One of key mechanisms behind caffeine's effectiveness is the blocking of adenosine binding to adenosine receptors. To combat habitual use of this the body will up-regulate (produce more) receptors potentially blunting effects. Combined with this the body is also capable of increasing the induction speed of a key enzyme in the metabolism of caffeine in the liver. Combined, it is possible that these mechanisms could blunt the effects of caffeine and also remove it from your system faster. Nightmare.
So, is the above actually harming the performance improving effects? Well, research has been pretty limited in this area and actually fairly undecided. An early study in 1991 (Tulley, R et al, 1991) compared non habitual users (<25mg/day) against habitual users (>300mg/day). All participants completed a time to exhaustion test under 3 conditions (placebo, 3mg/kg & 5mg/kg). What this showed was that there was no difference in time to exhaustion between the caffeine protocols indicating that there was no blunting effect.
However a more recent study (Watson, P. et al., 2017) controlled for more variables by administering a pre-testing caffeine loading period or placebo for 28 days. After this period all participants ingested 3mg/kg and completed a 60 min cycle at 60% of VO2peak followed by a 30 minute maximum cycle. When compared there was actually a 7.3% reduction in total work produced by habitual caffeine users compared to non- regular users. However, there still exhibited a positive effect when compared against the placebo group.
Overall it is important to note that research in this area is pretty grey and there are really only a smattering of studies with very different study designs test groups. Many of the habitual caffeine consumers were consuming between 4 & 4.5mg/kg daily. If you look back at our earlier posts then you will hopefully be aware that this kind of dose is not needed to induce performance improvements and that 3mg/kg is more than enough in many cases.
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So what should athletes do from here on in? Well, the common misconception is that you should withdraw from regular consumption in the lead up to a competition so that you can re-sensitise yourself. If you look at the table below you will see that a number of studies have looked at this question but there were no significant findings after various 'washout' and pre-trial doses. Considering that for many withdrawal may results in negative outcomes we do not recommend that you partake in a pre competition washout period.
If you have read our last log detailing how to personalise your caffeine approach then your intake should fluctuate between training days anyway depending on the training modality. I.e. Endurance day = 3m/kg compared to a strength day which could be closer to 6mg/kg. If you are a habitual user then rather than weaning yourself off prior to competition we recommend you prepare to increase your regular by 50%+. This was cautiously echoed by caffeine researchers Craig Pickering & John Kiely (2018), although they recommended doubling your regular dose, which seems excessive.