Connell, C. J., Thompson, B., Duncan, S., Claffey, M. P., Khun G., & Gant, N. (2014). Fatigue-induced impairments in eye-movement velocity are reversed by caffeine. Medicine & Science in Sports & Exercise, 46(5), Supplement abstract number 2754.

"Three hours of prolonged cycling exercise can decrease the velocity of voluntary saccades (rapid eye movements that direct the fovea towards an object of interest). This impairment of an exercise-independent motor system demonstrates that fatigue is ubiquitous within the brain. In this study we repeat the experimental protocol and administer caffeine, a CNS stimulant with fatigue-reversing properties, to assess the extent to which the neural control of eye movements are influenced by alterations in central neurotransmission."

Ten cyclists participated in a double-blind, randomized, cross-over design. Ss consumed solutions delivering 7 g/kg/h carbohydrate (placebo condition) or isoenergetic taste-matched caffeine-carbohydrate solutions (5 mg/kg-1caffeine) during a 180-minute cycling exercise protocol. The exercise workload was equivalent to 60% of each S’s maximum aerobic capacity. Saccadic eye movements were assessed within the context of an established social attention paradigm, with measurements collected before and after the exercise protocol. Eye movements were recorded using an infra-red eye-tracker. Global motion perception was measured using a random dot kinematogram. Physiological and perceptual measures were collected at routine intervals throughout the protocol.

Exercise-induced fatigue decreased saccade velocity by 7.9% in the placebo trial, whilst velocity increased by 10.9% during the caffeine trial. Caffeine lowered perceived exertion and increased arousal. There were no differences between trials in global motion perception.

Implication. "The human visual system is susceptible to exercise-induced central fatigue. A moderate dose of caffeine improves saccadic eye movement velocity in the presence of exercise-induced fatigue. That is likely related to caffeine’s ability to alter central neurotransmission, thus ameliorating the effects of central fatigue on ocular-motor control. Neural processing of visual information is robust to both exercise-induced fatigue and caffeine supplementation."

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