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Biomedical subjects

T D Noakes

Publications and source records attributed to T D Noakes.

At least 163 records · Page 9Linked to original sources
PubMed1995

Anabolic-androgenic steroid increases running endurance in rats.

The study was designed to determine whether treatment with an anabolic-androgenic steroid enhances running performance in rats by increasing their freely chosen training distance. Forty male Long-Evans rats were randomly divided into either a sedentary control group or an exercising group caged in specially designed running wheels in which the rats were able to run spontaneously. After 4 wk, both groups were further subdivided into two groups receiving either 0.5-mg Durabolin (nandrolone phenylpropionate) (im) or 0.5-mg saline, every second day. After 8 wk, running distance was similar in both exercising groups. Rats receiving the anabolic-androgenic steroid ran 41% longer during the test of submaximal running endurance compared to the trained rats receiving saline (P < 0.05). Submaximal running endurance was not increased in sedentary rats receiving the anabolic-androgenic steroid. After 4 wk of training, the maximal sprinting speed increased by 29% in trained rats. There was no further increase in maximal sprinting speed after an additional 4 wk of training and treatment with either anabolic-androgenic steroid or saline treatment. Therefore, rats that train spontaneously while being treated with an anabolic-androgenic steroid had increased submaximal running endurance compared with trained rats treated with saline, despite the similar voluntary training distance and skeletal muscle oxidative capacity between the two groups. The mechanism by which treatment with an anabolic-androgenic steroid, combined with training, enhances submaximal running performance could not be identified and needs to be addressed in future studies.

Anabolic Agents↗
PubMed1995

The prevalence and significance of post-exercise (postural) hypotension in ultramarathon runners.

A consistent finding in exercise-associated collapse is a marked postural fall in the systolic blood pressure associated with a tachycardia. The prevalence and significance of these post-exercise (postural) changes in blood pressure among noncollapsed ultradistance athletes has not been well documented. The aim of this study was to compare pre- and post-race changes in systolic and diastolic blood pressures with changes in body weight and plasma volume and with symptoms of post-exercise hypotension, including the effects of posture, among a group of 31 runners competing in an 80-km footrace. During the race, runners developed a mean (+/- SD) weight loss of 3.5 (+/- 1.2) kg and plasma volume change of 12.8% (+/- 9.1). Asymptomatic postural hypotension defined as a fall in systolic blood pressure of greater than 20 mm Hg from the supine to the erect position without syncopal symptoms was present in two runners (7%) before the race and in 21 runners (68%) afterward. The degree of postural variation in systolic blood pressure was unrelated to changes in body weight or a fall in plasma volume. We conclude that (i) all runners were dehydrated by the race activity with a range of 1% to 7% and an average of 4.6%; (ii) asymptomatic post-exercise (postural) hypotension developed in the majority (68%) of ultramarathon runners in this study; (iii) the post-exercise hypotension is likely of multifactorial origin and is not entirely related to whole body dehydration or a reduction in plasma volume; and (iv) despite marked levels of dehydration among our sample of runners, their cardiovascular status in the supine position was not greatly compromised.

Adult↗
PubMed1994

Implications of a diagnosis of anorexia nervosa in a ballet school.

Competitive pressures to achieve a slim body shape may be of importance in the etiology of eating disorders in ballet dancers. This study examines the presence of anorexia nervosa-like symptoms in a group of 49 female ballet students (mean age = 18.9 years, SD +/- 1.9). All students were assessed for certain physical (weight and height) and psychological (Eating Attitude Test [EAT]) indices at the start of their academic training year. Thereafter, all subjects who presented with anorexia nervosa-like symptoms (EAT > or = 30, and/or with current secondary amenorrhea or primary amenorrhea if aged 16 years or over) at the initial assessment, were invited for a semistructured interview (Morgan-Russel scales) to determine their diagnostic status. Another aim of the study was to assess the prognostic implications of a diagnosis of anorexia nervosa in this sample. All subjects previously interviewed were invited for a follow-up assessment at 10 months. Anorexia nervosa could be diagnosed in 2 students (4.1%), whilst another 4 students (8.2%) presented with "partial syndrome" anorexia nervosa. All diagnosed students managed to complete their academic training year. The development and implications of a diagnosis of anorexia nervosa in the ballet students are discussed.

Adolescent↗
PubMed1994

Glucose kinetics during prolonged exercise in euglycaemic and hyperglycaemic subjects.

To determine the limits to oxidation of exogenous glucose by skeletal muscle, the effects of euglycaemia (plasma glucose 5 mM, ET) and hyperglycaemia (plasma glucose 10 mM, HT) on fuel substrate kinetics were evaluated in 12 trained subjects cycling at 70% of maximal oxygen uptake (VO2, max) for 2 h. During exercise, subjects ingested water labelled with traces of U-14C-glucose so that the rates of plasma glucose oxidation (Rox) could be determined from plasma 14C-glucose and expired 14CO2 radioactivities, and respiratory gas exchange. Simultaneously, 2-3H-glucose was infused at a constant rate to estimate rates of endogenous glucose turnover (Ra), while unlabelled glucose (25% dextrose) was infused to maintain plasma glucose concentration at either 5 or 10 mM. During ET, endogenous liver glucose Ra (total Ra minus the rate of infusion) declined from 22.4 +/- 4.9 to 6.5 +/- 1.4 mumol/min per kg fat-free mass [FFM] (P < 0.05) and during HT it was completely suppressed. In contrast, Rox increased to 152 +/- 21 and 61 +/- 10 mumol/min per kg FFM at the end of HT and ET respectively (P < 0.05). HT (i.e., plasma glucose 10 mM) and hyperinsulinaemia (24.5 +/- 0.9 microU/ml) also increased total carbohydrate oxidation from 203 +/- 7 (ET) to 310 +/- 3 mumol/min per kg FFM (P < 0.0001) and suppressed fat oxidation from 51 +/- 3 (ET) to 18 +/- 2 mumol/min per kg FFM (P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Enhanced endurance in trained cyclists during moderate intensity exercise following 2 weeks adaptation to a high fat diet.

These studies investigated the effects of 2 weeks of either a high-fat (HIGH-FAT: 70% fat, 7% CHO) or a high-carbohydrate (HIGH-CHO: 74% CHO, 12% fat) diet on exercise performance in trained cyclists (n = 5) during consecutive periods of cycle exercise including a Wingate test of muscle power, cycle exercise to exhaustion at 85% of peak power output [90% maximal oxygen uptake (VO2max), high-intensity exercise (HIE)] and 50% of peak power output [60% VO2max, moderate intensity exercise (MIE)]. Exercise time to exhaustion during HIE was not significantly different between trials: nor were the rates of muscle glycogen utilization during HIE different between trials, although starting muscle glycogen content was lower [68.1 (SEM 3.9) vs 120.6 (SEM 3.8) mmol.kg-1 wet mass, P < 0.01] after the HIGH-FAT diet. Despite a lower muscle glycogen content at the onset of MIE [32 (SEM 7) vs 73 (SEM 6) mmol.kg-1 wet mass, HIGH-FAT vs HIGH-CHO, P < 0.01], exercise time to exhaustion during subsequent MIE was significantly longer after the HIGH-FAT diet [79.7 (SEM 7.6) vs 42.5 (SEM 6.8) min, HIGH-FAT vs HIGH-CHO, P < 0.01]. Enhanced endurance during MIE after the HIGH-FAT diet was associated with a lower respiratory exchange ratio [0.87 (SEM 0.03) vs (SEM 0.02), P < 0.05], and a decreased rate of carbohydrate oxidation [1.41 (SEM 0.70) vs 2.23 (SEM 0.40) g CHO.min-1, P < 0.05].(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxybutyric Acid↗
PubMed1994

Effects of glucose ingestion or glucose infusion on fuel substrate kinetics during prolonged exercise.

To determine if bypassing both intestinal absorption and hepatic glucose uptake by intravenous glucose infusion might increase the rate of muscle glucose oxidation above 1 g.min-1, ten endurance-trained subjects were studied during 125 min of cycling at 70% of peak oxygen uptake (VO2peak). During exercise the subjects ingested either a 15 g.100 ml-1 U-14C labelled glucose solution or H2O labelled with a U-14C glucose tracer for the determination of the rates of plasma glucose oxidation (Rox) and exogenous carbohydrate (CHO) oxidation from plasma 14C glucose and 14CO2 specific activities, and respiratory gas exchange. Simultaneously, 2-3H glucose was infused at a constant rate to measure glucose turnover, while unlabelled glucose (25% dextrose) was infused into those subjects not ingesting glucose to maintain plasma glucose concentration at 5 mmol.l-1. Despite similar plasma glucose concentrations [ingestion 5.3 (SEM 0.13) mmol.l-1; infusion 5.0 (0.09) mmol.l-1], compared to glucose infusion, CHO ingestion significantly increased plasma insulin concentrations [12.9 (1.0) vs 4.8 (0.5) mU.l-1; P < 0.05], raised total Rox values [9.5 (1.2) vs 6.2 (0.7) mmol.125 min-1 kg fat free mass-1 (FFM); P < 0.05] and rates of CHO oxidation [37.2 (2.8) vs 24.1 (3.9) mmol.125 min-1 kg FFM-1; P < 0.05]. An increased reliance on CHO metabolism with CHO ingestion was associated with a decrease in fat oxidation. Whereas the contribution from fat oxidation to energy production increased to 51 (10)% with glucose infusion, it only reached 18 (4)% with glucose ingestion (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1994

Impaired high-intensity cycling performance time at low levels of dehydration.

On two separate occasions six trained subjects (peak oxygen consumption [VO2peak] 4.41/min) rode for 60 min at 70% of VO2peak and then to exhaustion at 90% of VO2peak to determine the effects of mild dehydration on high-intensity cycling performance time in the heat (32 degrees C, 60% relative humidity, wind speed 3 km/h). In one trial (F) subjects ingested a 400 ml bolus of 20 mmol/l NaCl immediately before, and then as repetitive 120 ml feedings every 10 min during the first 50 min of exercise. In the other trial they did not ingest fluid (NF) either before or during exercise. The order of testing was in a counter-balanced random sequence. For the first 60 min of exercise mean (+/- SD) VO2 (2.90 +/- 0.39 vs 2.93 +/- 0.38 l/min) and respiratory exchange ratio (RER; 0.95 +/- 0.03 vs 0.94 +/- 0.04) values were similar between F and NF trials. However, weight loss was significantly reduced during F compared to NF (0.16 +/- 0.39 vs 1.30 +/- 0.22 kg; p < 0.005) and high-intensity cycling time to exhaustion was significantly increased (9.8 +/- 3.9 vs 6.8 +/- 3.0 min; p < 0.005). Increased cycling times to exhaustion in the F trial were not associated with any measurable differences in heart rate (HR), body temperature, respiratory gas exchange, leg muscle power over 5 sec, or the degree to which fluid ingestion reduced the level of dehydration within the group. Only the ratings of perceived exertion (RPE) and plasma anti diuretic hormone (ADH) concentrations were significantly increased in the NF trial compared to the F trial.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Carbohydrate, fluid, and electrolyte requirements of the soccer player: a review.

Soccer requires field players to exercise repetitively at high intensities for the duration of game, which can result in marked muscle glycogen depletion and hypoglycemia. A soccer match places heavy demands on endogenous muscle and liver glycogen stores and fluid reserves, which must be rapidly replenished when players complete several matches within a brief period of time. Low concentrations of muscle glycogen have been reported in soccer players before a game, and daily carbohydrate (CHO) intakes are often insufficient to replenish muscle glycogen stores. CHO supplementation during soccer matches has been found to result in muscle glycogen sparing (39%), greater second-half running distances, and more goals being scored with less conceded, when compared to consumption of water. Thus, CHO supplementation has been recommended prior to, during, and after matches. In contrast, there is currently insufficient evidence to recommend without reservation the addition of electrolytes to a beverage for ingestion by players during a game resulting in sweat losses of < 4% of body weight.

Dietary Carbohydrates↗
PubMed1994

Influence of carbohydrate ingestion on fuel substrate turnover and oxidation during prolonged exercise.

This study examined effects of ingesting a 10% carbohydrate (CHO) drink (CI) or placebo (PI) at 500 ml/h on total (splanchnic) glucose appearance (endogenous+exogenous; Ra), blood glucose oxidation, and muscle glycogen utilization in 14 male endurance-trained cyclists who rode for 180 min at 70% of maximal O2 uptake after CHO loading [starting muscle glycogen 203 +/- 7 (SE) mmol/kg wet wt]. Total CHO oxidation was similar in CI and PI, but Ra increased significantly during the trial in both groups with CI reaching a plateau after 75 min. Ra was significantly greater in CI than in PI at the end of exercise. Blood glucose oxidation also increased significantly during the trial to a plateau in CI and was significantly higher in CI than in PI at the end of exercise. However, mean endogenous Ra was significantly lower in CI than in PI throughout exercise, as was oxidation of endogenous blood glucose, which remained almost constant in CI and reached 43 +/- 8 and 73 +/- 13 mumol.min-1.kg fat-free mass-1 in CI and PI, respectively, at the end of exercise. At 0.83 g/min of CHO ingestion, 0.77 +/- 0.03 g/min was oxidized. Muscle glycogen utilization was identical in both groups and was higher during the 1st h of exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Enhanced adipose tissue lipoprotein lipase activity in detrained rats: independent of changes in food intake.

Short-term detraining has been characterized by increased body mass and rapid body fat accretion. However, detraining has also been associated with increased food intake, especially in rats genetically predisposed to obesity. Thus, it has been difficult to separate refeeding effects from alterations resulting from the cessation of exercise training. In the present study, the in vitro activity of adipose tissue lipoprotein lipase (ATLPL) was measured in freely running wheel-trained rats and rats that had stopped training for 1, 2, or 3 days or 1 or 2 wk, respectively. Heparin-releasable ATLPL activity was measured at rest and after acute exhaustive exercise. Feeding efficiency (change in body mass/kJ ingested energy), fat pad mass, and adipocyte size were also measured. The rate of weight gain in 1- and 2-wk detrained rats was significantly higher than that of sedentary control or trained rats (P < 0.05). Feeding efficiency was also higher in 1-wk detrained rats than in all other groups (P < 0.005). However, food energy intake was not different between trained rats, 1- and 2-wk detrained rats, or sedentary control rats. ATLPL activity in all groups was highest after acute exhaustive exercise. ATLPL activity in 1-wk detrained rats was nearly threefold higher compared with that in trained rats (P < 0.005) and was not different from that of sedentary control rats. These results suggest that the cessation of exercise training causes an enhanced capacity for lipogenesis independent of changes in food energy intake or the acute effects of the last bout of exercise.

Adipocytes↗
PubMed1994

Drugs in sport.

Explore the source record for details and available documents.

Doping in Sports↗
PubMed1994

Heart rate responses during a 4-d cycle stage race.

The purpose of this study was to monitor the heart rates (HR) of seven, well-trained (maximal oxygen uptake [VO2max] 5.0 +/- 0.5 l.min-1), competitive cyclists during a 4-d cycle stage race. On consecutive days, subjects competed in a 16.0-km individual time trial (TT), a 110.0-km mass-start road race (RR1), a 5.5-km individual hill climb (HC), and a 105.0-km mass-start road race (RR2). Within 10 d of the final race, cyclists underwent a test to determine VO2max, peak power output, and maximal HR. Comparison of the HR responses to each race revealed that the individual events were performed at a relatively high and constant work rate (91.1 +/- 2.5% and 93.2 +/- 4.7% of the maximal HR as measured in the field (HRmax) for the TT and HC, respectively). In contrast, despite similar racing speeds (42.2 +/- 1.0, 39.9 +/- 0.2, and 40.6 +/- 0.5 km.h-1 for the TT, RR1, and RR2, respectively), the HR responses to the longer mass-start races were reduced to 81.9 +/- 9.6% and 78.6 +/- 8.9% of HRmax and were random in frequency and amplitude. Such stochastic changes in HR were seemingly unrelated to course terrain but may be due to the group dynamics of the cyclists. The results of this study reveal the stochastic nature of bunch cycle racing and show that the HR responses of competitive cyclists are more a function of tactical bunch riding than of terrain.

Bicycling↗
PubMed1994

Clinical and biochemical characteristics of collapsed ultra-marathon runners.

To evaluate the characteristics of runners with exercise-associated collapse (EAC), we studied the time of onset of collapse, rectal temperatures, cardiovascular status, and incidence of readily identifiable medical conditions in 46 male athletes who collapsed during or after a 56-km ultramarathon footrace run on a cool day. Data were compared with 65 control runners who did not collapse in the same race. Weight changes during recovery were studied in a subsample of both groups. The majority (85%) of runners with EAC collapsed after they had completed the race; rectal temperatures (38.5 +/- 1.3 degrees C, mean +/- SD; range 35.5-42.0 degrees C) and supine heart rates (87.5 +/- 17.2 min-1; range 60-138) were only modestly elevated. Postrace serum sodium concentrations, changes in plasma volume, and mass during recovery were not significantly different from values in control runners. We conclude that: (i) most cases of EAC (85%) occur after the finish line; (ii) runners collapsing during the race are more likely to have a readily identifiable medical condition than runners collapsing after the finish line; (iii) runners collapse most frequently near cutoff times for medals and race closure times; and (iv) 16% of EAC casualties and 19% of control runners have identifable biochemical abnormalities.

Adult↗
PubMed1994

Level of physical activity and CHD risk factors in black South African men.

Coronary heart disease (CHD) is uncommonly low among black South Africans. Although dietary and genetic influences probably contribute to their favorable serum lipid profile, other cardioprotective factors may also play a significant role in explaining the low incidence of CHD. From a socioeconomic perspective, it appears that the black community engages in regular physical activity (PA) more so than other populations. Since data are lacking, our aim was to provide preliminary data on the association between PA and the traditional CHD risk factors. The sample consisted of 212 working, middle-aged men drawn from an epidemiological database on the African population of metropolitan Cape Town. Analysis of responses to basic questions on PA behavior indicated i) 43% of the sample were employed in jobs requiring moderate to strenuous PA, and ii) the most favorable blood pressure and serum lipid profiles were associated with low to moderate levels of habitual exercise. As this community becomes more urbanized, job-related PA as well as PA of daily living will decline. The need for sports and leisure-time PA programs will become more important and should be considered as part of a public health strategic plan.

Adult↗
PubMed1993

Chronic beta-blockade does not influence muscle power output during high-intensity exercise of short-duration.

Patients receiving beta-receptor antagonists for the treatment of hypertension frequently complain of impaired exercise tolerance. To determine whether these medications impair skeletal muscle contractile function, we measured isokinetic muscle function in ten healthy male cyclists receiving nebivolol (N), atenolol (A), propranolol (P) and the calcium channel antagonist diltiazem (D). The subjects performed standardized tests of muscle power on an isokinetic cycle ergometer following subacute ingestion of N, A, P, D and placebo (PL) in a double blind crossover trial. Subjects exercised maximally for 10 s at 90, 110, 120, 130 and 150 rpm with 2-min rest between sessions. Thereafter, they performed a 30-s fatigue test at 120 rpm. Resting heart rate was decreased 13.4%, 21.9% and 14.6% by N, A and P, respectively (P < 0.05 vs PL). Resting systolic blood pressure was decreased 6.7% by A only (P < 0.05 vs PL). Peak power, average power and work done was not different among treatment groups at any crank velocity, nor was there any difference in total work done or rate of work decline in the 30-s test. We concluded from our study that peak isokinetic muscle power during maximal exercise of short duration is not affected by beta-blockade or the calcium antagonist diltiazem. Fatigue during beta-receptor antagonism would not appear therefore to be due to changes in the ability of skeletal muscle to produce peak power output during exercise of short duration.

Adrenergic beta-Antagonists↗