"What's interesting," Motl said, "is that when we found that caffeine tolerance doesn't matter, we were perplexed at first. Then we looked at reviews of the literature relative to caffeine and tolerance effects across a variety of other stimuli. Sometimes you see them, sometimes you don't. That is, sometimes regular caffeine use is associated with a smaller response, whereas, other times, it's not."
No one's been able to figure out the reason for the inconsistency, Motl said.
"Clearly, if you regularly consume caffeine, you have to have more to have that bigger, mental-energy effect. But the tolerance effect is not ubiquitous across all stimuli. Even brain metabolism doesn't show this tolerance-type effect. That is, with individuals who are habitual users versus non-habitual users, if you give them caffeine and do brain imaging, the activation is identical. It's really interesting why some processes show tolerance and others don't."
Regarding the outcome of the current research, he said, "it may just be that pain during exercise doesn't show tolerance effects to caffeine."
Motl said one of the next logical steps for his research team would be to conduct studies with rodents in order to better understand the biological mechanism for caffeine in reducing pain.
"If we can get at the biological mechanism, we can begin to understand why there may or may not be this kind of tolerance."
Motl said another research direction might be to determine caffeine's effect on sport performance.
"We've shown that caffeine reduces pain reliably, consistently during cycling, across different intensities, across different people, different characteristics. But does that reduction in pain translate into an improvement in sport performance?"
Meanwhile, the current research could prove encouraging for a range of people, i
|Contact: Melissa Mitchell|
University of Illinois at Urbana-Champaign