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Abstract

Caffeine is commonly used among athletes for its performance-enhancing effects. However, its impact on fat oxidation in overweight/obese individuals during exercise at maximal fat oxidation intensity (FATmax) is not well understood. PURPOSE: To examine the effects of different doses of acute caffeine ingestion on fat oxidation and cardiovascular response in overweight/obese female college students during exercise at FATmax. METHODS: Eleven overweight/obese female college students participated in four trials after ingesting caffeine (3 mg/kg, 5 mg/kg, 9 mg/kg) or a placebo (cellulose). Each trial included 1 hour of rest and 40 minutes of continuous running at FATmax. Fat and carbohydrate oxidation were measured using indirect calorimetry, while blood pressure and fingertip perfusion index (PI) were assessed at rest (0, 30 and 60 minutes) and 40 minutes post-exercise. RESULTS: Caffeine had no effect on heart rate and fat/carbohydrate oxidation at rest. During exercise, both medium (5 mg/kg) and high-dose (9 mg/kg) caffeine significantly increased heart rate and blood pressure (p < 0.05), while the low-dose (3 mg/kg) group had no effect. PI decreased in all caffeine groups (p < 0.05). Low and medium doses increased fat oxidation compared to placebo and high-dose groups (p < 0.05). Carbohydrate oxidation was reduced in the medium-dose group compared to placebo (p < 0.05) and was lower in both low and medium-dose groups than in the high-dose group (p < 0.05). CONLUSION: Caffeine’s effects on fat oxidation and cardiovascular responses vary with dosage. Low-dose caffeine (3 mg/kg) is recommended during exercise at FATmax for optimal fat reduction and minimal cardiovascular side effects in overweight/obese female college students.

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