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Biomedical subjects

E M Haymes

Publications and source records attributed to E M Haymes.

At least 19 recordsLinked to original sources
PubMed2001

Ad libitum fluid intakes and thermoregulatory responses of female distance runners in three environments.

Ad libitum fluid intakes and thermoregulatory responses were compared in eight female marathon runners during a 30 km treadmill run at individual best marathon race pace (range = 2.45-4.07 m x s(-1)) under three wet bulb globe temperature conditions (25 degrees C, 17 degrees C and 12 degrees C, corresponding to hot, moderate and cool conditions, respectively). Rectal temperature, mean skin temperature and heart rate were recorded at 10 min intervals and expired air was collected every 5 km during exercise. Simulated water stations were also provided at 5 km intervals with voluntary fluid intake being recorded. Blood was drawn before and after exercise for the determination of plasma volume changes and osmolarity. Ad libitum fluid intakes in the hot trial (0.70+/-0.31 l x h(-1); mean+/-s) were greater (P< 0.05) than in the cool (0.47+/-0.13 l x h(-1)) but not the moderate (0.54+/-0.26 l x h(-1)) trial. Each volume replaced 63%, 68% and 73% of total sweat losses in each condition, respectively, and kept dehydration below approximately 3% of body mass. After the initial 30 min of exercise, rectal temperature was maintained well below 39 degrees C for > 2 h of continuous running. The results demonstrate that the thermoregulatory responses of female distance runners to exercise in variable, but compensable, weather conditions is well maintained when ad libitum fluid intakes replace approximately 60-70% of sweat losses.

Adult↗
PubMed2001

Thermoregulation and marathon running: biological and environmental influences.

The extreme physical endurance demands and varied environmental settings of marathon footraces have provided a unique opportunity to study the limits of human thermoregulation for more than a century. High post-race rectal temperatures (Tre) are commonly and consistently documented in marathon runners, yet a clear divergence of thought surrounds the cause for this observation. A close examination of the literature reveals that this phenomenon is commonly attributed to either biological (dehydration, metabolic rate, gender) or environmental factors. Marathon climatic conditions vary as much as their course topography and can change considerably from year to year and even from start to finish in the same race. The fact that climate can significantly limit temperature regulation and performance is evident from the direct relationship between heat casualties and Wet Bulb Globe Temperature (WBGT), as well as the inverse relationship between record setting race performances and ambient temperatures. However, the usual range of compensable racing environments actually appears to play more of an indirect role in predicting Tre by acting to modulate heat loss and fluid balance. The importance of fluid balance in thermoregulation is well established. Dehydration-mediated perturbations in blood volume and blood flow can compromise exercise heat loss and increase thermal strain. Although progressive dehydration reduces heat dissipation and increases Tre during exercise, the loss of plasma volume contributing to this effect is not always observed for prolonged running and may therefore complicate the predictive influence of dehydration on Tre for marathon running. Metabolic heat production consequent to muscle contraction creates an internal heat load proportional to exercise intensity. The correlation between running speed and Tre, especially over the final stages of a marathon event, is often significant but fails to reliably explain more than a fraction of the variability in post-marathon Tre. Additionally, the submaximal exercise intensities observed throughout 42 km races suggest the need for other synergistic factors or circumstances in explaining this occurrence. There is a paucity of research on women marathon runners. Some biological determinants of exercise thermoregulation, including body mass, surface area-to-mass ratio, sweat rate, and menstrual cycle phase are gender-discrete variables with the potential to alter the exercise-thermoregulatory response to different environments, fluid intake, and exercise metabolism. However, these gender differences appear to be more quantitative than qualitative for most marathon road racing environments.

Body Mass Index↗
PubMed1999

Oxidative stress during a 3.5-hour exposure to 120 kPa(a) PO2 in human divers.

We examined the effect of a prolonged dive on measures of oxidative stress in human divers. Ten subjects, wearing dry suits, completed mental tasks while lying quietly at 4.6 m fresh water for 3.5 h. Subjects (9 male, 1 female) were active, experienced divers ranging in age from 19 to 54 yr. Subjects breathed an enriched air nitrox mixture yielding a P(O2) of approximately 120 kPa(a) for the duration of the dive. Venous blood was drawn before and after the dive for measurements of hemoglobin (Hb), hematocrit (Hct), plasma osmolarity (O(SM)), red blood cell osmotic fragility (Frag), superoxide dismutase activity (SODa), and thiobarbituric acid reactive substances (TBARS). Plasma volume (PV) shifts were calculated from the changes in Hb and Hct. Significant increases in Hb, Hct, Osm, Frag, and TBARS were found along with significant decreases in PV and SODa (P < or = 0.05). We conclude that hyperbaric exposures encountered by technical divers are sufficient to cause significant oxidative stress.

Adult↗
PubMed1997

Energy expenditure estimates of the Caltrac accelerometer for running, race walking, and stepping.

OBJECTIVE: To examine the accuracy of the Caltrac accelerometer for estimating energy expenditure (EE) during three exercise modes. METHODS: A subset of 31 women (mean (SEM) age 22.6 (5) years) as selected from a training study comparing various physiological parameters during race walking, running, and stepping. Subjects each performed mode specific graded exercise tests to peak VO2. Regression equations for VO2 v heart rate (HR) were generated from each individual's test data. EE (kcal and kJ) was estimated for each VO2 value based on the respiratory exchange ratio, and kcal v HR regression equations were generated to predict EE from each subject's HR data (EE-HR). HR in the field was monitored by telemetry, and two Caltrac monitors, one set for EE and one to give counts, were attached to a belt over opposite hips. RESULTS: EE-HR was not significantly different across exercise modes. Caltrac overestimated EE (P < 0.01) in runners (14%) and walkers (19%) but underestimated EE in steppers by about 10% (P = 0.12). CONCLUSIONS: The Caltrac is a reliable instrument but it did not accurately distinguish EE in running, race walking, or stepping in a group of young women.

Acceleration↗
PubMed1996

The effects of heat and exercise on sweat iron loss.

Arm sweat was collected from nine male and nine female athletes sitting in a hot environment (HR, 40 degrees C) and exercising at 50% VO2max in neutral (NE, 25 degrees C) and hot (HE, 35 degrees C) environments to compare sweat iron concentrations and losses. Whole body sweat rate was determined from weight loss at 30-min intervals for 1 h. Sweat iron concentration was significantly higher during HR and NE than during HE, but was not significantly different between males and females. During exercise, sweat iron concentration decreased significantly from 30 to 60 min. Whole body sweat rates differed significantly across all environments with the highest rate in HE and the lowest in HR. Males lost significantly more sweat during exercise than females, but the difference at rest was not significant. Estimated whole body iron loss was significantly greater during exercise (NE = 0.08 mg.m-2.h-1, HE = 0.077 mg.m-2.h-1) than rest (0.039 mg.m-2.h-1), and the average iron loss was significantly greater in males (0.09 mg.m-2.h-1) than females (0.04 mg.m-2.h-1). Results suggest that the use of resting sweat iron concentration to estimate iron loss for 1 h of exercise in neutral environments is accurate but may overestimate iron loss during exercise in hot environments and during more prolonged exercise.

Adult↗
PubMed1996

American College of Sports Medicine position stand. Heat and cold illnesses during distance running.

Many recreational and elite runners participate in distance races each year. When these events are conducted in hot or cold conditions, the risk of environmental illness increases. However, exertional hyperthermia, hypothermia, dehydration, and other related problems may be minimized with pre-event education and preparation. This position stand provides recommendations for the medical director and other race officials in the following areas: scheduling; organizing personnel, facilities, supplies, equipment, and communication; providing competitor education; measuring environmental stress; providing fluids; and avoiding potential legal liabilities. This document also describes the predisposing conditions, recognition, and treatment of the four most common environmental illnesses: heat exhaustion, heatstroke, hypothermia, and frostbite. The objectives of this position stand are: 1) To educate distance running event officials and participants about the most common forms of environmental illness including predisposing conditions, warning signs, susceptibility, and incidence reduction. 2) To advise race officials of their legal responsibilities and potential liability with regard to event safety and injury prevention. 3) To recommend that race officials consult local weather archives and plan events at times likely to be of low environmental stress to minimize detrimental effects on participants. 4) To encourage race officials to warn participants about environmental stress on race day and its implications for heat and cold illness. 5) To inform race officials of preventive actions that may reduce debilitation and environmental illness. 6) To describe the personnel, equipment, and supplies necessary to reduce and treat cases of collapse and environmental illness.

Frostbite↗
PubMed1995

Effects of caffeine ingestion on exercise-induced changes during high-intensity, intermittent exercise.

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 O2 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.

Adult↗
PubMed1995

Exercise duration and thermoregulatory responses after whole body precooling.

Whole body precooling was hypothesized to reduce thermoregulatory and metabolic responses, thereby enhancing running time. Fourteen male runners completed two high-intensity running tests consisting of resting in 24 degrees C (normothermic condition; NC) or 5 degrees C (hypothermic condition; HC) for 30 min followed by 10-16 min of rest at 24 degrees C and then an exercise bout (24 degrees C) at 82% maximal aerobic capacity to exhaustion. Rectal temperature (Tre) before exercise was lower (by 0.37 degrees C; P < 0.005) and exercise duration was longer (by 121 +/- 24%; P < 0.05) in HC than in NC. Tre and mean skin (Tsk) and mean body (Tb) temperatures remained lower during HC (P < 0.01). Pre- and postexercise changes for Tsk, Tb, thermal gradient (Tre-Tsk), and heart rate (HR) were larger in HC than in NC (P < 0.05). Final Tre, Tre-Tsk, HR, and blood lactate were similar between HC and NC. During exercise, heat storage was greater (P < 0.01) in HC than in NC (173 +/- 46 and 143 +/- 38 W/m2, respectively) and subjects sweated more in NC than in HC (P < 0.01). O2 consumption was lower initially in HC than in NC (P < 0.05), but O2 pulse was not different. It was concluded that precooling results in greater exercise endurance with enhanced heat storage rate and less stress on metabolic and cardiovascular systems.

Adult↗
PubMed1995

Exercise and mineral status of athletes: calcium, magnesium, phosphorus, and iron.

Calcium, magnesium, phosphorus, and iron are important to a wide variety of body functions, such as mineralization of bones, serving as cofactors to many enzyme systems, sustaining muscle and nerve excitation, and, in the case of iron, maintaining the oxygen carrying capacity of the blood. Many female athletes consume less calcium than the recommended dietary allowance (RDA). This is of concern because of the need to achieve peak bone mass during adolescence and the possible relationship of poor calcium intake to stress fractures. Athletes appear to have adequate magnesium and phosphorus status. However, those athletes who are on calorie-restricted diets may not be ingesting sufficient quantities of magnesium and possibly phosphorus. Limited data have suggested that magnesium status is indirectly related to strength improvement as well as the incidence of muscle cramps. Acute ingestion of phosphorus (phosphate loading) has been shown to improve aerobic capacity. Iron depletion is common in female athletes but similar to the general population. Iron supplements are of health benefit, but of questionable performance benefit, to those who are iron depleted and nonanemic. To maintain optimal status of these minerals, it is recommended that nutrient rich foods be ingested including dairy products and foods high in heme iron.

Adolescent↗
PubMed1994

Trace mineral requirements for 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.

Exercise↗
PubMed1993

Zinc loss in sweat of athletes exercising in hot and neutral temperatures.

Zinc (Zn) loss from sweat of 9 male and 9 female athletes exercising under hot (35 degrees C, HE) and neutral (25 degrees C, NE) 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 spectrophotometry. 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.

Adult↗
PubMed1993

Walking and running energy expenditure estimated by Caltrac and indirect calorimetry.

The purpose of this study was to examine the accuracy of the Caltrac personal activity computer during walking and running. Ten women and 10 men walked at speeds of 2-5 mph and ran at speeds of 4-8 mph on a horizontal treadmill. Two Caltrac monitors were attached over opposite hips: one programed to give caloric expenditure and the other to give Caltrac counts. Oxygen uptake was measured simultaneously. Significant correlations were found during walking between Caltrac estimated and actual energy expenditure (r = 0.91) and between activity counts and net exercise VO2.kg-1 (r = 0.87). However, the Caltrac significantly overestimated energy cost during horizontal walking at speeds above 2 mph. Although there was a significant correlation between Caltrac estimated and actual energy expenditure during running (r = 0.71), the correlation between Caltrac counts and net exercise VO2.kg-1 was not significant (r = 0.29). There was no significant increase in Caltrac kcal or counts with increased running speed between 5 and 8 mph. It is concluded that the Caltrac is a valid indicator of physical activity during walking but does not adequately discriminate between running speeds of 5-8 mph.

Calorimetry, Indirect↗
PubMed1993

Effects of iron repletion on VO2max, endurance, and blood lactate in women.

To determine the effects of an 8-wk dietary iron supplementation (100 mg.d-1) on low plasma ferritin concentration (< 20 ng.ml-1) and endurance, 20 active women (19-35 yr) were studied while performing a VO2max test and an endurance test (80% VO2max) on a cycle ergometer. Subjects were randomly placed in an iron supplement (IG) or a placebo group (PG) using a double-blind method. After treatment in the IG, ferritin levels were higher (22.5 +/- 3.4 vs 14.3 +/- 2.2 ng.ml-1; P < 0.05), Hb increased (12.8 +/- 0.4 to 14.1 +/- 0.2 g.dl-1; P < 0.05), and TIBC decreased (366.2 +/- 24.8 to 293.8 +/- 14.0 micrograms.dl-1; P < 0.05). Also after treatment the IG's VO2max was significantly greater (P < 0.05) than the PG value and their postendurance blood lactate decreased (5.03 +/- 0.44 to 3.85 +/- 0.6 mM.l-1; P < 0.05). Endurance time to exhaustion increased 38% (37.28 +/- 5.03 to 51.4 +/- 7.45 min) following iron treatment; however, this change was not statistically significant. The results suggest that this level of iron supplementation can reverse mild anemia, increase VO2max, and reduce blood lactate concentration after submaximal exercise.

Adolescent↗
PubMed1992

Effects of low ferritin concentration on endurance performance.

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 (< 12 ng/ml) plasma ferritin concentrations were studied while performing a VO2max and an endurance test (80% VO2max) on a cycle ergometer. The low ferritin group had significantly lower serum iron concentration and transferrin saturation and higher TIBC than the normal ferritin group. Mean VO2max 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) ferritin groups; however, the normal ferritin group exercised 14% longer. Blood lactate concentrations following the VO2max and endurance test did not differ significantly between groups. Food diaries revealed lower daily absorbable iron intake by the low ferritin 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.

Adult↗
PubMed1992

Effects of caffeine ingestion on metabolic responses to prolonged walking in sedentary males.

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% VO2max) and moderate (50% VO2max) aerobic intensities in eight sedentary (VO2max) 39.6 +/- 3.1 ml.kg-1 x 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 (p > 0.05). 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 caffeine-induced shift in energy substrate usage. Caffeine is not an effective means for enhancing the energy cost of prolonged walking.

Adult↗
PubMed1992

Substrate utilization during treadmill running in prepubertal girls and women.

Ten prepubertal girls (9.1 yr) and 10 women (24.4 yr) were studied during 30-min runs at the same relative (70% VO2max) (RI) and absolute (7.2 km.h-1) (AI) intensities. Oxygen consumption and respiratory exchange ratio (RER) were monitored continuously during the exercise test. Venous blood samples were obtained before and immediately after exercise and were analyzed for glucose, lactate, FFA, and glycerol. During exercise at the same RI, RER was significantly (P less than 0.05) lower in the girls compared with the women. In addition, RER decreased significantly during exercise in the girls while the change did not reach significance in the women. Lactate concentration increased significantly during the exercise tests, this increase being greater in the women than in the girls during exercise at the same RI, but greater in the girls than in the women during exercise at the same AI. FFA and glycerol concentrations were significantly higher after the exercise tests in both groups. Glucose concentration did not change significantly during the tests in either group. Prepubertal girls rely more on fat utilization and less on carbohydrate metabolism than women during exercise of moderately heavy intensity.

Adult↗
PubMed1991

Vitamin and mineral supplementation to athletes.

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, B6, B12, and E. Biochemical evidence of vitamin deficiencies in some athletes have been reported for thiamine, riboflavin, and B6. 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.

Exercise↗