Introduction: Anthocyanin-rich blackcurrant extract altered exercise-induced metabolic responses (e.g., enhanced fat oxidation) in case studies with Caucasian non-heat acclimatized male endurance athletes. We examined 2–3 weeks before marathon competition the effects of 7-day intake of the extract (i.e., 420 mg of anthocyanins per day) during supine rest and 1 h of moderate-intensity running in an elite national level female Southeast Asian endurance athlete (age: 48 years, BMI: 19.3 kg·m−2, body fat: 21.8%, V
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: 44.4 mL·kg−1·min−1, 28 marathons since 2017) living and training outdoors in Thailand.Methods: Non-invasive beat-to-beat hemodynamic monitoring (PhysioFlow®) and breath-by-breath gas technology (Cortex Metalyzer 3B) techniques were used during supine rest and a 1-hour indoor (∼24.5 °C, relative humidity: ∼42%) treadmill run at 50%
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(7.5 km·h−1) with blood lactate (XPER L1) taken 3 min on completion. Study was single-blind and placebo-controlled with final intake of the extract 2 h before starting the treadmill run.Results: During rest, the blackcurrant extract condition was associated with higher heart rate (+6 bpm), cardiac output (+10%), carbohydrate oxidation (+31%), and respiratory exchange ratio (+0.02 units), with lower systemic vascular resistance (−18%) compared with placebo. Stroke volume, oxygen uptake, and fat oxidation values appeared similar between conditions. During the 1-h treadmill run at 50%
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, the blackcurrant extract condition was associated with higher stroke volume (+9%), cardiac output (+10%), oxygen uptake (+6%), carbohydrate oxidation (+43%), and respiratory exchange ratio (+0.03 units), with lower systemic vascular resistance (−24%) and fat oxidation (−7%) compared with placebo. Heart rate and rating of perceived exertion values appeared similar between conditions. Post-run lactate concentration was 59% lower in the blackcurrant extract condition (placebo: 1.7 ± 0.1 mMol·L−1; extract: 0.7 ± 0 mMol·L−1).Discussion: This case study provided preliminary observations that a highly endurance-trained elite National Southeast Asian female athlete responded physiologically to the intake of blackcurrant extract. Seven-day intake with 420 mg per day of blackcurrant anthocyanins was associated with alterations in cardiovascular, metabolic, and respiratory responses during rest and moderate-intensity running, including lower post-run lactate concentrations. However, the mechanisms underlying this observation remain unclear and should be interpreted cautiously given the exploratory single-participant design.