Caffeine Augments Sustained Hyperemia in Previously Exercised Leg in Male Competitive Long-Distance Runners

Blood flow in exercised skeletal muscle remains elevated postexercise, potentially playing a critical role in recovery and adaptation process. However, effective and easily implementable interventions that augment this response have yet to be identified. In this study, we investigated whether caffeine intake enhances sustained postexercise hyperemia in previously active leg in competitive long-distance runners. Ten competitive male long-distance runners participated in baseline measurements, during which cardiorespiratory responses, including leg blood flow measured by ultrasound Doppler equipment, were assessed in a supine position. Subsequently, they ingested either (a) placebo capsules or (b) capsules containing 6 mg/kg caffeine in a randomized, counterbalanced, double-blind, and crossover manner. They then completed 8-min high-intensity treadmill running at 98% of the average running speed of their estimated 10,000-m best time, followed by postexercise measurements assessing the same cardiorespiratory responses. Postexercise leg blood flow was elevated from baseline, and this response was 17% higher in caffeine relative to placebo condition (between-trial difference in average with [95% CI] = 182 [2.33, 363] ml/min, p = .048, d = 1.03). Caffeine ingestion also increased minute ventilation (2.06 [0.603, 3.53] L/min, p = .011, d = 1.17), whereas it reduced end-tidal CO2 partial pressure (-2.09 [-3.68, -0.504] mmHg, p = .015, d = 1.15) postexercise relative to placebo condition. We show that preexercise 6 mg/kg caffeine intake increases postexercise leg blood flow following high-intensity running in male competitive long-distance runners. Our results stimulate future studies to assess if caffeine-induced elevations in leg blood flow accelerates recovery and/or adaptations.