Everyone knows that caffeine can help you exercise better and longer, but most of us don’t realize that caffeine can reverse a detrimental effect that endurance exercise can have on your vision.


In a University of Waterloo study, participants experienced an almost 10 per cent reduction in their rapid eye movements after performing endurance exercise.  However, ingesting caffeine reversed the effect entirely! A group of scientists at the University of Waterloo School of Optometry and Vision Science recently explored the effects of caffeine and endurance exercise on participants’ eyesight.

To do this, they asked 11 well-trained cyclists to ride for three hours at a moderate intensity and then to take a rapid eye movement test afterwards.  Additionally, participants were given either a placebo or caffeine-infused beverage to test for moderating effects.

Cyclists given only the placebo showed an eight per cent decrease in their eye movement speed after performing the exercise session.  The decrease in eye movement is probably caused by a phenomenon known as “central fatigue,” in which the nervous system is unable to coordinate muscle movements effectively.

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However, ingesting caffeine (the equivalent of two cups of coffee) was found to counteract the effect entirely.  The members of the group that took caffeine after the workout saw their eye movements increase by nearly 11 per cent following exercise.  Although the exact mechanisms by which caffeine eliminates the effects of exercise-induced fatigue are unknown, the authors suggest that it probably affects the working of of neurotransmitters.

Most runners will agree that they feel more alert and energetic while and even after completing a run or bout of exercise.  These advantages may be especially important for early-morning runners who then drive to work or require a high degree of focus and concentration.

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