Flattened cola improves high-intensity interval performance in competitive cyclists.

PURPOSE: Some cyclists consume flattened cola during competitive events, but limited research has investigated if cola beverages elicit ergogenic effects, particularly on high-intensity exercise performance. Whether the potentially beneficial effects of cola are due to the caffeine and/or the carbohydrate content is also unclear. This study assessed the ergogenic effects of different cola beverages on performance during a constant power bout (CPB) and subsequent high-intensity interval efforts in competitive cyclists. METHODS: In a randomized, double-blind, cross-over design, competitive cyclists (n = 13; [Formula: see text]O2max 65.7 ± 5.9 ml kg-1 min-1) completed a 45-min CPB at 69% of maximum workload (Wmax), followed by four maximal 1-min high-intensity intervals (HII) against a resistance of 0.5 N kg-1. Participants consumed 16 ml kg-1 total (intermittantly at four time points) of flattened decaffinated diet cola (PLA), caffeinated diet cola (CAF) or cola containing caffeine and carbohydrates (CAF + CHO). RESULTS: During the CPB, ratings of perceived exertion were lower in the CAF + CHO and CAF conditions compared to PLA (both, P < 0.04). Compared to PLA, CAF + CHO and CAF similarly increased (all, P < 0.049) mean power (CAF + CHO: 448 ± 51 W; CAF: 448 ± 50 W; PLA: 434 ± 57 W), minimum power (CAF + CHO: 353 ± 45 W; CAF: 352 ± 51 W; PLA: 324 ± 49 W) and total work (CAF + CHO: 26.9 ± 3.1 kJ; CAF: 26.9 ± 3.0 kJ; PLA: 26.0 ± 3.4 kJ), but not peak power (CAF + CHO: 692 ± 117 W; CAF: 674 ± 114 W; PLA: 670 ± 113 W; all, P > 0.57) during the HII. CONCLUSION: Cola containing caffeine with or without carbohydrates favorably influenced perceived effort during the CPB and enhanced mean and minimum power during repeated maximal intervals. We provide evidence supporting the consumption of commercially available cola for high-intensity cycling in competitive cyclists.

Urine specific gravity in exercisers prior to physical training.

Urine specific gravity (USG) is used as an index of hydration status. Many studies have used USG to estimate pre-exercise hydration in athletes. However, very little is known about the pre-exercise hydration status of recreational exercisers. The purpose of the present study was to measure the pre-exercise USG in a large sample of recreational exercisers who attended 2 different fitness centers in the United States. In addition, we wanted to determine if factors such as time of day, geographic location, and gender influenced USG. We tested 166 subjects in Chicago and 163 subjects in Los Angeles. Subjects completed a survey on their typical training regimen and fluid-replacement habits, and thereafter voided and delivered a urine sample to the investigators prior to beginning exercise. Samples were measured on site for USG using a hand-held refractometer. The mean (SD) USG was 1.018 (+/- 0.007) for all subjects. Males had a higher average USG (1.020 +/- 0.007) when compared with females (1.017 +/- 0.008; p = 0.001). Despite differences in climate, no difference in mean USG occurred based on location or time of day. Based on standards used for athletes (USG > or = 1.020), 46% of the exercisers were likely to be dehydrated.

Caffeine ingestion increases the insulin response to an oral-glucose-tolerance test in obese men before and after weight loss.

BACKGROUND: Caffeine ingestion decreases the insulin sensitivity index (ISI) for an oral-glucose-tolerance test (OGTT) and decreases insulin-induced glucose disposal in lean male subjects during a hyperinsulinemic clamp. OBJECTIVE: We examined the effects of caffeine ingestion on insulin and glucose homeostasis in obese men before and after a nutrition and exercise intervention. DESIGN: Nine sedentary, obese [body mass index (in kg/m(2)): 34.0 +/- 1.0] men who had refrained from exercise and caffeine ingestion for 48 h underwent 2 oral-glucose-tolerance tests (OGTTs). The subjects randomly received caffeine (5 mg/kg) or placebo 1 h before each OGTT. After a 12-wk nutrition and exercise intervention, during which time the subjects avoided dietary caffeine, the OGTTs were repeated. RESULTS: The intervention resulted in decreases (P < or = 0.05) in body weight (8.5 +/- 1.5 kg), percentage body fat (2.8 +/- 0.7%), and fasting glucose, insulin, and proinsulin concentrations and increases in the ISI for the placebo OGTT (P < or = 0.05). Caffeine caused a greater (P < or = 0.05) OGTT insulin response and a lower (P < or = 0.05) ISI both before and after weight loss. The proinsulin-insulin ratio indicated that neither weight loss nor caffeine affected the nature of the beta cell secretion of insulin. CONCLUSIONS: A nutrition and exercise intervention improved, whereas caffeine ingestion impaired, insulin-glucose homeostasis in obese men. The results are consistent with previous findings that caffeine ingestion contributes to insulin resistance.

Nutritional concerns for the child and adolescent competitor.

With exercise for sports competition in children and adolescents, acute nutrient needs will change. Fluid intake to ensure the replacement of water and minerals (electrolytes) lost in sweat is important. Energy needs also increase because of the elevated energy expenditure with physical activity. Arguably carbohydrate is the recommended source of training needs, although research has yet to be done to show performance benefits in young athletes on a high-carbohydrate diet. In the majority of sports, an increased intake of food naturally occurs to accommodate the day-to-day nutrient needs of young athletes, and unlike non-athlete, young competitors typically come closer to meeting their requirements for micronutrients. Nonetheless, certain athletic groups may be at risk for shortfalls in their diet. Compared to athletes in team sports, participants in weight-control sports may be at greater risk of failing to meet requirements for energy, protein, and some micronutrients. Endurance athletes, particularly female distance runners, may have intake deficits for the minerals iron and calcium. Acute issues such as heat illness and chronic concerns that include impaired growth and development, and the risk of injuries that include stress fractures may be an outcome of inadequate nutrition during physical training.