Author(s): NISHIKAWA, M., NISHIYASU, T., SHIBASAKI, M., FUJII, N., Institution: UNIVERSITY OF TSUKUBA, Country: JAPAN, Abstract-ID: 949

INTRODUCTION:
Caffeine, which can modulate physiological and perceptual responses and improve exercise performance, is widely used in intermittent high-intensity sport. In applied settings such as team sports and tournament play, athletes often perform multiple high-intensity bouts separated by prolonged recovery, creating uncertainty regarding optimal caffeine supplementation strategies. It remains unclear whether a single pre-exercise caffeine dose maintains ergogenic and physiological effects when high-intensity exercise is repeatedly performed. Clarifying this would provide valuable insights into strategies to maximise caffeine's ergogenic effects. This study examined whether a single dose of caffeine (6 mg/kg) sustains repeated-sprint cycling performance up to 3 h post-ingestion and assessed the associated plasma noradrenaline, ventilatory, cardiovascular, and cerebral haemodynamic responses.
METHODS:
Twelve healthy adults (4 females) completed randomised, double-blind, placebo-controlled, crossover trials following caffeine (6 mg/kg) or placebo ingestion. At 60, 120, and 180 min post-ingestion, participants performed 5 min moderate-intensity cycling (50% heart rate reserve) followed by repeated sprinting (6 x 5 s). Plasma samples were collected repeatedly for caffeine and noradrenaline analysis. Middle cerebral artery mean blood velocity (MCAVmean) was measured via transcranial Doppler, and common and internal carotid artery blood flow were assessed at rest using ultrasound. Respiratory and cardiovascular variables, ratings of perceived exertion (RPE), and leg muscle pain were recorded.
RESULTS:
Plasma caffeine concentrations increased by 30 min post-ingestion and remained elevated throughout the protocol. Caffeine increased peak and mean sprint power output compared with placebo across all sprint sets performed at 1, 2, and 3 h post-ingestion, with peak power enhanced by up to 3.8%. These performance benefits were accompanied by attenuated perceptual strain, including lower RPE and reduced leg muscle pain. During sprint exercise, plasma noradrenaline concentrations were higher with caffeine from the first to the final sprint set. MCAVmean was lower with caffeine throughout the protocol, coinciding with reductions in end-tidal partial pressure of CO2 and resting common and internal carotid artery blood flow.
CONCLUSION:
A single pre-exercise ingestion of 6 mg/kg caffeine enhances repeated-sprint ability for at least 3 h post-ingestion. These findings suggest a single dose provides sustained ergogenic effects for repeated sprinting without additional caffeine. Prolonged effects on plasma noradrenaline, cerebral blood flow, and perceptual responses were also observed, and these effects may contribute to the aforementioned enhanced performance, although direct investigation is warranted. We show that a pre-exercise intake of 6 mg/kg caffeine improves sprint performance and modulates sympathetic cardiorespiratory and perceptual responses during prolonged intermittent exercise over 3 h.