Muscle glycogen is the primary source of energy during high intensity exercise. Increasing the carbohydrate content of the diet allows more glycogen to be stored. Some adolescent female athletes (gymnasts, dancers) do not consume adequate amounts of vitamin B6, folacin, and E. Many women have low dietary intakes of calcium and iron. Low calcium intake and physical inactivity are factors associated with the development of osteoporosis. Low iron intake is associated with the development of iron deficiency and anemia. Low ferritin levels (an index of body iron stores) are commonly observed in female athletes.
Emily M. Haymes
Emily M. Haymes
Vitamin and mineral supplements are frequently used by competitive and recreational athletes. Dietary deficiencies of most vitamins are not very common among athletes except in those who restrict their food intake in order to maintain body weight. Vitamins most likely to be deficient in the diet are folate,
Isaiah Trice and Emily M. Haymes
In this study a double-blind design was used to determine the effect of caffeine on time to exhaustion and on associated metabolic and circulatory measures. Eight male subjects ingested either caffeine (5 mg/kg body weight) or a placebo 1 hr prior to exercise at 85-90% of maximum workload. Subjects were encouraged to complete three 30-min intermittent cycling periods at 70 rpm with 5 min rest between each. The exercise was terminated when the subject failed to complete three 30-min periods or failed to maintain 70 rpm for at least 15 s consecutively. Serum free fatty acids, glycerol, blood glucose, lactate, perceived exertion, heart rate, and
Priscilla M. Clarkson and Emily M. Haymes
This paper reviews information pertaining to zinc, copper, chromium, and selenium requirements of athletes. Exercise increases zinc loss from the body, and dietary intake for some athletes, especially females, may be inadequate. Blood copper levels are altered by exercise, but there is no information to suggest that copper ingestion or status is compromised in athletes. Studies have shown that urinary chromium excretion is increased by exercise, but whether this leads to an increased requirement is still unknown. There is concern that athletes may not ingest sufficient quantities of chromium; however, there are inadequate data to confirm this. The limited data that exist show that athletes do not have altered selenium status. There is no conclusive evidence that supplementation with any of these trace minerals will enhance performance. A diet containing foods rich in micronutrients is recommended. However, for those athletes concerned that their diets may not be sufficient, a multivitamin/ mineral supplement containing no more than the RDA may be advised.
Herman-J. Engels and Emily M. Haymes
This study examined the effects of a single dose of caffeine (5 mg:kg−1) on energy metabolism during 60-min treadmill walking at light (30%
John J. Lamanca and Emily M. Haymes
To determine the effects of depleted iron stores on endurance performance and blood lactate concentration, eight active women with normal (>26 ng/ml) and eight with low (< I2 nglml) plasma ferritin concentrations were studied while performing a
Emily M. Haymes and Ronald J. Maughan
Kevin Tipton, Nancy R. Green, Emily M. Haymes, and Mary Waller
Zinc (Zn) loss from sweat of 9 male and 9 female athletes exercising under hot (35°C, HE) and neutral (25°C, ME) conditions was examined. Subjects exercised at 50% VO2max on a cycle ergometer for 1 hr during each trial. Cell-free sweat samples were analyzed for Zn by atomic absorption spectro-photometry. There was a significant interaction of time, gender, and temperature for whole-body sweat rates (WBSR). WBSR for males were higher during both trials and at each time. WBSR from the second half of exercise were higher than those from the first half for both sexes and temperature conditions. Sweat Zn concentration was higher in the NE than in the HE, but when the sweat rates were included, the rate of Zn loss was no different between HE and NE. Zn concentration of the sweat for the first half of exercise was over twice that of the second half. Sweat Zn concentration of the men was no different than that of the women; however, due to greater sweat rate, men had significantly higher Zn losses. Although total Zn losses are estimated to be relatively low compared to the RDA. exercise at moderate intensities may increase surface Zn losses.
Laurel M. Wentz, Pei-Yang Liu, Jasminka Z. Ilich, and Emily M. Haymes
High rates of vitamin D deficiency have been reported in athletes. The purpose of this study was to evaluate the associations between vitamin D with bone health and parathyroid hormone (PTH) concentrations in female runners who trained at 30.4° degrees north.
Serum 25-hydroxyvitamin D (25(OH) D), PTH, body composition, and bone mineral density (BMD) were measured in 59 female runners, aged 18–40 years. Stress fracture history, training duration and frequency were evaluated by questionnaire. As per National Endocrine Society cut-offs, serum vitamin D ranges were: 25(OH)D < 50 nmol/L for deficient; 50–75 nmol/L for insufficient; and ≥ 75 nmol/L for sufficient status.
Mean serum 25(OH)D concentrations were 122.6 ± 63.9 nmol/L, with 18.6% of subjects in the deficient (5.1%) or insufficient (13.5%) range. No significant differences were observed between sufficient and deficient/insufficient subjects for BMD, PTH, history of stress fractures, or demographic data.
The majority of distance runners maintained sufficient vitamin D status, suggesting that training outdoors in latitude where vitamin D synthesis occurs year-round reduces the risk for vitamin D deficiency. Data do not support the indiscriminate supplementation of outdoor athletes in southern latitudes without prior screening.
Beau Kjerulf Greer, John L. Woodard, Jim P. White, Eric M. Arguello, and Emily M. Haymes
The purpose of this study was to determine whether branched-chain amino acid (BCAA) supplementation attenuates indirect indicators of muscle damage during endurance exercise as compared with an isocaloric, carbohydrate (CHO) beverage or a noncaloric placebo (PLAC) beverage. Nine untrained men performed three 90-min cycling bouts at 55% VO2peak. Subjects, blinded to beverage selection, ingested a total of 200 kcal of energy via the CHO or BCAA beverage before and at 60 min of exercise, or they drank the PLAC beverage. Creatine kinase (CK), lactate dehydrogenase (LDH), isokinetic leg-extension and fexion torque, and muscle soreness were assessed before and immediately, 4 h, 24 h, and 48 h post exercise. The trials were separated by 8 wk. CK activities were significantly lower after the BCAA trial than in the PLAC trial at 4, 24, and 48 h post exercise, as well as lower than the CHO beverage at 24 h post exercise. CK was lower in the CHO trial at the 24- and 48-h time points than in the PLAC trial. LDH activities were lower in the BCAA trial at 4 h than in the PLAC trial. As compared with the CHO and PLAC trials, ratings of perceived soreness were lower at 24 h post exercise, and leg-fexion torque was higher at the 48-h time point after the BCAA trial. The present data suggest that BCAA supplementation attenuates muscle damage during prolonged endurance exercise in untrained college-age men. CHO ingestion attenuates CK activities at 24 and 48 h post exercise as compared with a placebo beverage.