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Biomedical subjects

Greig Watson

Publications and source records attributed to Greig Watson.

9 recordsLinked to original sources
PubMed2006

Pituitary-adrenal responses to arm versus leg exercise in untrained man.

The purpose of this study was to examine pituitary-adrenal (PA) hormone responses [beta-endorphin (beta-END), adrenocorticotropic hormone (ACTH) and cortisol] to arm exercise (AE) and leg exercise (LE) at 60 and 80% of the muscle-group specific VO2 peak. Eight healthy untrained men (AE VO2 peak=32.4+/-3.0 ml kg(-1) min(-1), LE VO2 peak=46.9+/-5.3 ml kg(-1) min(-1)) performed two sub-maximal AE and LE tests in random order. Plasma beta-END, ACTH and cortisol were not different (P>0.05) between AE and LE at either exercise intensity; the 60% testing elicited no changes from pre-exercise (PRE) values. For 80% testing, plasma beta-END, ACTH and cortisol were consistently, but not significantly, greater during LE than AE. In general, plasma beta-END and ACTH were higher (P<0.05) during 80% exercise, than PRE, for both AE and LE. Plasma cortisol was elevated (P<0.05) above PRE during 80% LE, and following 80% for both AE and LE. Plasma ACTH was higher (P<0.05) during 80% LE and AE versus 60% LE and AE, respectively. Plasma beta-END and cortisol were significantly higher during and immediately after 80% LE than 60% LE. Thus, plasma beta-END, ACTH and cortisol responses were similar for AE and LE at the two relative exercise intensities, with the intensity threshold occurring somewhere between 60 and 80% of VO2 peak. It appears that the smaller muscle mass associated with AE was sufficient to stimulate these PA axis hormones in a manner similar to LE, despite the higher metabolic stress (i.e., plasma La-) associated with LE.

Adrenocorticotropic Hormone↗
PubMed2006

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.

Adaptation, Physiological↗
PubMed2006

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.

Adult↗
PubMed2005

Cortitrol supplementation reduces serum cortisol responses to physical stress.

The supplement Cortitrol was formulated to mitigate the cortisol response to physiological and psychological stress. Therefore, the purpose of this study was to examine the effects of Cortitrol on serum cortisol concentrations before, during, and after a high-intensity resistance exercise protocol (EX) and a resting control day (REST). We used a matched, balanced, randomized, double-blind, placebo-controlled, cross-over design. Blood samples were obtained at matching time points during EX and REST. Cortitrol significantly ( P < .05) reduced cortisol area under the curve concentrations during REST. During EX, Cortitrol reduced cortisol concentrations at 20, 10, and 0 minutes pre-exercise, at mid-exercise, immediately post-exercise, and at 5 minutes post-exercise. In addition, serum cortisol and plasma adrenocorticotropin hormone area under the curve concentrations during EX were significantly lower after Cortitrol than placebo. Furthermore, Cortitrol significantly reduced free radical production. This was indicated by significantly lower plasma malondialdehyde concentrations at the 65-minute post-exercise time point during REST, and at pre-exercise, immediate post-exercise, and 65 minutes post-exercise during EX. Serum total testosterone, free testosterone, dehydroepiandrosterone, and growth hormone showed exercise-induced increases but no treatment effects. These data demonstrate that Cortitrol was effective in modulating the physiological stress responses of exercise from the anticipatory rises before physical stress and into early recovery by reducing cortisol and associated free radical production.

Adrenocorticotropic Hormone↗
PubMed2005

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.

Adolescent↗
PubMed2005

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.

Adult↗
PubMed2003

The effects of exertional heatstroke and exercise-heat acclimation on plasma beta-endorphin concentrations.

INTRODUCTION: It has been suggested that a proopiomelanocortin peptide beta-endorphin may play an important role in temperature regulation and therefore have specific heat stroke response patterns. METHODS: The purpose of this study was to examine the response patterns of plasma beta-endorphin at baseline, during a 7-d exercise-heat acclimation period (HA; 90 min x d(-1), 40 degrees C), and during a 6-h exercise-heat tolerance test (HTT; 6 h, 40 degrees C) performed before and after HA. Subjects were nine previously diagnosed heatstroke patients (P) and eight matched controls (C). No differences between the two groups were observed at rest, prior to HTT. RESULTS: Plasma beta-endorphin concentration in P significantly increased above resting values at 2, 4, and 6 h of HTT and were significantly greater than C responses. During HA tests, a significantly higher beta-endorphin concentration was observed in P before exercise on day 1 and day 7, but not on day 4. A significant increase occurred after exercise in both groups, on all days of HA; no differences were observed between the groups on days 4 and 7. DISCUSSION: These results demonstrate that the opioid peptide responses in individuals with recent exertional heatstroke were greater than control subjects during the initial 6-h HTT. Decreased physical training among P may have contributed to these results. However, 7 d of HA abolished these between-group differences by reducing the magnitude of beta-endorphin responses in P, indicative of an adaptation of pituitary function.

Acclimatization↗
PubMedDate not supplied

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.

Journal Article↗