Carbohydrate ingestion and muscle glycogen depletion during marathon and ultramarathon racing

Two studies were undertaken to characterize the effects of carbohydrate ingestion on fuel/hormone response to exercise and muscle glycogen utilization during prolonged competitive exercise. In study 1, eighteen subjects were divided into three groups, matched for maximum oxygen consumption (VO2max) and blood lactate turnpoint. All subjects underwent a 3-day carbohydrate (CHO) depletion phase, followed by 3 days of CHO loading (500-600 g.day-1). During the race, the groups drank either 2% glucose (G), 8% glucose polymer (GP), or 8% fructose (F). Muscle biopsies were performed before and after the race and venous blood was sampled before and at regular intervals during the race. In study 2, eighteen subjects divided into 2 matched groups ingested either a 4% G or 10% GP solution during a 56 km race. Despite significantly greater CHO ingestion by GP and F in study 1 and by GP in study 2, blood glucose, free fatty acids and insulin concentrations, muscle glycogen utilization and running performance were not different between groups. These studies show (i) that hypoglycaemia is uncommon in athletes competing in races of up to 56 km provided they CHO-load before and ingest a minimum of 10 g CHO.h-1 during competition; (ii) that neither the amount (10 g vs 40 g.h-1) nor the type of carbohydrate (G vs GP vs F) has any effect on the extent of muscle glycogen depletion or running performance in matched subjects racing over distances up to 56 km.

Vitamin and mineral supplementation: effect on the running performance of trained athletes

There is limited scientific justification for the widespread use of vitamin and mineral supplements by athletes. We used a 9-mo, placebo-controlled crossover study design to determine whether a multivitamin and mineral supplement influenced the athletic performance of 30 competitive male athletes. At 0, 3, 6, and 9 mo the runners performed a progressive treadmill test to volitional exhaustion for measurement of maximal oxygen consumption, peak running speed, blood lactate turnpoint, and peak postexercise blood lactate level. Running time in a 15 km time trial was also measured. None of these variables was influenced by 3 mo of active supplementation. We conclude that 3 mo of multivitamin and mineral supplementation was without any measurable ergogenic effect.

The danger of an inadequate water intake during prolonged exercise. A novel concept re-visited

To prevent thermal injuries during distance running, the American College of Sports Medicine proposes that between 0.83 and 1.65 l of water should be ingested each hour during prolonged exercise. Yet such high rates of fluid intake have been reported to cause water intoxication. To establish the freely-chosen rates of fluid intake during prolonged competitive exercise, we measured fluid intake during, body weight before and after, and rectal temperature after competition in a total of 102 runners and 91 canoeists competing in events lasting from 170-340 min. Fluid intakes during competition ranged from 0.29-0.62 l.h-1; rates of water loss ranged from 0.69-1.27 l.h-1 in the runners; values were lower in the canoeists. Mean post-race rectal temperatures ranged from 38.0-39.0 degrees C. There was no relationship between the degree of dehydration and post-race rectal temperature. We conclude that hyperthermia is uncommon in prolonged competitive events held in mild environmental conditions, and that exercise intensity, not the level of dehydration, is probably the most important factor determining the postexercise rectal temperature. During prolonged exercise in mild environmental conditions, a fluid intake of 0.5 l.h-1 will prevent significant dehydration in the majority of athletes.

The effects of ankle guards and taping on joint motion before, during, and after a squash match

The effects of ankle guards and taping on joint motion before, during, and after exercise were studied. Twelve league squash players played two matches, each lasting 1 hour. Two different ankle guards, and two types of tape applied by the same method, served as supports. A specially designed goniometer with electronic digital display (accuracy 1 degree) was used to determine joint range of motion: plantar-flexion and dorsiflexion, neutral inversion and eversion, plantar-flexed inversion and eversion. The results were statistically analyzed to determine the significance of the restriction provided by the supports. This revealed that the two ankle guards provided no significant support. The two tapes, however, provided significant support before exercise and after 10 minutes but not after 1 hour of exercise. Nonelastic (zinc oxide) tape proved to be the most restrictive at all times measured, especially prior to exercise, when the ankle's range of motion was decreased between 30% and 50%. However, once exercise commenced, the tape stretched, and restriction became less effective.