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Y Epstein

Publications and source records attributed to Y Epstein.

At least 73 records · Page 4Linked to original sources
PubMed1991

The effects of glucose polymer beverage ingestion during prolonged outdoor exercise in the heat.

The aim of this study was to examine the effect of ingestion of a glucose polymer drink on fluid and metabolic balance during a 30 km outdoor march in the heat (ambient temperature, 26-31 degrees C; relative humidity, 53-34%). The subjects were randomly assigned to one of three groups: 7.2% glucose polymer-electrolyte beverage (GP) (N = 16), flavored sweetened placebo drink (SP) (N = 15), and tap water (TW) (N = 18). The subjects in the three groups consumed similar volumes of fluid, and no differences were found in sweat rate and percent dehydration. Changes in plasma volume were smaller, though not statistically significant, for GP than for SP and TW (-2.8%, -5.4%, -9.4%, respectively). Changes in sodium concentrations and serum osmolality were similar in the three groups. Subjects consuming GP maintained during exercise a significantly higher (P less than 0.001) blood glucose concentration (range: 6.5-7.4 mmol.l-1) than the SP and TW groups. They were also found to have increased levels of serum insulin (29.3 +/- 18.5 mU.l-1) and no change in serum free fatty acids (0.52 +/- 0.19 mmol.l-1). In contrast, subjects ingesting SP or TW had significantly elevated (P less than 0.001) concentrations of free fatty acids (range: 1.35-1.74 mmol.l-1) compared with subjects consuming GP (0.35-0.52 mmol.l-1), with no significant change in blood glucose and serum insulin levels over the exercise period. We conclude that highly trained endurance athletes may maintain a higher blood glucose level by consuming GP during prolonged exercise in the heat without impairing fluid replacement.

Adult↗
PubMed1990

Effect of pyridostigmine on the exercise-heat response of man.

The effect of pyridostigmine on thermoregulatory responses was evaluated during exercise and heat stress. Eight heat acclimated, young adult male subjects received four doses of pyridostigmine (30 mg) or identical placebo tablets every 8 h, in a double blind, randomized, cross-over trial. A 30.3%, SD 4.6% inhibition of the circulating cholinesterase (ChE) activity was induced in the pyridostigmine-treated group. The subjects were exposed to 170-min exercise and heat-stress (dry bulb temperature, 33 degrees C; relative humidity 60%) consisting of 60 min in a sitting position and two bouts of 50-min walking (1.39 m.s-1, 5% gradient) which were separated by 10-min rest periods. No differences were found between treatments in the physiological responses and heat balance parameters at the end of exposure: heart rate (fc) was 141 beats.min-1, SD 16 and 150 beats.min-1, SD 12, rectal temperature (Tre) was 38.5 degrees C, SD 0.4 degrees and 38.6 degrees C, SD 0.3 degrees, heat storage was 60 W.m-2, SD 16 and 59 W.m-2, SD 15 and sweat rate was 678 g.h-1, SD 184 and 661 g.h-1, SD 133, in the pyridostigmine and placebo treatments, respectively. The changes in Tre and fc over the heat-exercise period were parallel in both study and control groups. Pyridostigmine caused a slight slowing of fc (5 beats.min-1) which was consistent throughout the entire exposure (P less than 0.001) but was of no clinical significance. The overall change in fc was similar for both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Lipid profile in trained subjects undergoing complete food deprivation combined with prolonged intermittent exercise.

Sixteen male subjects [18-21 years, maximal oxygen consumption (VO2max) = 59.2 ml.kg-1.min-1 +/- SEM 5.6] participated in a study to evaluate the effect of prolonged, complete food deprivation combined with physical effort, on plasma lipoprotein concentrations. The subjects were deprived of food for 81 h but were supplied with water: they walked for 10 h a day at 40% of VO2max, covering a total of 105 km. During this period the subjects' average mass decreased significantly (P less than 0.05) reflecting a marked catabolic process. Plasma concentration of low density lipoprotein-cholesterol [( LDL-C]) and triglycerides were significantly lower (P less than 0.05) and total cholesterol, high-density lipoprotein-cholesterol [( HDL-C]), and free fatty acid levels were significantly higher (P less than 0.05) at the end of the experimental period compared to the start. The ratio between plasma [HDL-C] to plasma [LDL-C] increased from 0.51 to 0.89 at the end of the exercise period, reflecting a marked anti-atherogenic effect. All changes were transient and reversible within 12 days of recovery.

Adolescent↗
PubMed1990

Androgenic response to long-term physical training in male subjects.

An increase in endogenous androgen production has been observed following long-term physical training and the beneficial effects of training have been attributed in part to this phenomenon. Other investigators, however, found, in contrast lower testosterone levels in trained compared with untrained subjects. The purpose of the present study was to follow the long-term changes in total testosterone (T) and cortisol (C) levels in intensely training individuals. The changes in the body's anabolic state, induced by intense long-term physical training, were determined using the plasma resting T/C ratio. T and C levels of 35 young untrained subjects were measured at 6 week intervals during 18 weeks of strenuous physical training. All samples were drawn within one half hour of awaking (05.30-06.00). Mean serum T levels increased significantly at 6 weeks (28.7%, p less than 0.02) and decreased significantly at 12 weeks (20.6%, p less than 0.02), but did not differ at 18 weeks compared with levels before training was commenced (mean +/- SE, 16.9 +/- 0.2, 21.8 +/- 0.3, 12.8 +/- 0.2 and 17.3 +/- 0.2 nmol/l at 0, 6, 12, and 18 weeks, respectively). Mean serum C was increased significantly (21.3%, p less than 0.005) at 18 weeks (463.5 +/- 19.3, 507.7 +/- 22.1, 480.1 +/- 19.3, and 565.6 +/- 22.1 nmol/l). T/C ratio decreased significantly after 12 and 18 weeks of training. Our results do not support an association between reduced total testosterone levels and prolonged training. However, hypercorticolism with a relative catabolic state may occur.

Adaptation, Physiological↗
PubMed1990

Effect of an acute bout of exercise on glucose disposal in human obesity.

The effect of acute exercise on insulin action has been studied in six obese (150-250% ideal body weight) non-insulin-dependent diabetics (OD), seven obese normoglycemics (ON), and six lean healthy controls (LC). Using a three-stage euglycemic clamp, the metabolic clearance rate (MCR) of glucose under increasing insulin concentrations was measured. The insulin dose-response curve was assessed on two separate occasions: 1) a base-line test and 2) 1 h after aerobic treadmill exercise at a steady-state heart rate of 150-160 beats/min. In the base-line test, under all insulin levels, glucose MCR was significantly lower in obese compared with lean individuals (P less than 0.01). Exercise increased glucose MCR at the highest hormonal concentrations applied to 124 and 134% of base line in OD and in ON, respectively (P less than 0.05); the insulin concentration required for one-half of the maximal clearance rate of glucose achieved in this study decreased from 200 to 130 and from 160 to 95 microU/ml in OD and ON, respectively (P less than 0.05). The changes in these parameters were insignificant in LC. It is suggested that acute exercise affected the insulin dose-response curve in OD and in ON but not in LC; although enhanced by exercise, glucose MCR remained significantly lower in both obese groups compared with control subjects. We concluded that insulin resistance, which accompanies extreme obesity, could be markedly decreased but not completely reversed by one bout of exercise.

Adult↗
PubMed1990

Heat-exercise performance of pyridostigmine-treated subjects wearing chemical protective clothing.

Pyridostigmine bromide is currently the pretreatment of choice for operation in a chemical warfare (CW) environment. Under CW conditions, subjects are exposed to thermal stress caused by CW protective clothing. This investigation was conducted to determine if pyridostigmine affects various physiological and biophysical parameters of human temperature regulation in subjects wearing CW protective clothing. Pyridostigmine was administered orally in a randomized double-blind cross-over study in four doses of 30 mg every 8 h. An average of 33% whole blood cholinesterase inhibition was induced in the pyridostigmine treated group 4 h after ingestion of last tablet. The subjects were exposed to 170 min exercise-heat stress (Tdb = 33 degrees C; rh = 60%) consisting of 60 min in a sitting position and two 50-min walks (1.39 m.s-1, 5% grade) separated by 10 min of rest. Non-evaporative heat exchange was significantly higher, -14.0 and -10.6 W.m-2 (p less than 0.03), for the pyridostigmine-treated subjects. No additional differences were found between treatments in the physiological responses and heat balance parameters at the end of exposure: heart rate (HR) was (mean +/- S.D.) 154 +/- 16 and 151 +/- 24 bpm, rectal temperature (Tre) was 39.0 +/- 0.4 and 38.9 +/- 0.2 degrees C, heat storage over the 2 h of exercise was 62 +/- 15 and 70 +/- 15 W.m-2, and sweat rate was 832 +/- 185 and 748 +/- 52 g.h-1, in the pyridostigmine and placebo treatments, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Familial generalized anhidrosis.

A young Caucasian male, otherwise healthy, had had generalized anhidrosis since early childhood. During heat stress tests (40 degrees C, 40% relative humidity), he was found to be heat intolerant since sweat was not apparent. His reaction to muscarinic stimulation of sweat glands was 10% of normal. On biopsy, the sweat glands were morphologically intact, and function of his cardiovascular autonomic responses was normal. The patient's mother reported reduced sweating and her response to muscarinic stimulation was 50% of normal, but his father and both sisters sweated normally. The data suggest a post-ganglionic defect, which may be genetic. To our knowledge this is the first reported case of familial generalized anhidrosis without anatomopathological lesions affecting sweat glands.

Adolescent↗
PubMed1990

Heat intolerance: predisposing factor or residual injury?

Great individual variability exists in the ability to sustain heat stress. Some individuals are more susceptible to heat than others. Those individuals, among the young active population (athletes, military recruits, laborers), are at risk to contract exertional heat stroke. Low tolerance to heat results from either functional factors, or from congenital or acquired disturbances. In most cases heat intolerance can be foreseen. Cases of dehydration, overweight, low physical fitness, lack of acclimatization, febrile or infectious diseases, and skin disorders should be regarded a priori as predisposing factors for heat intolerance. Special attention should be paid to subjects with previous heat stroke episodes since it might reflect an underlying cause for heat susceptibility. The heat tolerance of these subjects should be tested 8-12 wk postepisode to detect a possible residual injury in the ability to thermoregulate adequately in the heat.

Acclimatization↗
PubMed1989

[Physiological responses to heat and effort and complaints of hyperperspiration].

The sensation of hyperperspiration is a common complaint in hot, humid climates. 54 men and 20 women, 18-47 years old, who had this complaint and 27 male control subjects were examined at rest and after 1 hour of mild exercise (40W) under conditions of heat stress (37 degrees C, 50% relative humidity). During exposure to heat rectal and skin temperatures and heart rate were measured every 15 min. Sweat rate was calculated for the entire period of exposure and sweat gland density was measured at 0, 60 and 120 min. Only insignificant deviations from baseline values were noted at rest. During exercise the sweat rate of the men with the complaint was within normal limits and similar to that of the control men (285 +/- 75 ml/m2 vs 272 +/- 48). Matching for age and V02 max revealed no significant differences in physiological responses of men with and those without the complaint. Women with the complaint lost 25-30% less fluid (226 +/- 67 ml/m2) and their concentrations of active sweat glands were lower than in either of the male groups. 2 men and 1 woman with the complaint and 1 control lost 400-425 ml/m2 during exercise, the upper limit of normal. Only 1 subject showed hyperperspiration (855 ml/m2) during the test. All physiological parameters examined in these 5 subjects were within normal limits. It is concluded that the complaint of hyperperspiration in our self-selected group is basically a subjective feeling and has no pathological basis. None of the subjects was heat intolerant.

Adult↗
PubMed1989

Plasma-cortisol levels in experimental heatstroke in dogs.

The effect of external heat-load, exercise and dehydration on dynamic changes in plasma cortisol during the development of heatstroke was investigated. Thirty-three unanesthetized dogs were tested under two sets of climatic conditions: comfort conditions and hot-dry climatic conditions, half of them while exercising. Half of the dogs in each group were rehydrated. None of the dogs that were investigated at room temperature suffered heatstroke. Of the dogs exposed to high ambient temperature, all of the exercising, as well as five out of six non-hydrated dogs and one rehydrated non-exercising dog suffered heatstroke. Significant dehydration (6%-7% of body weight), occurred only under high ambient temperature. Plasma cortisol levels of all dogs that suffered heatstroke rose conspicuously for at least 5 h and returned to normal levels 24 h later. Cortisol levels of dogs who did not experience heatstroke remained within the normal range. Cortisol levels correlated with the severity of the stress leading to heatstroke. High and rising levels of cortisol, several hours after body temperature returns to normal, may support the diagnosis of heatstroke.

Animals↗
PubMed1988

Prediction of physical performance through muscle enzymes activity.

Physical performance deteriorates during strenuous exercise as manifested by a decrease in maximal aerobic power and increased activity of serum muscle enzymes. The relationship between these parameters was investigated in 41 trained subjects during 24 h marches and the following recovery period. Peak O2 uptake and serum activity of creatine phosphokinase (CPK) and glutamic oxalacetic transaminase (GOT) were measured. During the marches there was a simultaneous, significant elevation in serum CPK and GOT activity and a significant reduction in peak O2 uptake. During the early recovery period (24 h) no significant changes occurred in muscle enzyme activity and peak O2 uptake; thereafter (up to 72 h after the end of the march), a gradual decline in enzyme activity levels with a concomitant increase in peak O2 uptake was observed, reaching pre-march values. A "mirror image" relationship between muscle enzyme activity and peak O2 uptake was found during three clearly distinguished phases: a) 24 h march, b) early recovery stage and c) late recovery stage. These findings suggest that muscle enzyme leakage from muscle cells is closely related to the decline in muscular function and aerobic power. Thus, muscle enzyme activity might be a practical measure of physical performance capacity during the early and late stages of recovery from prolonged endurance exercise.

Adult↗
PubMed1988

External load can alter the energy cost of prolonged exercise.

The present study was undertaken to examine the energy cost of prolonged walking while carrying a backpack load. Six trained subjects were tested while walking for 120 min on a treadmill at a speed of 1.25 m.s-1 and 5% elevation with a well fitted backpack load of 25 and 40 kg alternately. Carrying 40 kg elicited a significantly higher (p less than 0.01) energy cost than 25 kg. Furthermore, whereas carrying 25 kg resulted in a constant energy cost, 40 kg yielded a highly significant (p less than 0.05) increase in energy cost over time. The study implies that increase in load causes physical fatigue, once work intensity is higher than 50% maximal work capacity. This is probably due to altered locomotion biomechanics which in turn lead to the increase in energy cost. Finally, the prediction model which estimates energy cost while carrying loads should be used with some caution when applied to heavy loads and long duration of exercise, since it might underestimate the actual energy cost.

Adult↗