It's not only the legs that feel the effects of cycling; a new study suggests it can put a strain on the eyes, too. But don't get off your bike just yet. The study also found that drinking coffee might prevent such an effect.
Study leader Dr. Nicholas Gant, of the University of Auckland in New Zealand, and colleagues recently published their findings in the journal Scientific Reports.
Prolonged cycling, for example, can trigger central fatigue, which normally presents through tiring of the legs.
But while it is well known that central fatigue affects limb movement, Dr. Gant and colleagues note that it is unclear whether it impacts other motor systems, such as those involved in eye movement.
To find out, the team enrolled 11 well-trained cyclists, who cycled using exercise bikes for 3 hours.
The researchers explain that caffeine can indirectly boost the activity of certain neurotransmitters - chemicals that relay signals between brains cells - and note that previous studies have suggested that impairments in neurotransmitter activity might be responsible for central fatigue.
Once participants had finished cycling, the researchers tested their eye movement using a head-fixed eye-tracking system.
Impaired eye movement was restored with caffeine
The team found that the strenuous exercise the participants engaged in caused a neurotransmitter imbalance, which slowed down the subjects' rapid eye movements.
"Interestingly, the areas of the brain that process visual information are robust to fatigue. It's the pathways that control eye movements that seem to be our weakest link," says Dr. Gant.
"These results are important because our eyes must move quickly to capture new information," he adds. "But there's hope for coffee drinkers because this visual impairment can be prevented by consuming caffeine."
The researchers found that participants who consumed the caffeinated beverages saw their neurotransmitter balance restored, which improved their rapid eye movements. No such effect was found among subjects who drank the decaffeinated solution.
Commenting on their findings, the authors say:
"This is the first study to show impaired control of eye movements following fatiguing exercise. Prolonged use of the skeletal motor system influences the function of the oculomotor system, implicating a possible role of central fatigue.
Caffeine is capable of countering this effect, suggesting that central fatigue may be related to a disruption in the balance of one or more excitatory and inhibitory neurotransmitters."
The researchers are now in the process of investigating whether psychiatric drugs - which work by restoring neurotransmitter levels - might be effective for treating fatigue caused by strenuous exercise.