The study examined caffeine (5 mg/kg body weight) vs. placebo during anaerobic exercise. Eighteen male athletes (24.1 ± 5.8 yr; BMI 26.4 ± 2.2 kg/m2) completed a leg press, chest press, and Wingate test. During the caffeine trial, more total weight was lifted with the chest press, and a greater peak power was obtained during the Wingate test. No differences were observed between treatments for the leg press and average power, minimum power, and power drop (Wingate test). There was a significant treatment main effect found for postexercise glucose and insulin concentrations; higher concentrations were found in the caffeine trial. A significant interaction effect (treatment and time) was found for cortisol and glucose concentrations; both increased with caffeine and decreased with placebo. Postexercise systolic blood pressure was significantly higher during the caffeine trial. No differences were found between treatments for serum free-fatty-acid concentrations, plasma lactate concentrations, serum cortisol concentrations, heart rate, and rating of perceived exertion. Thus, a moderate dose of caffeine resulted in more total weight lifted for the chest press and a greater peak power attained during the Wingate test in competitive athletes.
Kathleen Woolf, Wendy K. Bidwell and Amanda G. Carlson
Kathleen Woolf, Megan M. St. Thomas, Nicole Hahn, Linda A. Vaughan, Amanda G. Carlson and Pamela Hinton
This study examined iron status and nutrient intake in highly active (n = 28; 20 ± 2 yr, ≥12 hr purposeful physical activity per week [PPA/wk]) and sedentary (n = 28; 24 ± 3 yr, ≤2 hr PPA/wk) women. Participants completed a 7-day weighed-food record (energy, protein, fiber, alcohol, and micronutrients), 7-day pedometer/activity log, and fasting blood draw (hemoglobin, hematocrit, red blood cell indices, C-reactive protein, serum iron, percent transferrin saturation, total iron-binding capacity, ferritin, transferrin receptor [sTfR], and sTfR index). Independent-sample t tests and the Mann–Whitney nonparametric test compared mean values between groups. Lower serum ferritin (p = .01) and mean cell hemoglobin (p < .01) concentrations were found in active than in sedentary women. Higher mean sTfR (p = .01) and sTfR index (p < .01) values were found in the active women. No significant differences were found between groups for the other blood markers. Serum ferritin concentrations (storage iron) indicated iron depletion (Stage I) in 21% of active and 18% of sedentary participants. Nonetheless, 50% of active and 18% of sedentary participants were iron depleted as evidenced by the sTfR index (ratio of functional-to-storage iron). Elevated sTfR concentrations (functional iron) were observed in 25% of active and 3% of sedentary participants. Although the active women reported greater iron (p < .01) but similar heme iron intakes, they had higher mean sTfR, higher sTfR index, and lower serum ferritin concentrations than the sedentary women. Assessment of iron status may require measures not commonly used in routine assessments.