New research from the University of Waterloo's School of Optometry has found that intense exercise that leaves you feeling exhausted can affect your vision.

Dr. Ben Thompson, a professor in the school of optometry and vision science who conducted the study, told The Morning Edition's host Craig Norris that the study showed that fatigue can strike in unexpected ways - and that there may be a solution.

Participants in the study were asked to cycle for three hours using 60 per cent of their maximum ability. Afterwards, the study measured their ability to move their eyes, particularly the speed their eyes moved.

"We found a 10 per cent reduction in the speed of their eye movements," said Thompson. "We measured a half an hour after the exercise and the impairment was still there. It's possible that it could last for an extended period of time."

Exercise fatigue

After exercising a certain part of the body, over time a person will notice they are less able to move it. This has partly to do with the muscles in the body but, Thompson says, "the brain gradually turns down the volume of the signals that it sends to that part of the body." Meaning, the fatigue a person feels is has to do with the changes in their brain and not their body.

Thompson applied this concept to see if it was the same for other moving parts of the body, particularly in a person's vision. Exercise changes the chemicals that help the brain parts communicate with each other.

"It seems this mechanism we're studying is where the brain turns down the signals in general," he said. "That was the question we wanted to ask with this study. Is it just affecting the part of the body that's moving? Or does it affect the brain as a whole? That's why we traced the eyes."

Keeping the brain alert

The study found that when participants consumed caffeine half way through the exercise, it not only surpassed the exercise effect, it ended up increasing their eye movement.

"It seems to reset the changes in the brain that occur with exercise and our movement," Thompson said.

He adds that the next step of the study will include figuring out the real world implications while trying to understand what caffeine does to the brain, by looking at drugs that have a more targeted effect.

Hear more about this story on Quirks and Quarks at noon ET on CBC Radio One. Click here to listen online.