placebo saw significant increases in minute ventilation, blood glucose levels & blood lactate levels
  4. Caffeine versus placebo saw significantly lower ratings on the perceived effort scale
  5. There were no differences in heart rates or fat oxidation rates

The interesting thing that this study posits is that the subjects using caffeine were breathing heavier and at a higher rate per minute (minute ventilation) but were perceiving the exercise to be lower in it’s effort to complete it. There are still some unknowns about the mechanisms by which caffeine exerts it’s effect, what is thought to be a possibility is that adenosine (which is displaced by caffeine as it binds to adenosine receptors instead) can disrupt glucose clearance and glycolysis levels, having a clear impact on blood glucose levels. With blood glucose levels rising this would posit a logical basis to point to the cause of the increased lactate levels in the blood.

The final piece of the puzzle is that caffeine changes how sensitive chemoreceptors are to CO2 buildup in the bloodstream, prompting a higher minute ventilation rate versus placebo to lower this (you do not want high levels of CO2 in your blood), possibly accounting for the mismatch between minute ventilation rate, fat oxidation and blood glucose levels. This data is mechanistic in nature and has a number of hypothetical elements yet to be fully elucidated in the research.

Just for reference, a bottle of coke is about 40mg of caffeine, a cup tea is about 40-60mg, an espresso shot is about 80mg, a double is 160mg & an aeropress can be anywhere from 140-200mg depending on brew time and amount of grind used. Lighter roast coffees tend to give off high caffeine contents.

Brass tax – caffeine works, we just don’t completely know how yet.

Enjoy your cuppa.