Biomedical subjects
Douglas J Casa
Publications and source records attributed to Douglas J Casa.
No effect of 5% hypohydration on running economy of competitive runners at 23 degrees C.
PURPOSE: Although running economy (RE) is recognized as an integral component of successful endurance performance and is affected by numerous factors, little is known about the influence of body water loss on RE. This investigation examined the effects of hypohydration (HY) on RE and associated physiological responses. METHODS: Ten highly trained collegiate distance runners (mean +/- SD; age, 20 +/- 3 yr; height, 178.5 +/- 6.3 cm; body mass, 66.7 +/- 5.4 kg; VO2max, 66.5 +/- 4.1 mL x kg(-1) x min(-1)) participated in four experiments on separate days, twice in a euhydrated (EU) and twice in a HY state (-5.5 and -5.7% body mass loss achieved during 24 h). At each hydration level, subjects performed one 10-min treadmill run per day (23 degrees C environment), at either 70% VO2max (EU 70% or HY 70%) or 85% VO2max (EU 85% or HY 85%) in a randomized, repeated-measures design. Cardiopulmonary, metabolic, thermal, hormonal, and perceptual variables were measured. RESULTS: No between-treatment differences existed for RE (EU 70%, 46.3 +/- 3.2; HY 70%, 47.2 +/- 3.8; EU 85%, 58.6 +/- 2.8; HY 85%, 58.9 +/- 4.1 mL x kg(-1) x min(-1)), postexercise plasma lactate concentration (EU 70%, 1.9 +/- 0.6; HY 70%, 1.8 +/- 0.6; EU 85%, 6.5 +/- 3.5; HY 85%, 6.4 +/- 3.5 mmol x L(-1)), or rating of perceived exertion. HY resulted in a greater (P < 0.05 to 0.001) heart rate (HR), rectal temperature, and plasma norepinephrine concentration (NE), concurrent with reduced cardiac output, stroke volume, and respiratory exchange ratio. CONCLUSION: HY did not alter the RE or lactate accumulation of endurance athletes during 10 min of exercise at 70 and 85% VO2max. These findings indicate that HY had no effect on RE, but that it increased physiological strain in a 23 degrees C environment.
Survival strategy: acute treatment of exertional heat stroke.
Explore the source record for details and available documents.
Heat acclimatization and hydration status of American football players during initial summer workouts.
This investigation evaluated the new National Collegiate Athletic Association model of heat acclimatization for football players using physiological, psychological, fluid balance, anthropometric, and nutritional variables. Eleven football players (20 +/- 1 year, 1.88 +/- 0.05 m, and 115.36 +/- 18.85 kg) from a Division I football team were observed for the first 8 days of preseason practices. Measurements such as heart rate and gastrointestinal temperature (T(GI)) via telemetric sensor were taken before, 3 times during, and after practice daily. An average 1.39-kg (1.2%) decrease of body mass occurred from prepractice to postpractice (p < 0.01). Consistent with mild body mass losses, urinary indices of hydration status (i.e., color, specific gravity, and osmolality) indicated mild fluid deficits. A significant increase (p < 0.05) from pre- to postpractice was observed in urine color and urine specific gravity, but chronic hypohydration over the 8 days was not noted. The Environmental Symptoms Questionnaire (ESQ) postpractice score was significantly higher (p < 0.05) than the prepractice score was, but averages did not differ across practice days. There was no difference in postpractice T(GI) measurements across days (p < 0.05). Heart rate, T(GI), and ESQ measurements indicated that football players experienced gradual heat acclimatization and enhanced heat tolerance, despite progressive increases of exercise variables, clothing, and environmental stressors.
Body cooling between two bouts of exercise in the heat enhances subsequent performance.
The purpose was to assess whether body cooling between 2 bouts of exercise in the heat enhances performance during the second exercise session. Using a random, crossover design, 15 subjects (3 women, 12 men; 28 +/- 2 years, 180 +/- 2 cm, 69 +/- 2.3 kg) participated in all 3 trials. Subjects ran 90 minutes on hilly trails in a hot environment (approximately 27 degrees C) before 12 minutes of either cold water immersion (CWI; 13.98 degrees C), ice water immersion (IWI; 5.23 degrees C), or a mock treatment (MT) of sitting in a tub with no water (29.50 degrees C). After immersion, subjects ran a 2-mile race. CWI had faster (p < 0.05) performance time (725 seconds) than MT (769 seconds). CWI and IWI had significantly (p < 0.05) lower rectal temperatures postimmersion than MT as well as postrace (p < 0.05). Heart rate also remained significantly lower (p < 0.05) during the CWI and IWI trials for the first half of the race. In conclusion, CWI enhances performance (6% improvement in race time) in the second bout of exercise, supporting its potential role as an ergogenic aid in athletic performance.
Thermoregulatory responses to exercise in the heat: chronic caffeine intake has no effect.
INTRODUCTION: Authorities advise individuals to refrain from caffeine intake before or during exercise, especially when performed in the heat, due to potential fluid-electrolyte imbalances that exaggerate physiological strain. Yet, military personnel are often deployed to hot environments and must perform under sleep-deprived conditions where caffeine would be an ideal intervention strategy to enhance physical and cognitive performance. PURPOSE: To assess the effects of controlled chronic and acute caffeine ingestion on fluid-electrolyte, physiological and thermoregulatory responses during an exercise heat tolerance test (EHT). METHODS: Subjects were 59 active, college-aged males (mean +/- SE 21.6 +/- 0.4 yr, 177.9 +/- 0.8 cm, 75.4 +/- 1.0 kg, 11.1 +/- 0.7% body fat) who were randomized and stratified by age, bodyweight, and body composition into three groups. All subjects equilibrated caffeine intake at 3 mg x kg(-1) x d(-1) for days 1-6. On days 7-12, they consumed a treatment dose of either 0 (G0), 3 (G3), or 6 (G6) mg x kg(-1) x d(-1). Fluid-electrolyte and physiological measures were made on day 12, 1 h after caffeine intake, during the EHT (90 min walking, 1.56 m x s(-1), 5% grade; dry bulb temperature, 37.7 +/- 0.1 degree C; relative humidity, 56.3 -1.5%). RESULTS: There were no between-group differences (p > 0.05) in plasma, urinary, thermoregulatory, cardiovascular, and perceptual variables across time (pre- vs. post-EHT), although some of these variables increased significantly over time (p < 0.05). EHT time was significantly greater in G3 (86 +/- 2.0 min) vs. GO (75 +/- 3.3 min, p < 0.05). DISCUSSION: Acute caffeine ingestion, in chronically consuming subjects (3 and 6 mg x kg(-1) x d(-1)) did not alter fluid-electrolyte, exercise endurance or thermoregulatory responses during EHT when compared with G0.
Rehydration with glycerol: endocrine, cardiovascular, and thermoregulatory responses during exercise in the heat.
The impact of rehydration with glycerol on cardiovascular and thermoregulatory responses during exercise in the heat was studied in eight highly trained male cyclists. Each subject completed three dehydration-rehydration experimental trials that differed only in the rehydration treatment, each separated by 7 days. Before each experimental day, subjects dehydrated to -4% of their body weight by exercise and water restriction. The experimental treatments were as follows: no fluid (NF), glycerol bolus (1 g/kg body wt) followed by water (G), and water alone (W). Rehydration (3% body weight) was given over an 80-min period. After rehydration, subjects cycled (74% peak O2 uptake) to exhaustion in a hot and wet (37 degrees C and 48% relative humidity) environment. For G, plasma volume was expanded (P < 0.05) during rehydration and remained higher than W (P < 0.05) during exercise. Exercise time to exhaustion during G (33 +/- 4 min) was longer (P < 0.05) compared with both W (27 +/- 3 min) and NF (19 +/- 3 min). Cutaneous vascular conductance was significantly elevated (P < 0.05) during G, but G provided no other thermoregulatory or cardiovascular benefits compared with W and NF. Fluid-regulating hormones (vasopressin, aldosterone, atriopeptin, and plasma renin activity) decreased during rehydration and increased during exercise (except atriopeptin), but there were no differences between G and W. These data indicated that glycerol had little or no major effect on fluid-regulating factors during rehydration or exercise, and the improved exercise capacity in G was likely due to a greater plasma volume during exercise.
Effect of chronic caffeine intake on choice reaction time, mood, and visual vigilance.
The stimulatory effects of acute caffeine intake on choice reaction time, mood state, and visual vigilance are well established. Little research exists, however, on the effects of chronic caffeine ingestion on psychomotor tasks. Therefore, the purpose of this study was to evaluate the effects of 5 days of controlled caffeine intake on cognitive and psychomotor performance. Three groups of 20 healthy males (age=22+/-3 years, mass=75.4+/-7.9 kg, body fat percentage=11.2+/-5.1%) twice completed a battery of cognitive and psychomotor tasks: after 6 days of 3 mg.kg(-1) day(-1) caffeine equilibration (Day 6), and after 5 days of experimental (0 [G0], 3 [G3], or 6 [G6] mg.kg(-1) day(-1)) caffeine intake (Day 11). Groups were randomized and stratified for age, mass, and body composition; all procedures were double-blind. Cognitive analyses involved a visual four-choice reaction time test, a mood state questionnaire, and a visual vigilance task. Experimental chronic caffeine intake did not significantly alter the number of correct responses or the mean latency of response for either the four-choice reaction time or the visual vigilance tasks. The Vigor-Activity subset of the mood state questionnaire was significantly greater in G3 than G0 or G6 on Day 11. All other mood constructs were unaffected by caffeine intake. In conclusion, few cognitive and psychomotor differences existed after 5 days of controlled caffeine ingestion between subjects consuming 0, 3, or 6 mg.kg(-1) day(-1) of caffeine, suggesting that chronic caffeine intake (1) has few perceptible effects on cognitive and psychomotor well-being and (2) may lead to a tolerance to some aspects of caffeine's acute effects.
American College of Sports Medicine roundtable on hydration and physical activity: consensus statements.
Explore the source record for details and available documents.
Exertional heat stroke in competitive athletes.
Exertional heat stroke (EHS) is a serious medical condition that can have a tragic outcome if proper assessment and treatment are not initiated rapidly. This article focuses on critical misconceptions that pertain to the prevention, recognition, and treatment of EHS, including 1) the randomness of EHS cases, 2) the role of nutritional supplements in EHS, 3) temperature assessment, 4) onset of EHS and the possible lucid interval, 5) rapid cooling, and 6) return to play. Exploration of these topics will enhance the medical care regarding EHS.
Fluid, electrolyte, and renal indices of hydration during 11 days of controlled caffeine consumption.
This investigation determined if 3 levels of controlled caffeine consumption affected fluid-electrolyte balance and renal function differently. Healthy males (mean +/- standard deviation; age, 21.6 +/- 3.3 y) consumed 3 mg caffeine . kg(-1) . d(-1). on days 1 to 6 (equilibration phase). On days 7 to 11 (treatment phase), subjects consumed either 0 mg (C0; placebo; n= 20), 3 mg (C3; n = 20), or 6 mg (C6; n = 19) caffeine . kg(-1) . d(-1) in capsules, with no other dietary caffeine intake. The following variables were unaffected (P > 0.05) by different caffeine doses on days 1, 3, 6, 9, and 11 and were within normal clinical ranges: body mass, urine osmolality, urine specific gravity, urine color, 24-h urine volume, 24-h Na+ and K+ excretion, 24-h creatinine, blood urea nitrogen, serum Na+ and K+, serum osmolality, hematocrit, and total plasma protein. Therefore, C0, C3, and C6 exhibited no evidence of hypohydration. These findings question the widely accepted notion that caffeine consumption acts chronically as a diuretic.
Influence of diuretic-induced dehydration on competitive sprint and power performance.
UNLABELLED: Diuretic-induced dehydration impairs prolonged running performance (> 1500 m). Sprinting performance may suffer by similar mechanisms (i.e., altered cardiovascular strain, heat storage, and metabolism) or may improve because of reduced mass to accelerate and carry. PURPOSE: To examine sprint and power performance after diuretic-induced dehydration. METHODS: After six sprint practice sessions, nine male former sprinters (mean +/- SD; age, 21 +/- 2 yr; body mass (BM), 80.0 +/- 5.2 kg; height, 1.78 +/- 0.08 m; body fat, 14 +/- 4%) participated in a 50-m race, a 200-m race, a 400-m race, and a vertical jump on an indoor synthetic track, once when dehydrated (40-mg furosemide; DD) and once with no diuretic (CON) using a counter-balanced crossover design. Plasma volume change (%deltaPV), heart rate (HR), blood pressure, rectal temperature, serum electrolytes, plasma lactate, plasma glucose, rating of perceived exertion, thirst, and thermal sensations were measured before and after each race. RESULTS: Sprint times (DD vs CON) for the 50 m (6.72 +/- 0.28 vs 6.73 +/- 0.29 s), 200 m (25.95 +/- 1.20 vs 26.21 +/- 1.42 s), and 400 m (59.01 +/- 4.26 vs 58.68 +/- 3.68 s) were similar for both conditions, as was vertical jump height (0.67 +/- 0.10 vs 0.66 +/- 0.11 m). This occurred despite losing 2.2 +/- 0.4% BM and 7.3 +/- 6.7%deltaPV (50/200 m) or 2.5 +/- 0.4% BM and 7.1 +/- 2.7% deltaPV (VJ/400 m) in response to DD. CONCLUSIONS: Diuretic-induced dehydration was not detrimental to sprint and power performance. Metabolic, thermoregulatory, and cardiovascular variables were not significantly altered by DD. Furthermore, the theoretical benefit of dehydration on performance (i.e., BM reduction) was not supported in this subject cohort.
Youth football: heat stress and injury risk.
Explore the source record for details and available documents.
Rehydration with a caffeinated beverage during the nonexercise periods of 3 consecutive days of 2-a-day practices.
The purpose of this study was to assess the influence of rehydration with a caffeinated beverage during nonexercise periods on hydration status throughout consecutive practices in the heat. Ten (7 women, 3 men) partially heat- acclimated athletes (age 24 +/-1y, body fat 19.2 +/- 2 %, weight 68.4 +/- 4.0 kg, height 170 +/- 3 cm) completed 3 successive days of 2-a-day practices (2 h/practice, 4 h/d) in mild heat (WBGT = 23 C). The 2 trials (double-blind, random, cross-over design) included; 1) caffeine (CAF) rehydrated with Coca-Cola and 2) caffeine-free (CF) rehydrated with Caffeine-Free Coca-Cola. Urine and psychological measures were determined before and after each 2-h practice. A significant difference was found for urine color for the post-AM time point, F = 5.526, P = 0.031. No differences were found among other variables (P > 0.05). In summary, there is little evidence to suggest that the use of beverages containing caffeine during nonexercise might hinder hydration status.
Ice-Water Immersion and Cold-Water Immersion Provide Similar Cooling Rates in Runners With Exercise-Induced Hyperthermia.
OBJECTIVE: To assess whether ice-water immersion or cold-water immersion is the more effective treatment for rapidly cooling hyperthermic runners. DESIGN AND SETTING: 17 heat-acclimated highly trained distance runners (age = 28 +/- 2 years, height = 180 +/- 2 cm, weight = 68.5 +/- 2.1 kg, body fat = 11.2 +/- 1.3%, training volume = 89 +/- 10 km/wk) completed a hilly trail run (approximately 19 km and 86 minutes) in the heat (wet-bulb globe temperature = 27 +/- 1 degrees C) at an individually selected "comfortable" pace on 3 occasions 1 week apart. The random, crossover design included (1) distance run, then 12 minutes of ice-water immersion (5.15 +/- 0.20 degrees C), (2) distance run, then 12 minutes of cold-water immersion (14.03 +/- 0.28 degrees C), or (3) distance run, then 12 minutes of mock immersion (no water, air temperature = 28.88 +/- 0.76 degrees C). MEASUREMENTS: Each subject was immersed from the shoulders to the hip joints for 12 minutes in a tub. Three minutes elapsed between the distance run and the start of immersion. Rectal temperature was recorded at the start of immersion, at each minute of immersion, and 3, 6, 10, and 15 minutes postimmersion. No rehydration occurred during any trial. RESULTS: Length of distance run, time to complete distance run, rectal temperature, and percentage of dehydration after distance run were similar (P >.05) among all trials, as was the wet-bulb globe temperature. No differences (P >.05) for cooling rates were found when comparing ice-water immersion, cold-water immersion, and mock immersion at the start of immersion to 4 minutes, 4 to 8 minutes, and the start of immersion to 8 minutes. Ice-water immersion and cold-water immersion cooling rates were similar (P >.05) to each other and greater (P <.05) than mock immersion at 8 to 12 minutes, the start of immersion to 10 minutes, and the start of immersion to every other time point thereafter. Rectal temperatures were similar (P >.05) between ice-water immersion and cold-water immersion at the completion of immersion and 15 minutes postimmersion, but ice-water immersion rectal temperatures were less (P <.05) than cold-water immersion at 6 and 10 minutes postimmersion. CONCLUSIONS: Cooling rates were nearly identical between ice-water immersion and cold-water immersion, while both were 38% more effective in cooling after 12 minutes of immersion than the mock-immersion trial. Given the similarities in cooling rates and rectal temperatures between ice-water immersion and cold-water immersion, either mode of cooling is recommended for treating the hyperthermic individual.
National Athletic Trainers' Association Position Statement: Exertional Heat Illnesses.
OBJECTIVE: To present recommendations for the prevention, recognition, and treatment of exertional heat illnesses and to describe the relevant physiology of thermoregulation. BACKGROUND: Certified athletic trainers evaluate and treat heat-related injuries during athletic activity in "safe" and high-risk environments. While the recognition of heat illness has improved, the subtle signs and symptoms associated with heat illness are often overlooked, resulting in more serious problems for affected athletes. The recommendations presented here provide athletic trainers and allied health providers with an integrated scientific and practical approach to the prevention, recognition, and treatment of heat illnesses. These recommendations can be modified based on the environmental conditions of the site, the specific sport, and individual considerations to maximize safety and performance. RECOMMENDATIONS: Certified athletic trainers and other allied health providers should use these recommendations to establish on-site emergency plans for their venues and athletes. The primary goal of athlete safety is addressed through the prevention and recognition of heat-related illnesses and a well-developed plan to evaluate and treat affected athletes. Even with a heat-illness prevention plan that includes medical screening, acclimatization, conditioning, environmental monitoring, and suitable practice adjustments, heat illness can and does occur. Athletic trainers and other allied health providers must be prepared to respond in an expedient manner to alleviate symptoms and minimize morbidity and mortality.
Question everything: the value of integrating research into an athletic training education.
Explore the source record for details and available documents.
Creatine use and exercise heat tolerance in dehydrated men.
CONTEXT: Creatine monohydrate (CrM) use is highly prevalent in team sports (eg, football, lacrosse, ice hockey) and by athletes at the high school, college, professional, and recreational levels. Concerns have been raised about whether creatine use is associated with increased cramping, muscle injury, heat intolerance, and risk of dehydration. OBJECTIVE: To assess whether 1 week of CrM supplementation would compromise hydration status, alter thermoregulation, or increase the incidence of symptoms of heat illness in dehydrated men performing prolonged exercise in the heat. DESIGN: Double-blind, randomized, crossover design. SETTING: Human Performance Laboratory. PATIENTS OR OTHER PARTICIPANTS: Twelve active males, age = 22 +/- 1 year, height = 180 +/- 3 cm, mass = 78.8 +/- 1.2 kg, body fat = 9 +/- 1%, V(O2)peak = 50.9 +/- 1 ml.kg(-1).min(-1). INTERVENTION(S): Subjects consumed 21.6 g.d(-1) of CrM or placebo for 7 days, underwent 48 +/- 10 days of washout between treatments, and then crossed over to the alternate treatment in the creatine group. On day 7 of each treatment, subjects lost 2% body mass by exercising in 33.5 degrees C and then completed an 80-minute exercise heat-tolerance test (33.5 degrees C +/- 0.5 degrees C, relative humidity = 41 +/- 12%). The test consisted of four 20-minute sequences of 4 minutes of rest, alternating a 3-minute walk and 1-minute high-intensity run 3 times, and walking for 4 minutes. MAIN OUTCOME MEASURES: Thermoregulatory, cardiorespiratory, metabolic, urinary, and perceptual responses. RESULTS: On day 7, body mass had increased 0.88 kg. No interaction or treatment differences for placebo versus CrM during the exercise heat-tolerance test were noted in thermoregulatory (rectal temperature, 39.3 +/- 0.4 degrees C versus 39.4 +/- 0.4 degrees C) cardiorespiratory (Vo(2), 21.4 +/- 2.7 versus 20.0 +/- 1.8 ml.kg(-1).min(-1); heart rate, 192 +/- 10 versus 192 +/- 11 beats.min(-1); mean arterial pressure, 90 +/- 9 versus 88 +/- 5 mm Hg), metabolic (lactate, 6.7 +/- 2.7 versus 7.0 +/- 3.0 mmol.L(-1)), perceptual thirst (thirst, 7 +/- 1 versus 7 +/- 1; thermal sensation, 8 +/- 2 versus 8 +/- 1; rating of perceived exertion, 17 +/- 3 versus 17 +/- 2), plasma glucose (0-20 minutes of exercise heat-tolerance, 6.5 +/- 1.2 versus 6.8 +/- 0.8 mmol.L(-1)), plasma (297 +/- 5 versus 300 +/- 4 mOsm.kg(-1)) and urine (792 +/- 117 versus 651 +/- 134 mOsm.kg(-1)), urine specific gravity (1.025 +/- 0.003 versus 1.030 +/- 0.005) and urine color (7 +/- 1 versus 6 +/- 1) measures were increased during CrM. Environmental Symptoms Questionnaire scores were similar between treatments. The levels of dehydration incurred during dehydration and the exercise heat-tolerance test were similar and led to similar cumulative body mass losses (-4.09 +/- 0.53 versus -4.38 +/- 0.58% body mass). CONCLUSIONS: Short-term CrM supplementation did not increase the incidence of symptoms or compromise hydration status or thermoregulation in dehydrated, trained men exercising in the heat.