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Biomedical subjects

T D Noakes

Publications and source records attributed to T D Noakes.

At least 19 recordsLinked to original sources
PubMed1992

Crystalluria in marathon runners. IV. Black subjects.

Crystal sizes (scanning electron microscopy) and distributions (Coulter Counter) as well as 24-h urinary sodium (Na) and calcium (Ca) excretions (flame atomic absorption) were determined in a group of black South African runners immediately after a marathon and again 3 weeks later. White runners and black and white control subjects were included in the study. Particle volume-size histograms for black controls and black runners were identical. There was no significant difference in the Na excretion of all the groups. However, while urinary Ca excretion was significantly raised in white runners relative to white controls, Ca excretion in black runners was unchanged relative to their controls. It is postulated that the lower rates of urinary Ca excretion may result from lower rates of Ca resorption from bone in response to the cyclical loading of running in black marathon runners. The results of this study suggest that black marathon runners are not prone to the same increased risk of renal stone formation as are white runners.

Adult↗
PubMed1992

Oxidation of exogenous carbohydrate during prolonged exercise: the effects of the carbohydrate type and its concentration.

We studied rates of exogenous carbohydrate (CHO) oxidation during 90 min of cycling exercise in trained cyclists exercising at 70% of maximal oxygen consumption (VO2max) when they ingested glucose, sucrose, or glucose polymer solutions at concentrations of 7.5%, 10% or 15%. Drinks were labelled with [U-14C]glucose or sucrose and were ingested at a rate of 100 ml.10 min-1. Rates of oxidation of the ingested CHO were calculated from the specific radio-activity of the labelled CHO, expired 14CO2 and carbon dioxide output (VCO2). Total CHO oxidation, determined from oxygen consumption and VCO2 was not influenced by CHO type or concentration. Gastric emptying (P = 0.01) and the rate of exogenous CHO oxidation (P = 0.028) was greatest for the glucose polymer solutions, and least for glucose. Although gastric emptying (P = 0.006) decreased with increasing CHO concentration, CHO delivery to the intestine and exogenous CHO oxidation increased linearly with increasing CHO concentration. The percentage of the CHO delivered to the intestine that was oxidized ranged from 30.0% for 7.5% CHO to 38.1% for 15% CHO. Our results indicated that the rate of gastric emptying for CHO was not controlled to provide a constant rate of energy delivery as is commonly believed and that factors subsequent to gastric emptying limit the rate of exogenous CHO oxidation from the ingested solution.

Adult↗
PubMed1992

Oxygen delivery does not limit peak running speed during incremental downhill running to exhaustion.

Oxygen consumption (VO2), ventilation (VI), respiratory exchange ratio (R), stride frequency and blood lactate concentrations were measured continuously in nine trained athletes during two continuous incremental treadmill runs to exhaustion on gradients of either 0 degree or -3 degrees. Compared to the run at 0 degree gradient, the athletes reached significantly higher maximal treadmill velocities but significantly lower VO2, VI, R and peak blood lactate concentrations (P less than 0.001) during downhill running. These lower VO2 and blood lactate concentrations at exhaustion indicated that factors other than oxygen delivery limited maximal performance during the downhill run. In contrast, stride frequencies were similar at each treadmill velocity; the higher maximal speed during the downhill run was achieved with a significantly longer stride length (P less than 0.001); maximal stride frequency was the same between tests. Equivalent maximal stride frequencies suggested that factors determining the rate of lower limb stride recovery may have limited maximal running speed during downhill running and, possibly, also during horizontal running.

Adult↗
PubMed1992

Exogenous carbohydrate oxidation from maltose and glucose ingested during prolonged exercise.

Intestinal perfusion studies have shown that glucose absorption from maltose occurs faster than from isocaloric glucose. To determine whether ingested maltose might be a superior source of carbohydrate (CHO) for endurance athletes, we compared the rates of gastric emptying, absorption and oxidation of 15 g.100 ml-1 solutions of maltose and glucose. Six endurance-trained cyclists drank 1200 ml of either U-14C maltose or U-14C glucose as a 400-ml loading bolus immediately before exercise, and as 8 x 100-ml drinks at 10-min intervals during a 90-min ride at 70% of maximal oxygen consumption. The rates of gastric emptying [maltose 690 (SD 119) ml.90 min-1; glucose 655 (SD 93) ml.90 min-1], the appearance of U-14C label in the plasma, and the peak rates of exogenous CHO oxidation [maltose 1.0 (SD 0.09) g.min-1; glucose 0.9 (SD 0.09) g.min-1] were not significantly different. Further, the 51 (SD 8) g of maltose and the 49 (SD 9) g of glucose oxidised during exercise were similar. Each accounted for approximately 20% of the total CHO oxidised during the 90 min of exercise. Since only half of the CHO delivered to the intestine was oxidised in the 90-min ride (maltose 49%; glucose 50%), we conclude that neither the rate of gastric emptying, nor digestion limited the rate of ingested CHO utilisation during the early stages of exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Peak power output predicts maximal oxygen uptake and performance time in trained cyclists.

The purposes of this study were firstly to determine the relationship between the peak power output (Wpeak) and maximal oxygen uptake (VO2max) attained during a laboratory cycling test to exhaustion, and secondly to assess the relationship between Wpeak and times in a 20-km cycling trial. One hundred trained cyclists (54 men, 46 women) participated in the first part of this investigation. Each cyclist performed a minimum of one maximal test during which Wmax and VO2max were determined. For the second part of the study 19 cyclists completed a maximal test for the determination of Wpeak, and also a 20-km cycling time trial. Highly significant relationships were obtained between Wpeak and VO2max (r = 0.97, P less than 0.0001) and between Wpeak and 20-km cycle time (r = -0.91, P less than 0.001). Thus, Wpeak explained 94% of the variance in measured VO2max and 82% of the variability in cycle time over 20 km. We concluded that for trained cyclists, the VO2max can be accurately predicted from Wpeak, and that Wpeak is a valid predictor of 20-km cycle time.

Adult↗
PubMed1992

'Sports anemia'--a real or apparent phenomenon in endurance-trained athletes?

In order to critically define the apparently widespread condition 'sports anemia', the red cell indices and iron status of male distance runners and triathletes, and female distance runners and ballet dancers were compared to non-exercising controls of both sexes. The mean hemoglobin (Hb) levels of all groups were within the normal ranges and there was no difference between the athletic and control groups of each sex. The mean serum ferritin (SF) concentration of the male distance runners (79.8 micrograms/l) was significantly lower than that of the triathletes (123.5 micrograms/l) and controls (138.3 micrograms/l). Iron deficiency (SF less than 12 micrograms/l, % saturation less than 18%) was evident in 3.3% and 5% of the male and female runners respectively, and 3.3% of the ballet dancers. Iron deficiency anemia (abnormal red cell indices and iron status) occurred in only 1.7% and 3.3% of the male and female distance runners respectively, and 3.3% of the dancers. However, 7 (11.7%) each of the male and female distance runners and 6 (20.0%) of the ballet dancers recorded hemoglobin values lower than the normal range of 140 g/l and 120 g/l for males and females respectively. This anomaly can be explained by a significantly expanded plasma volume in endurance-trained individuals, causing a 'pseudoanemia'. We conclude therefore that athletes are at no greater risk for developing a frank anemia than the non-exercising population, and that the term 'sports anemia' is misleading, as it does not describe a specific clinical entity.

Adolescent↗
PubMed1992

Dietary iron deficiency and sports anaemia.

In order to determine whether dietary inadequacies can explain the sub-optimal iron status widely documented in endurance-trained athletes, the food intake records of Fe-deficient and Fe-replete distance runners and non-exercising controls of both sexes were analysed. In all the male study groups the mean dietary Fe intake met the recommended dietary allowances (RDA; > 10 mg/d (US) Food and Nutrition Board, 1989). However, both female athletes and controls failed to meet the RDA with regard to Fe (< 15 mg/d) and folate (< 200 micrograms/d). There was no difference in the total Fe intakes of Fe-deficient and Fe-replete athletes and the controls of each sex. However, Fe-deficient male runners, but not female runners, consumed significantly less haem-Fe (P = 0.048) than their comparative groups. This suggests that the habitual consumption of Fe-poor diets is a factor in the aetiology of athletes' Fe deficiency.

Adult↗
PubMed1992

Ventilation and blood lactate increase exponentially during incremental exercise.

This study examined whether the ventilatory (V) compensation for metabolic acidosis with increasing O2 uptake (VO2) and CO2 output (VCO2) might be more in accord with the theoretical expectation of a progressive acceleration of proton production from carbohydrate oxidation rather than a sudden onset of blood lactate (BLa) accumulation. The interrelationships between V, VO2, VCO2 and BLa concentration, [BLa], were investigated in 10 endurance-trained male cyclists during incremental (120 +/- 15 W min-1) exercise tests to exhaustion. Regression analyses on the V, VCO2 and [BLa] vs VO2 data revealed that all were better fitted by continuous Y = A.exp.[B.VO2] + C rate laws than by threshold linear rate equations (P < 0.0001). Plots of V vs VCO2 and [BLa] were also non-linear. Ventilation increased as an exponential V = 27 +/- 4.exp.[0.37 +/- 0.03.VCO2] function of VCO2 and as a hyperbolic function of [BLa]. In opposition to the 'anaerobic (lactate) threshold' hypothesis, we suggest these data are more readily explained by a continuous development of acidosis, rather than a sudden onset of BLa accumulation, during progressive exercise.

Acidosis↗
PubMed1992

Failure of magnesium supplementation to influence marathon running performance or recovery in magnesium-replete subjects.

This study examined the effect of magnesium supplementation on muscle magnesium content, on running performance during a 42-km marathon footrace, and on muscle damage and the rate of recovery of muscle function following the race. Twenty athletes were divided equally into two matched groups and were studied for 4 weeks before and 6 weeks after a marathon in a double-blind trial; the experimental group received magnesium supplement (365 mg per day) and the control group, placebo. Magnesium supplementation did not increase either muscle or serum magnesium concentrations and had no measurable effect on 42-km marathon running performance. Extra magnesium ingestion also had no influence on the extent of muscle damage or the rate of recovery of muscle function. The latter was significantly reduced immediately after the marathon but returned to normal within 1 week. Thus, magnesium supplementation in magnesium-replete subjects did not enhance performance or increase resistance to muscle damage during the race, or the rate of recovery of muscle function following the race.

Adult↗
PubMed1992

The hyponatremia of exercise.

The hyponatremia of exercise may exist in symptomatic and asymptomatic forms. Symptomatic hyponatremia is usually characterized by severe alterations in cerebral function including coma and grand mal seizures; it develops especially in less competitive athletes who have maintained high rates of fluid intake during endurance events lasting at least 5 hours. The hyponatremia becomes symptomatic when the volume of excess fluid retained exceeds 2 to 3 liters. The etiology of the condition is unknown. Possibly as many as three or more pathologies (abnormal fluid retention possibly due to inappropriate ADH secretion, abnormal regulation of the extracellular fluid volume, translocation of sodium into a "third space") must be present for symptomatic hyponatremia to develop. The avoidance of overhydration would appear to be the only certain way that susceptible individuals can prevent symptomatic hyponatremia. Sodium chloride containing solutions ingested in physiologically significant concentrations would likely prevent a possible "third space" effect.

Adult↗
PubMed1992

Effects of training on lactate production and removal during progressive exercise in humans.

To determine whether the reduced blood lactate concentrations [La] during submaximal exercise in humans after endurance training result from a decreased rate of lactate appearance (Ra) or an increased rate of lactate metabolic clearance (MCR), interrelationships among blood [La], lactate Ra, and lactate MCR were investigated in eight untrained men during progressive exercise before and after a 9-wk endurance training program. Radioisotope dilution measurements of L-[U-14C]lactate revealed that the slower rise in blood [La] with increasing O2 uptake (VO2) after training was due to a reduced lactate Ra at the lower work rates [VO2 less than 2.27 l/min, less than 60% maximum VO2 (VO2max); P less than 0.01]. At power outputs closer to maximum, peak lactate Ra values before (215 +/- 28 mumol.min-1.kg-1) and after training (244 +/- 12 mumol.min-1.kg-1) became similar. In contrast, submaximal (less than 75% VO2max) and peak lactate MCR values were higher after than before training (40 +/- 3 vs. 31 +/- 4 ml.min-1.kg-1, P less than 0.05). Thus the lower blood [La] values during exercise after training in this study were caused by a diminished lactate Ra at low absolute and relative work rates and an elevated MCR at higher absolute and all relative work rates during exercise.

Adult↗
PubMed1992

Oxidation of carbohydrate ingested during prolonged endurance exercise.

Classic studies conducted in the 1920s and 1930s established that the consumption of a high carbohydrate (CHO) diet before exercise and the ingestion of glucose during exercise delayed the onset of fatigue, in part by preventing the development of hypoglycaemia. For the next 30 to 40 years, however, interest in CHO ingestion during exercise waned. Indeed, it was not until the reintroduction of the muscle biopsy technique into exercise physiology in the 1960s that a series of studies on CHO utilisation during exercise appeared. Investigations by Scandinavian physiologists showed that muscle glycogen depletion during prolonged exercise coincided with the development of fatigue. Despite this finding, attempts to delay fatigue during prolonged exercise focused principally on techniques that would increase muscle glycogen storage before exercise. The possibility that CHO ingestion during exercise might also delay the development of muscle glycogen depletion and hence, at least potentially, fatigue, was not extensively investigated. This, in part, can be explained by the popular belief that water replacement to prevent dehydration and hyperthermia was of greater importance than CHO replacement during prolonged exercise. This position was strengthened by studies in the early 1970s which showed that the ingestion of CHO solutions delayed gastric emptying compared with water, and might therefore exacerbate dehydration. As a result, athletes were actively discouraged from ingesting even mildly concentrated (greater than 5 g/100ml) CHO solutions during exercise. Only in the early 1980s, when commercial interest in the sale of CHO products to athletes was aroused, did exercise physiologists again begin to study the effects of CHO ingestion during exercise. These studies soon established that CHO ingestion during prolonged exercise could delay fatigue; this finding added urgency to the search for the optimum CHO type for ingestion during exercise. Whereas in the earlier studies, estimates of CHO oxidation were made using respiratory gas exchange measurements, investigations since the early 1970s have employed stable 13C and radioactive 14C isotope techniques to determine the amount of ingested CHO that is oxidised during exercise. Most of the early interest was in glucose ingestion during exercise. These studies showed that significant quantities of ingested glucose can be oxidised during exercise. Peak rates of glucose oxidation occur approximately 75 to 90 minutes after ingestion and are unaffected by the time of glucose ingestion during exercise. Rates of oxidation also appear not to be influenced to a major extent by the use of different feeding schedules.(ABSTRACT TRUNCATED AT 400 WORDS)

Dietary Carbohydrates↗
PubMed1992

The effects of antihypertensive medications on the physiological response to maximal exercise testing.

This study compared the effects of clinically prescribed doses of cilazapril, nifedipine, and atenolol on maximal exercise performance in physically active subjects. In a double-blind crossover trial, 10 healthy male volunteers performed progressive aerobic exercise to exhaustion for determination of maximal oxygen consumption (VO2 max), after single dose ingestion of cilazapril, nifedipine, atenolol, and placebo. Measurements were made at exhaustion and at a single submaximal workload (250 W). Exercise time to exhaustion and peak workload were decreased by all agents (p less than 0.05 vs. placebo), but VO2 max was decreased by atenolol only (p less than 0.05 vs. placebo). Although both atenolol and cilazapril decreased the maximum systolic blood pressure, the peak heart rate was decreased only by atenolol (p less than 0.001 vs. placebo). Whereas submaximal oxygen consumption, minute ventilation, and blood lactate concentrations were not different between groups, ratings of perceived exertion were increased during submaximal exercise by atenolol and cilazapril (p less than 0.05 vs. placebo). Cilazapril, nifedipine, and atenolol all impaired exercise performance and increased ratings of perceived exertion during submaximal exercise without altering rates of oxygen consumption or blood lactate accumulation. Maximal exercise performance was impaired to a greater extent by atenolol than by nifedipine or cilazapril. This study suggests that either angiotensin-converting enzyme inhibitors or calcium-channel antagonists might be preferable for the management of hypertension in athletic patients as they have a lesser effect on exercise performance, at least in healthy individuals.

Adult↗
PubMed1991

A retrospective study of spinal cord injuries in Cape Province rugby players, 1963-1989. Incidence, mechanisms and prevention.

A retrospective study was undertaken to determine aetiological factors for 117 catastrophic neck injuries in rugby players admitted to the Spinal Cord Unit, Conradie Hospital, Cape Town, between 1963 and 1989. Nineteen of these players were known to be dead; the files of another 10 were missing. Questionnaires were sent to the remaining 88 players and 52 responded (59%). Their data were supplemented with information obtained from the medical records of the patients who did not respond. The annual number of admissions increased dramatically after 1976 with 83% of all injuries occurring after that date. A further increase since 1984 contrasts with a falling incidence of these injuries in Britain, Australia and New Zealand. Increased risk of injury was related to the following factors: 98% of injuries occurred in matches and 81% were incurred by adults; 69% of injuries occurred in age-group A team or senior first team players; and 57% of injuries occurred in the tackle situation and 39% in scrums, rucks and mauls. Hooker, centre and flyhalf were the playing positions at greatest risk. Injuries were more common in early season matches and again after the mid-season break. This study confirmed that spinal cord injuries occur under predictable circumstances and are therefore foreseeable and preventable. The high incidence of these injuries in the Cape Province is as unacceptable today as it was when first reported in 1977.

Adolescent↗
PubMed1991

Anti-inflammatory and combined anti-inflammatory/analgesic medication in the early management of iliotibial band friction syndrome. A clinical trial.

Forty-three athletes presenting with unilateral iliotibial band friction syndrome (ITBFS) were randomly divided into three groups for the first 7 days of treatment (placebo-controlled, double-blind): 1--placebo (N = 13); 2--anti-inflammatory medication (N = 14) (Voltaren; Geigy); and 3--analgesic/anti-inflammatory combined medication (N = 16) (Myprodol; Rio Ethicals). All subjects rested from day 0 to day 7 and all groups received the same physiotherapy outpatient treatment programme from day 3 to day 7. On days 0, 3 and 7 the subjects performed a functional treadmill running test (maximum 30 minutes) during which they reported pain (scale 0-10; 0 = no pain, 10 = unbearable pain) each minute. Total running distance, total running time and the area under the pain v. time curve was calculated. Daily 24-hour recall pain scores were also recorded. The 24-hour recall pain scores decreased significantly for all the groups over the treatment period. This method of assessing efficacy of treatment therefore failed to show differences between groups. In contrast, during the running test only group 3 improved their total running time and distance from day 0 to day 7, whereas in all the groups the area under the pain v. time curve decreased from day 0 to day 7. All the other groups improved total running time and running distance from day 3 to day 7. All three treatment modalities are effective in the early treatment of ITBFS but physiotherapy in combination with analgesic/anti-inflammatory medication is superior.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaminophen↗
PubMed1991

Crystalluria in marathon runners. III. Stone-forming subjects.

In order to investigate further the possible relationship between urinary stone formation and marathon running, the crystalluria in seven male, stone forming runners was characterized. Particle size distribution curves (Coulter counter) and crystal number, size and morphology (scanning electron microscopy) were measured. These studies suggest that urinary stone formation may be accelerated in those subjects with previous histories of renal stone formation but that the nature of the crystalluria is favourably affected by an increase in fluid intake. The presence of large quantities of mucoid material in the urine of "natural" stone formers and its absence in the urine of stone-forming runners is cited as evidence for the existence of different aetiological mechanisms in these groups. It is concluded that while natural stone formers may be at chronic risk of stone formation due to pathological factors, marathon runners may be at acute risk due to factors associated with long distance running itself.

Adult↗
PubMed1991

Evaluation of renal function and fluid homeostasis during recovery from exercise-induced hyponatremia.

Renal function including fluid and electrolyte balance was studied during recovery in eight subjects who developed symptomatic hyponatremia (HN; plasma sodium concentration less than 130 mM) during an 88-km ultramarathon footrace and compared with results for normonatremic runners [NN; n = 18, mean postrace plasma sodium concentration, 138.2 +/- 1.2 (SE) mM]. Estimated fluid intake during the race for HN was 12.5 +/- 1.6 (SE) liters over 9 h 41 min (+/- 28 min). HN excreted a net fluid excess of 2.95 +/- 0.56 (range 1.2-5.9) liters compared with a fluid deficit of 2.7 +/- 0.3% body weight in NN. The sodium deficit was 153 +/- 35 mmol in HN and 187 +/- 37 mmol in NN. Despite the fluid overload, plasma volume was decreased by 24.1 +/- 5.0% in HN compared with 8.2 +/- 2.6% in NN. Serum renin activity (5.1 +/- 2.0 ng.ml-1.h-1), aldosterone concentrations (410 +/- 34 ng/l), creatinine clearances (174.8 +/- 28.2 ml/min), and urine output (6.4 +/- 1.0 ml/min) were markedly elevated in HN during recovery. Thus the hyponatremia of exercise results from fluid retention in subjects who ingest abnormally large fluid volumes during prolonged exercise.

Adult↗