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Charlotte Connell, Benjamin Thompson, Shelley Duncan, Michael Claffey, Gustav Kuhn, Nicholas Gant; Fatigue-induced impairments in saccade velocity are reversed by caffeine. Invest. Ophthalmol. Vis. Sci. 2013;54(15):184.
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We have recently shown that prolonged strenuous exercise can decrease the velocity of saccades. This kinematic impairment of eye movements suggests that ocular motor control may be susceptible to central fatigue. Here we repeat the exercise protocol and administer caffeine, a CNS stimulant with fatigue-reversing properties, to assess the extent to which the neural control of eye movement is modified by central fatigue.
Within a double-blind, randomized, cross-over design, 10 cyclists (mean age 23 years) consumed either a placebo or caffeine solution during a 180 min cycling exercise protocol. The exercise workload was calibrated equivalent to 60% of each participant’s maximum aerobic capacity. Saccadic eye movements and global motion perception, assessed within the context of an established social attention paradigm, were measured before and after the exercise protocol. Eye movements were recorded using an infra-red eye-tracker. Heart rate and perceived exertion were recorded throughout the duration of the protocol. Hydration status, handgrip and leg strength were also assessed.
Exercise-induced fatigue decreased saccade velocity by 5% (placebo trial), whilst velocity increased by 10% during the caffeine trial (F1, 10=7.594, P<0.05). Mean saccade velocity was enhanced above baseline levels with caffeine for both congruent and incongruent saccades. Neither fatigue nor caffeine influenced saccade accuracy, global motion perception or the effects of social attention on the latency of eye movements. Caffeine lowered perceived exertion (F 10, 100 = 6.915, P<0.05) and increased felt arousal (F10, 100 = 6.855, P<0.05). Fatigue reduced leg strength for both treatments (F1, 9 = 12.680, P<0.006).
The human visual system appears to be susceptible to exercise-induced central fatigue. A moderate dose of caffeine improves saccadic eye movement velocity in the presence of fatigue. This is likely related to the ability of caffeine to alter central neurotransmission and ameliorate 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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