Biomedical subjects

S D Galloway

Publications and source records attributed to S D Galloway.

11 recordsLinked to original sources

PubMed2001

Exogenous carbohydrate oxidation from drinks ingested during prolonged exercise in a cold environment in humans.

Six healthy male volunteers performed four rides to exhaustion on a cycle ergometer at approximately 80% of maximal oxygen consumption. Subjects ingested a bolus volume of fluid (7.14 ml/kg) immediately before exercise and additional fluid volumes (1.43 ml/kg) every 10 min during exercise. The fluids ingested were either a flavored water control or glucose-electrolyte beverages with glucose concentrations of 2, 6, or 12%. The beverages were labeled with [U-(13)C]glucose (99.2%: 0.05 g/l). Exercise capacity was not different (P = 0.13) between trials; median (range) exercise time was 83.52 (79.85--89.68), 103.19 (78.82--108.22), 100.37 (80.60--124.07), and 94.76 (76.78--114.25) min in the 0, 2, 6, and 12% trials, respectively. The oxidation of exogenous glucose in each 15-min period was significantly lower in the 2% trial (P = 0.02) than in the 6 and 12% trials where oxidation rates were between 0.5 and 0.7 g/min. No difference in endogenous glucose oxidation was observed between trials (P = 0.71). These findings indicate that the oxidation of exogenous glucose during exercise of this intensity and duration in a cold environment is similar to that observed in warmer conditions. Thus a low oxidation of exogenous substrate is unlikely to be a factor limiting the effectiveness of carbohydrate-electrolyte drink ingestion on exercise capacity in a cold environment.

Acclimatization↗

PubMed2000

Effects of moderate dietary manipulation on intermittent exercise performance and metabolism in women.

The aim of the current study was to examine the effect of a moderate alteration in pre-exercise diet composition on the performance of, and metabolic response to, intermittent treadmill exercise in a group of normally menstruating females. Eight recreationally active women performed two intermittent, incremental exercise trials, one preceded by 2 days of a high [61 (1)%] carbohydrate (CHO) diet and the other by 2 days of a low [31 (1)%] CHO diet. Oxygen uptake (VO2) was measured during, and blood samples were obtained immediately after, each bout for the determination of blood lactate, glucose, glycerol, plasma free fatty acids and plasma ammonia. Performance, as assessed by time to exhaustion in the final bout, was found to be similar whether preceded by a high- or low-CHO diet [median (range): 28.0 (18-54) s, 29 (18-54) s, respectively]. No significant between trial differences were found in VO2, heart rate, or any of the blood metabolites. The results of the current, study indicate that moderate alterations of pre-exercise diet do not affect intermittent, high-intensity exercise performance in women, despite some evidence of an alteration in the pattern of the metabolic response to exercise.

Adult↗

PubMed2000

The effects of substrate and fluid provision on thermoregulatory and metabolic responses to prolonged exercise in a hot environment.

A high ambient temperature reduces the capacity to perform prolonged exercise. Total carbohydrate oxidation is less, and thus glycogen depletion is not limiting. Fluid ingestion in the heat should, therefore, focus on maintenance of hydration status rather than on substrate provision. Six healthy males cycled to exhaustion at 60% of maximum oxygen consumption (VO2max) with no drink, ingestion of a 15% carbohydrate-electrolyte drink (1.45+/-0.29 litres) or ingestion of a 2% carbohydrate-electrolyte drink (3.12+/-0.47 litres). The ambient temperature was 30.2+/-0.6 degrees C (mean +/- s), with a relative humidity of 71+/-1% and an air speed of approximately 0.7 m x s(-1) on all trials. Weighted mean skin temperature, rectal temperature and heart rate were recorded and venous samples drawn for determination of plasma volume changes, blood metabolites, serum electrolytes and osmolality. Expired gas was collected to estimate rates of fuel oxidation. Exercise capacity was significantly (P < 0.05) different in all trials. The median (range) time to exhaustion was 70.9 min (39.4-97.4 min) in the no-drink trial, 84.0 min (62.7-145 min) in the 15% carbohydrate trial and 118 min (82.6-168 min) in the 2% carbohydrate trial. The 15% carbohydrate drink resulted in significantly (P < 0.05) elevated blood glucose and total carbohydrate oxidation compared with the no-drink trial. The 2% carbohydrate drink restored plasma volume to pre-exercise values by the end of exercise. No differences were observed in other thermoregulatory or cardiorespiratory responses between trials. These results suggest that fluid replacement with a large volume of a dilute carbohydrate drink is beneficial during exercise in the heat, but the precise mechanisms for the improved exercise capacity are unclear.

Adult↗

PubMed2000

Variations in regional sweat composition in normal human males.

This project aimed to quantify the regional distribution of sweat composition over the skin surface and to determine whether sweat constituent concentrations collected from regional sites can estimate whole-body concentrations. Ten males cycled for 90 min in a 20 degrees C (50% relative humidity) environment at 45% peak aerobic power. Sweat was collected from eleven skin regions and the whole body, using a wash-down technique. Strong relationships were evident between the regional and whole-body sweat [Na+] and [Cl-], such that the thigh and calf exhibited greater correlation coefficients than area-weighted means derived from four and eight skin regions. Therefore, in this particular protocol the whole-body sweat [Na+] and [Cl-] could be predicted from regional sweat collections. Relationships between sweat constituents were evident for sweat [Na+] and pH, and sweat [K+] and [lactate] when data were pooled between skin regions and subjects. To our knowledge this is the first investigation to report a positive relationship between sweat [K+] and [lactate]. The exact mechanism responsible for the positive relationship between sweat [K+] and [lactate] is uncertain although it is speculated to occur at the secretory coil.

Adult↗

PubMed2000

Effects of sympathetic inhibition on exertional dyspnoea, ventilatory and metabolic responses to exercise in normotensive humans.

Augmentation of circulating noradrenaline concentration stimulates ventilation during the initial stages of exercise and this is accompanied by an increased sensation of dyspnoea and exertion. This previous study [Clark, Galloway, MacFarlane, Henderson, Aitchison and McMurray (1997) Eur. Heart J. 18, 1829-1833] suggested a link between dyspnoea, which commonly limits exercise tolerance in heart failure patients, and high circulating noradrenaline concentration in these patients. The present study investigated this relationship further using sympathetic inhibition. Ten healthy normotensive males performed 10 min of submaximal cycling exercise at approx. 70% of maximal oxygen uptake per min (VO2max) on three occasions one week apart. The first of these sessions was a familiarization session and the other two were experimental study days. On each of the study days, subjects attended the laboratory in the morning after an overnight fast and, following a resting blood sample, were administered placebo or moxonidine (0.4 mg) in a double blind cross-over design. After a 90-min absorption period, subjects undertook the exercise task. Blood was drawn, expired gas was analysed breath by breath, blood pressure, heart rate and ratings of perceived dyspnoea and exertion were obtained. Moxonidine treatment significantly reduced plasma noradrenaline concentration (P < 0.01), mean arterial pressure (P < 0.01), and blood glycerol concentration (P < 0.05), but no differences were observed in heart rate, the ventilatory response to exercise or subjective ratings of dyspnoea and exertion. This study indicates that reducing sympathetic activity does not affect ventilation, perceived dyspnoea or perceived exertion in normotensive males. Therefore it can be concluded that reducing sympathetic activity may not be an appropriate strategy to help reduce perceived dyspnoea.

Adult↗

PubMed1999

Dehydration, rehydration, and exercise in the heat: rehydration strategies for athletic competition.

Exercise capacity and exercise performance are reduced when the ambient temperature is high. This has mainly been attributed to the large sweat losses which lead to hypohydration, a failure of thermoregulation, and eventually circulatory collapse. Exercising athletes rarely drink enough before or during exercise to replace the ongoing fluid losses, especially in hot conditions. In order to combat dehydration, hyperthermia, and impending circulatory collapse, athletes should drink fluids before, during, and after exercise. Preexercise strategies include attempts to maintain euhydration but also to hyperhydrate. Hyperhydration is relatively easy to achieve, but thermoregulatory benefits during prolonged exercise have not been observed in comparison to euhydration. In prolonged continuous exercise, fluid and carbohydrate (CHO) ingestion has clearly been shown to improve performance, but the evidence is not so clear for high-intensity intermittent exercise over a prolonged period. The general consensus is that fluid ingestion should match sweat losses during exercise and that the drink should contain CHO and electrolytes to assist water transport in the intestine and to improve palatability. Postexercise rehydration is essential when the strategies adopted before or during exercise have not been effective. The best postexercise rehydration strategy would be to ingest a large volume of a beverage that contains a CHO source and a high sodium content.

Beverages↗

PubMed1998

The effects of substrate and fluid provision on thermoregulatory, cardiorespiratory and metabolic responses to prolonged exercise in a cold environment in man.

During prolonged exercise in a cold environment, fatigue is generally associated with a depletion of endogenous glycogen stores. This has lead many authors to hypothesize that the carbohydrate (CHO) content of fluids ingested in cool environments should be high, yet this hypothesis has not been specifically examined. In the present study, six healthy males cycled to exhaustion at approximately 80% of their maximum oxygen consumption (V2O,max) with either no drink (ND), a 15% CHO-electrolyte drink (15% CHO) or a 2% CHO electrolyte drink (2% CHO). Dietary intake and exercise were replicated 2 days prior to each trial. Mean (S.D.) ambient temperature was 10.0 (0.3) degrees C with a relative humidity of 72 (2) % and an air velocity of approximately 0.7 m s(-1) on all trials. Weighted mean skin temperature was calculated, and rectal temperature and heart rate were recorded at rest, during exercise and at exhaustion. Venous samples were drawn before and during exercise and at exhaustion for determination of haemoglobin, haematocrit, blood metabolites and serum electrolytes and osmolality. Expired air was collected for calculation of VO2 and respiratory exchange ratio which were used to estimate rates of fuel oxidation. Ratings of perceived exertion (RPE) were also obtained. Exercise capacity was not different (P=0.49) between trials, with median (range) times to exhaustion of 90.6 (66.8-106.0), 97.7 (60.9-112.0) and 102.0 (77.1-170.7) min for the ND, 15% CHO and 2% CHO trials, respectively. The 15% CHO drink significantly (P < 0.05) elevated blood glucose concentration and total CHO oxidation compared with the ND trial. The 2% CHO drink significantly (P < 0.05) reduced the estimated change in plasma volume and resulted in a lower serum osmolality than the other two trials. No differences were observed in any thermoregulatory or cardiorespiratory responses between trials. These data suggest that maintenance of blood-borne substrate and/or plasma volume does not influence exercise capacity in the cold, as is commonly reported during this type and intensity of exercise in warmer environments.

Adult↗

PubMed1997

Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man.

Eight healthy males performed four rides to exhaustion at approximately 70% of their VO2max obtained in a neutral environment. Subjects cycled at ambient temperatures (Ta) of 3.6 +/- 0.3 (SD), 10.5 +/- 0.5, 20.6 +/- 0.2, and 30.5 +/- 0.2 degrees C with a relative humidity of 70 +/- 2% and an air velocity of approximately 0.7 m.s-1. Weighted mean skin temperature (Tsk), rectal temperature (Tre), and heart rate (HR) were recorded at rest, during exercise and at exhaustion. Venous samples were drawn before and during exercise and at exhaustion for determination of hemoglobin, hematocrit, blood metabolites, and serum electrolytes and osmolality. Expired air was collected for calculation of VO2 and R which were used to estimate rates of fuel oxidation. Ratings of perceived exertion (RPE) were also obtained. Time to exhaustion was significantly influenced by Ta (P = 0.001): exercise duration was shortest at 30.5 degrees C (51.6 +/- 3.7 min) and longest at 10.5 degrees C (93.5 +/- 6.2 min). Significant effects of Ta were also observed on VE, VO2, R, estimated fuel oxidation, HR, Tre, Tsk, sweat rate, and RPE. This study demonstrates that there is a clear effect of temperature on exercise capacity which appears to follow an inverted U relationship.

Adult↗

PubMed1996

The effects of acute phosphate supplementation in subjects of different aerobic fitness levels.

Six trained cyclists (high-fitness group) and six untrained individuals (low-fitness group), performed a 20-min cycle ergometer exercise test at 70% of maximum oxygen consumption (VO2max) followed by a 30-min rest period and then an incremental ride to exhaustion on two occasions, 1 week apart. Ninety minutes prior to exercise subjects consumed a drink containing either 22.2 g dibasic calcium phosphate (DCP; treatment) or calcium carbonate (placebo). Blood was drawn prior to drink ingestion, during submaximal exercise, during recovery and at exhaustion for determination of blood 2,3-DPG, blood ATP, plasma lactate, plasma phosphate, haemoglobin and haematocrit. Throughout exercise, cardiorespiratory variables [oxygen uptake (VO2), minute ventilation, (VE), respiratory exchange ratio, heart rate and oxygen pulse] were monitored, and ratings of perceived exertion obtained. Although there was a trend for the low-fitness group to have a higher plasma phosphate concentration prior to treatment ingestion, no treatment effects on plasma phosphate were noted at any sample time in either group. 2,3-DPG, VO2, oxygen pulse, VE, time to exhaustion and VO2max were significantly higher in the high-fitness group; however, no differences in these variables were observed as a result of phosphate ingestion. Plasma lactate was significantly lower in the high-fitness group during the submaximal exercise and the recovery period, but again phosphate ingestion had no effect. These results suggest that acute DCP supplementation is not effective as an ergogenic aid and that aerobic fitness level does not affect the response to phosphate supplementation.

2,3-Diphosphoglycerate↗

PubMed1996

The effects of induced alkalosis on the metabolic response to prolonged exercise in humans.

To examine the effects of alkalosis on the metabolic response to prolonged exercise, seven healthy males cycled for 1 h at approximately 70% of maximum oxygen uptake on two occasions, 1-week apart. Starting 3 h prior to exercise, subjects consumed either CaCO3 (placebo) or NaHCO3 (0.3 g.kg-1 body mass) over a 2-h period. Arterialised-venous blood samples were drawn before and during exercise for the determination of acid-base status and blood metabolites (lactate, glucose, glycerol and plasma free fatty acids). Expired gas was collected during exercise for determination of oxygen uptake (VO2) and respiratory exchange ratio to estimate fuel oxidation rates. Ratings of perceived exertion (RPE) and heart rates were also recorded. A significant (P < 0.01) alkalosis was observed at all times following bicarbonate ingestion. Blood lactate was significantly (P < 0.05) higher at all sample times throughout exercise following bicarbonate ingestion. Blood lactate concentration [mean (SEM)] reached peak values of 2.90 (0.16) and 4.24 (0.45) mmol.l-1 following 20 min of exercise following placebo and bicarbonate, respectively. No differences between treatments were noted at any time for the other metabolites. VO2 and RPE were significantly higher (P < 0.01) with the bicarbonate trial. At a constant power output increases in VO2 are generally associated with increases in fat oxidation, however, no evidence for an altered fuel oxidation was obtained in the present study. The differences in blood lactate indicate that induced alkalosis increased lactate efflux from muscle, but it cannot be confirmed whether this represents an increased rate of glycolysis within the muscle.

Adult↗

PubMed1994

Ergogenic effects of phosphate loading: physiological fact or methodological fiction?

Inorganic phosphate (Pi) supplementation has been reported to provide ergogenic benefits, though the research findings are inconsistent. Several confounding influences may explain these results, including mode of exercise, exercise intensity, dietary intake, daily biological fluctuations, type of supplement, administered dose of the supplement, washout period, length of loading period, fitness level of subjects, blood volume alterations, and sample collection and analysis techniques. This review provides a critical analysis of the methodological difficulties that may contribute to the equivocal research findings pertaining to Pi supplementation.

2,3-Diphosphoglycerate↗