Central fatigue was observed to reduce the velocity of saccadic eye movements by 8%, an effect which was reversed by a moderate dose of caffeine.
Strenuous or prolonged exercise can temporarily trigger a type of tiredness called central fatigue, a state which is characterized by weakened skeletal muscles and reduced exercise performance. While the molecular mechanisms behind this phenomenon are not well understood, it is believed that it is associated with alterations in the levels of serotonin, dopamine, and noradrenaline neurotransmitters of the central nervous system. The impact of central fatigue on the oculomotor system after exercise is unknown, but has been linked to a reduction in the velocity of saccadic eye movements, which are quick, jerky eye movements that are used to explore the salient features of a visual target.
The impact of central fatigue on the oculomotor system after prolonged exercise was examined in a recent article in Scientific Reports. Twelve trained cyclists participated in an experimental trial involving 3 hours of continuous stationary cycling at a rate of 60% of their maximal aerobic capacity to provide a physical challenge capable of inducing central fatigue. Baseline measures for muscle force and saccades were obtained prior to and immediately following exercise. Following a double-blind protocol, participants drank a carbohydrate solution every 15 minutes (placebo condition) or the same solution with a moderate dose of caffeine added 90 minutes after the cycling had started to explore the involvement of central neurotransmitters (caffeine condition). Post-exercise, participants completed oculomotor and non-oculomotor tasks, including a saccade visual task which was measured using infra-red technology.
Saccade velocity in the placebo condition significantly slowed by 8% after prolonged exercise compared to baseline measures. With the administration of caffeine, it was discovered that saccade velocity remained either equivalent to baseline levels, or in some cases, increased moderately. There were no changes observed in saccade latency, accuracy, or error pre- to post-exercise or between interventions, and non-oculomotor visual tasks were not affected by central fatigue.
This study is significant because it is the first to demonstrate that eye movements are impaired following fatiguing exercise, and indicates that skeletal system fatigue also impacts oculomotor system control. Caffeine is a central nervous system stimulant which affects the rate of noradrenaline synthesis and enhances of dopamine release, and in this study, was able to offset the effects of central fatigue on eye movements. These results support the hypothesis that central fatigue is related to the disruption of these neurotransmitters, and can in turn affect oculomotor regions and processes involved in saccadic control.
Written By: Fiona Wong, PhD