Search Results

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, ${\text{B}}_6$ , ${\text{B}}_{12}$ , and E. Biochemical evidence of vitamin deficiencies in some athletes have been reported for thiamine, riboflavin, and ${\text{B}}_6$ . When the diet is deficient, vitamin supplements may improve performance but are not likely to be effective if the dietary intake is adequate. Some female athletes' diets are low in calcium, iron, and zinc. Low calcium intake may reduce peak bone mass in young women. Iron deficiency may impair performance and needs to be corrected with an iron supplement. Zinc supplements that exceed the RDA interfere with the absorption of copper and lower HDL-cholesterol.

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.

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.

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 ${\text{VO}}_2\max$ and an endurance test (80% ${\text{VO}}_2\max$ ) on a cycle ergometer. The low femtin group had significantly lower serum iron concentration and transferrin saturation and higher TIBC than the normal femtin group. Mean ${\text{VO}}_2\max$ was not significantly different between groups. No significant difference was found in total time to exhaustion during the endurance test for low (23.2 min) and normal (27.0 min) femtin groups; however, the normal femtin group exercised 14% longer. Blood lactate concentrations following the VOzmax and endurance test did not differ significantly between groups. Food diaries revealed lower daily absorbable iron intake by the low femtin group compared to the normal ferritin group. Ferritin concentration was significantly related to absorbable iron (r=.72) and total iron (r=.70) intake. The results suggest that women with depleted iron stores who are not anemic may have less endurance, but do not have higher blood lactate during exercise than women with normal iron stores.

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% ${\text{VO}}_2\max$ ) and moderate (50% ${\text{VO}}_2\max$ ) aerobic intensities in eight sedentary ( ${\text{VO}}_2\max$ 39.6 ±t3.1 ml.kg⁻¹.min⁻¹) males. Caffeine intake 60 min prior to walking exercise increased pre- and postexercise FFA, glycerol, and lactate concentrations (p < 0.05). Blood glucose levels following walking trials were lower than preexercise values (p < 0.05). Gas exchange indicated that caffeine did not change exercise oxygen uptake, RER values, and carbon dioxide production (p0.05). In contrast, a small but statistically significant effect of caffeine on exercise minute ventilation was noted (p~0.01). It is concluded that ingestion of 5 mg.kg⁻¹ caffeine increases the mobilization of energy substrate from fat sources; however, the present data do not provide evidence of a caffeineinduced shift in energy substrate usage. Caffeine is not an effective means for enhancing the energy cost of prolonged walking.

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 ${\text{O}}_2$ cost were measured. The time to exhaustion was significantly longer during the caffeine trial than during the placebo trial. Serum free fatty acid levels were significantly different between trials. The decline in blood glucose levels was significantly less during the caffeine trial than during the placebo trial. There were no significant differences between trials for the other measures. It was concluded that caffeine increases time to exhaustion when trained subjects cycled intermittently at high levels of intensity.