Marvin L. Riedesel

Effects of glycerol-induced hyperhydration prior to exercise in the heat on sweating and core temperature

Hypohydration reduces exercise performance and thermoregulatory capacity in the heat. Hyperhydration prior to exercise may decrease, delay, or eliminate the detrimental effects of hypohydration. The rapid clearance of excess fluid makes hyperhydration of subjects with common beverages difficult. Glycerol, a natural metabolite which is rapidly absorbed, has osmotic action, and is evenly distributed within the body fluid compartments, was tested as a possible hyperhydrating agent. In six subjects, the following fluid regimens at time 0 were randomly administered on three separate days: in trial 1, glycerol (1 g.kg-1 body weight) plus water (21.4 ml.kg-1 body weight); in trial 2, water (21.4 ml.kg-1); and in trial 3, water (3.3 ml.kg-1) was ingested at time 0. The subjects performed moderate exercise (equivalent to 60% VO2max in a comfortable environment) in a hot dry environment. The exercise started at 2.5 h after the fluids were ingested. The urine volume prior to exercise was decreased when glycerol was ingested, thus resulting in glycerol-induced hyperhydration. During the exercise following the glycerol-induced hyperhydration, there was elevated sweat rate and lower rectal temperature during the moderate exercise in the heat. There were no changes in hemoglobin, hematocrit, or serum electrolyte concentrations following glycerol intake. These data support the hypothesis that glycerol-induced hyperhydration reduces the thermal burden of moderate exercise in the heat.

Body composition of oligo/amenorrheic athletes

Menstrual dysfunction in athletes may be related to low body weight or low body fat content. To investigate the relationship between body composition and menstrual function, body composition was evaluated by hydrostatic weighing in two groups of women: 14 athletes with oligo/amenorrhea and 28 athletes with regular menstruation. Age and height were similar in the two groups. In all of the weight parameters, including total body weight, percent ideal body weight, Livi Index, percent body fat, fat weight, and lean body weight, athletes with oligo/amenorrhea were significantly lighter than athletes with regular menstruation. We concluded that menstrual dysfunction in athletes is associated with low body weight, which is comprised of smaller amounts of both fat and lean body mass.

SUSTAINED HYPERHYDRATION WITH GLYCEROL INGESTION

Heavy exercise lasting more than three hours tends to result in dehydration, as the fluid intake is less than fluid loss by sweat and urine. Dehydration as small as one percent of body weight has been reported to decrease work capacity. In present and previous studies insensible water loss and sweat are assumed to be the same in both control and experimental conditions. Fluid intake less urine volume is utilized as an indicator of euhydration, hypohydration, or hyperhydration. Previous studies involving glycerol intake describe hyperhydration for 4.5 to 8 hours. The objective of this study was to keep subjects hyperhydrated (retention of water) for 32 or 49 hours. The experimental protocol involved ingestion of a large volume of fluid (39.2 or 51.1 ml/kg/d) with glycerol (2.9 to 3.1 g/kg/d) and without glycerol. In both Series I (49 h) and Series II (32 h) experiments, the intake of glycerol resulted in smaller urine volumes. This study demonstrates it is possible to keep human subjects hyperhydrated for extended periods of time and thereby reduce the amount of fluid consumption necessary just prior to or during bouts of negative fluid balance situations.

A survey of menstrual function in athletes

SummaryQuestionnaires were given to 254 female athletes and 426 nonathletic control subjects, and interviews were conducted with 95 athletes. Menstrual characteristics in the two groups were strikingly different, with oligo/amenorrhea reported by 12.1% of the athletes and 2.6% of the control subjects, and regular menstruation reported by 42.9% of the athletes and 64.3% of the control subjects. About half the athletes interviewed were able to cite specific changes in their menstruation that were associated with specific changes in their athletic training. Low body weight was the factor most commonly associated with oligo/amenorrhea in athletes, but among the control subjects menstrual characteristics did not appear to be influenced by body weight. Lighter oligo/amenorrheic athletes reported more severe menstrual disturbances than heavier oligo/amenorrheic athletes. Distance runners reported fewer menstrual periods per year than other athletes, and weekly training distance appeared to influence menstrual characteristics among the runners. Other factors which appeared to be associated with athletic oligo/amenorrhea included a vegetarian diet and a high altitude environment. We conclude that menstrual disturbances are often associated with athletic training, and that several factors, particularly low body weight, can increase susceptibility to exercise-related oligo/amenorrhea.

Memory and Hibernation in Citellus lateralis

Squirrels learned to escape from a water bath by making a visual discrimination. Twenty-four hours after reaching criterion for learned behavior, the animals were exposed to the first of two 11-day cold exposures. The animals that hibernated had better retention of the learned behavior.

Respiratory responses to long-term temperature exposure in the box turtle,Terrapene ornata

SummaryIn late February, seven box turtles were collected with body temperatures between 7 and 9°C. Ventilation, gas exchange and end-tidal

Water content of ground squirrel and laboratory rat tissues

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Cs137 metabolism in Blatta orientalis at various temperatures

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