From Ergo Log
No matter how physically fit and well rested you are, if you are mentally tired you’ll perform less well. Sports scientists from the British Bangor University reach this conclusion in an article published in the Journal of Applied Physiology. So before you start training you should make sure you give your brain a rest.
Although it would seem logical that mental fatigue leads to worse physical performance, hardly any research has ever been done on the relationship between mental fatigue and sport. The most recent reference that the British researchers could find in the literature dates back to 1891, when the Italian physiologist Angelo Mosso published his standard work La Fatica, in which he describes how researchers performed less well after they had spent the whole day supervising oral exams.
The British researchers did an experiment with sixteen reasonably fit amateur athletes. One lot watched documentaries for an hour and a half on the history of Ferraris and the Orient Express train. The other group had to do a challenging mental agility test for an hour and a half. After each session the test subjects had to cycle at 80 percent of their VO2max.
The athletes that had watched documentaries managed to cycle for 12 minutes and 34 seconds. The athletes that had tired themselves out mentally only lasted for 10 minutes and 40 seconds.
The researchers found no physiological differences between the athletes: heart rate, blood pressure and volume of blood pumped by the heart were all near enough the same. The only parameters for which the researchers did find differences – like the amount of lactic acid in the blood – only became visible towards the end of the trial, and were caused by the fact that the documentary group cycled for longer than the mentally tired group.
What the researchers did notice was that the mentally rested group did not become more tired, whereas the mentally tired group became more fatigued as a result of the physical exertion. The figure below shows how tired the test subjects felt.
The researchers suspect that mental fatigue changes something in the way the brain registers signals of physical exhaustion. If you are mentally tired, your brain interprets signals of physical exhaustion as being more serious than they actually are. “Brain function can limit short-term endurance performance in thermoneutral conditions”, the Brits conclude.
J Appl Physiol. 2009 Mar;106(3):857-64.