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Biomedical subjects

T D Noakes

Publications and source records attributed to T D Noakes.

At least 37 records · Page 2Linked to original sources
PubMed2004

The -55 C/T polymorphism within the UCP3 gene and performance during the South African Ironman Triathlon.

Uncoupling protein 3 is believed to be involved in total body energy expenditure, including the regulation of fat and glucose metabolism. These biochemical processes may distinguish top ultra-endurance triathletes from slower competitors. The aim of this study was to determine whether the uncoupling protein 3 gene is associated with the performance capacity of ultra-endurance Ironman triathletes. Two triathlete groups consisting of the 89 fastest and 89 slowest Caucasian, male triathletes who completed either the 2000 or 2001 South African Ironman triathlon events were genotyped for the -55 C/T polymorphism within the uncoupling protein 3 gene. A control group consisting of 92 Caucasian males who had not trained for or participated in an ultra-endurance athletic event was also genotyped. There was no significant difference in the genotype (CC, CT and TT) frequency distribution of the -55 C/T polymorphism within the uncoupling protein 3 gene between the fast triathlete, slow triathlete and control groups. In addition, no significant differences were observed between the frequencies of the C and T alleles between the three groups. The two triathlete groups were combined and grouped according to their genotype. No particular genotype or allele was associated with the time taken by the triathletes to complete the entire triathlon, or either the swim, cycle or run legs of the event. Thus no association was found between the -55 C/T polymorphism within the uncoupling protein 3 gene and the ultra-endurance performance of triathletes who completed either the 2000 or 2001 South African Ironman triathlons.

Alleles↗
PubMed2004

The dipsomania of great distance: water intoxication in an Ironman triathlete.

Of 371 athletes (62% of all finishers) whose weights were measured before and after the 226 km South African Ironman Triathlon, the athlete who gained the most weight (3.6 kg) during the race was the only competitor to develop symptomatic hyponatraemia. During recovery, he excreted an excess of 4.6 litres of urine. This case report again confirms that symptomatic hyponatraemia is caused by considerable fluid overload independent of appreciable NaCl losses. Hence prevention of the condition requires that athletes be warned not to drink excessively large volumes of fluid (dipsomania) during very prolonged exercise. This case report also shows that there is a delayed diuresis in this condition and that it is not caused by renal failure.

Adult↗
PubMed2004

Skeletal muscle pathology in endurance athletes with acquired training intolerance.

BACKGROUND: It is well established that prolonged, exhaustive endurance exercise is capable of inducing skeletal muscle damage and temporary impairment of muscle function. Although skeletal muscle has a remarkable capacity for repair and adaptation, this may be limited, ultimately resulting in an accumulation of chronic skeletal muscle pathology. Case studies have alluded to an association between long term, high volume endurance training and racing, acquired training intolerance, and chronic skeletal muscle pathology. OBJECTIVE: To systematically compare the skeletal muscle structural and ultrastructural status of endurance athletes with acquired training intolerance (ATI group) with asymptomatic endurance athletes matched for age and years of endurance training (CON group). METHODS: Histological and electron microscopic analyses were carried out on a biopsy sample of the vastus lateralis from 18 ATI and 17 CON endurance athletes. The presence of structural and ultrastructural disruptions was compared between the two groups of athletes. RESULTS: Significantly more athletes in the ATI group than in the CON group presented with fibre size variation (15 v 6; p = 0.006), internal nuclei (9 v 2; p = 0.03), and z disc streaming (6 v 0; p = 0.02). CONCLUSIONS: There is an association between increased skeletal muscle disruptions and acquired training intolerance in endurance athletes. Further studies are required to determine the nature of this association and the possible mechanisms involved.

Adult↗
PubMed2004

Serum electrolyte concentrations and hydration status are not associated with exercise associated muscle cramping (EAMC) in distance runners.

OBJECTIVES: To determine whether acute exercise associated muscle cramping (EAMC) in distance runners is related to changes in serum electrolyte concentrations and hydration status. METHODS: A cohort of 72 runners participating in an ultra-distance road race was followed up for the development of EAMC. All subjects were weighed before and immediately after the race. Blood samples were taken before the race, immediately after the race, and 60 minutes after the race. Blood samples were analysed for glucose, protein, sodium, potassium, calcium, and magnesium concentrations, as well as serum osmolality, haemoglobin, and packed cell volume. Runners who suffered from acute EAMC during the race formed the cramp group (cramp, n = 21), while runners with no history of EAMC during the race formed the control group (control, n = 22). RESULTS: There were no significant differences between the two groups for pre-race or post-race body weight, per cent change in body weight, blood volume, plasma volume, or red cell volume. The immediate post-race serum sodium concentration was significantly lower (p = 0.004) in the cramp group (mean (SD), 139.8 (3.1) mmol/l) than in the control group (142.3 (2.1) mmol/l). The immediate post-race serum magnesium concentration was significantly higher (p = 0.03) in the cramp group (0.73 (0.06) mmol/l) than in the control group (0.67 (0.08) mmol/l). CONCLUSIONS: There are no clinically significant alterations in serum electrolyte concentrations and there is no alteration in hydration status in runners with EAMC participating in an ultra-distance race.

Adult↗
PubMed2004

Weight changes, medical complications, and performance during an Ironman triathlon.

BACKGROUND: Subjects exercising without fluid ingestion in desert heat terminated exercise when the total loss in body weight exceeded 7%. It is not known if athletes competing in cooler conditions with free access to fluid terminate exercise at similar levels of weight loss. OBJECTIVES: To determine any associations between percentage weight losses during a 224 km Ironman triathlon, serum sodium concentrations and rectal temperatures after the race, and prevalence of medical diagnoses. METHODS: Athletes competing in the 2000 and 2001 South African Ironman triathlon were weighed on the day of registration and again immediately before and immediately after the race. Blood pressure and serum sodium concentrations were measured at registration and immediately after the race. Rectal temperatures were also measured after the race, at which time all athletes were medically examined. Athletes were assigned to one of three groups according to percentage weight loss during the race. RESULTS: Body weight was significantly (p<0.0001) reduced after the race in all three groups. Serum sodium concentrations were significantly (p<0.001) higher in athletes with the greatest percentage weight loss. Rectal temperatures were the same in all groups, with only a weak inverse association between temperature and percentage weight loss. There were no significant differences in diagnostic indices of high weight loss or incidence of medical diagnoses between groups. CONCLUSIONS: Large changes in body weight during a triathlon were not associated with a greater prevalence of medical complications or higher rectal temperatures but were associated with higher serum sodium concentrations.

Blood Pressure↗
PubMed2004

Logical limitations to the "catastrophe" models of fatigue during exercise in humans.

A central debate in the exercise sciences is the cause of the fatigue that develops especially during high intensity exercise of short duration. The most popular theory holds that this form of exercise is limited by a peripherally based, metabolite induced failure of skeletal muscle contractile function, independent of reduced muscle activation by the central nervous system; so-called peripheral fatigue. This theory arose originally from studies undertaken by Nobel Laureate Sir Archibald Vivian Hill and colleagues in Manchester, UK in the 1920s. In turn, their interpretations were crucially influenced by the earlier 1907 findings of Sir Frederick Gowland Hopkins, Nobel Laureate for his discovery of the vitamins, and Walter Morley Fletcher. The original model of Hill and his colleagues proposed that performance during exercise of high intensity was limited by skeletal muscle anaerobiosis that developed as the result of a limiting skeletal muscle blood flow, following the onset of myocardial ischaemia. Such skeletal muscle anaerobiosis ultimately prevented the neutralization of the lactic acid that, Hill believed, initiated muscle contraction. The resulting lactic acid accumulation impaired skeletal muscle relaxation, causing the (involuntary) termination of exercise. The evolutionary progression of this model led to the "catastrophe theory" of Richard Edwards, which posits that exercise terminates when the physiological and biochemical limits of the body are exceeded, causing a catastrophic failure of intracellular homeostasis. This paper addresses six hallmark physiological requirements that must be correct if Hill's cardiovascular/ anaerobic/catastrophic model is the exclusive explanation for the fatigue that develops during maximum exercise to exhaustion. This leads to a review of the evidence supporting other, related "catastrophe" models that have been developed to explain fatigue during exercise of lower intensities and longer durations. It is concluded that there is little published evidence supporting the theory that fatigue occurs only after physiological homeostasis fails according to the prediction of these catastrophe models. Rather, it is proposed that fatigue in any form of exercise may form part of a regulated, anticipatory response co-ordinated in the subconscious brain. The ultimate goal of this regulation is to preserve homeostasis in all physiological systems during exercise, regardless of intensity or duration or the environmental conditions in which it is undertaken.

Energy Metabolism↗
PubMed2004

Evidence for complex system integration and dynamic neural regulation of skeletal muscle recruitment during exercise in humans.

A model is proposed in which the development of physical exhaustion is a relative rather than an absolute event and the sensation of fatigue is the sensory representation of the underlying neural integrative processes. Furthermore, activity is controlled as part of a pacing strategy involving active neural calculations in a "governor" region of the brain, which integrates internal sensory signals and information from the environment to produce a homoeostatically acceptable exercise intensity. The end point of the exercise bout is the controlling variable. This is an example of a complex, non-linear, dynamic system in which physiological systems interact to regulate activity before, during, and after the exercise bout.

Exercise↗
PubMed2004

From catastrophe to complexity: a novel model of integrative central neural regulation of effort and fatigue during exercise in humans.

It is a popular belief that exercise performance is limited by metabolic changes in the exercising muscles, so called peripheral fatigue. Exercise terminates when there is a catastrophic failure of homoeostasis in the exercising muscles. A revolutionary theory is presented that proposes that exercise performance is regulated by the central nervous system specifically to ensure that catastrophic physiological failure does not occur during normal exercise in humans.

Central Nervous System↗
PubMed2003

Low frequency of the "plateau phenomenon" during maximal exercise in elite British athletes.

A plateau in oxygen consumption (VO(2)) has long been considered the criterion for maximal effort during an incremental exercise test. But, surprisingly, the termination of a maximum exercise test often occurs in the absence of a VO(2) plateau. To explain this inconsistency, some have proposed that an oxygen limitation in skeletal muscle occurs only in elite athletes. To evaluate this hypothesis, we determined the frequency with which the "plateau phenomenon" developed in a group of elite male and female athletes. Fifty subjects performed a continuous incremental treadmill test to measure maximal oxygen consumption (VO(2max)). Treadmill velocity increased by 0.31 m s(-1) until the respiratory exchange ratio ( R) reached 1.00. Thereafter the treadmill gradient increased by 1% each minute until exhaustion. The VO(2max) was the highest VO(2) sustained for 60 s. Three criteria were used to determine maximal efforts: (1) a plateau in the VO(2), defined as an increase of less than 1.5 ml kg(-1) min(-1); (2) a final R of 1.1 or above; (3) a final heart rate (HR) above 95% of the age-related maximum. Mean VO(2max) exceeded 65 ml kg(-1) min(-1) in both groups. The criteria for R and HR were satisfied by 72% of males and 56% females, and 55% of males and 69% of females, respectively. In contrast a VO(2) plateau was identified in only 39% of males and 25% of females. These findings refute the twin arguments: (1) that the absence of a "plateau phenomenon" results from an inadequate motivational effort in poorly trained athletes and (2) that the "plateau phenomenon" and a consequent skeletal muscle anaerobiosis occur only in athletes with the highest VO(2max) values.

Adult↗
PubMed2003

EMG amplitude in maximal and submaximal exercise is dependent on signal capture rate.

This study analysed the effect of different electromyographic (EMG) capture rates during maximal voluntary contraction, submaximal and maximal dynamic cycling activity on EMG amplitude and signal characteristics. Ten healthy subjects participated in this study. Peak power output (PPO) and maximal isometric force output (MVC) were measured, followed by a progressive cycle ride on a cycle ergometer. Electromyographic (EMG) data were simultaneously captured during the MVC and cycling activities at frequencies of 32, 64, 128, 256, 512, 1024 and 1984 Hz. Significant differences in amplitude were found (p < 0.01) between MVC, submaximal (SUB) and maximal cycling activities (PWATT) for all capture rates. Asymptote values for IEMG amplitude occurred at EMG capture rates of 1604 +/- 235.6 Hz during MVC, 503.1 +/- 236.2 Hz during PWATT and 326.2 +/- 105.4 Hz during SUB cycling activity and were significantly different (p < 0.01). No significant differences were found for force/EMG ratios between PWATT and MVC at 1984 Hz capture rates (3.8 +/- 1.7 N/V vs 2.5 +/- 0.9 N/V) while significant differences occurred at 32 Hz capture rate (6.2 +/- 3.8 vs 16.0 +/- 8.0; p < 0.01). Low correlations were found between EMG activity captured at 1984 Hz during PWATT and lean thigh volume (r = 0.36) and MVC (r = 0.32). Asymptote values found on this study suggest that data captured below 326 Hz for SUB, 503 Hz for PWATT and 1604 Hz for MVC are not reliable. Therefore apparatus capturing EMG data at low frequencies from these values cannot be used for quantitative data analyses.

Adult↗
PubMed2003

Effects of supramaximal exercise on the electromyographic signal.

AIM: To determine the neuromuscular recruitment characteristics during supramaximal exercise. METHODS: Ten healthy subjects completed the Wingate anaerobic test (WAT) cycling protocol. Electromyographic (EMG) data and rate of fatigue were recorded throughout the cycling. RESULTS: The mean (SD) rate of fatigue (decrease in power output) was 44.5 (8.6)%. No significant change was found in EMG amplitude. A significant decrease (p<0.01) in mean power frequency spectrum was found over the 30 second period. CONCLUSIONS: During WAT, mean power frequency spectrum was attenuated with no decline in EMG amplitude, which may be caused by an accumulation of metabolites in the periphery. However, it is also possible that the feedback loop from intramuscular metabolism to the central nervous system is unable, within the 30 second period of the WAT, to affect neural recruitment strategy.

Adult↗
PubMed2002

The effects of heat stress on neuromuscular activity during endurance exercise.

This study analysed the effect of hot (35 degrees C) and cold (15 degrees C) environments on electromyographic (EMG) signal characteristics, skin and rectal temperatures and heart rate during progressive endurance exercise. Eight healthy subjects performed three successive 15-min rides at 30%, 50% and 70% of their peak sustained power output and then cycled at increasing (15 W/min) work rates to exhaustion in both 35 degrees C and 15 degrees C environments. Skin and rectal temperatures, heart rate and EMG data were measured during the trials. The skin temperatures were higher and the subjects felt more uncomfortable in the hot conditions (Bedford scale) ( P<0.01). Rectal temperature was slightly, but not significantly, higher under hot conditions. Heart rate was significantly higher in the hot group (between condition P<0.05). Peak power output (267.4+/-67.7 W vs. 250.1+/-61.5 W) and time-to-exhaustion (55.7+/-16.7 min vs. 54.5+/-17.1 min) (COLD vs. HOT) were not different between conditions. There were no differences in integrated EMG (IEMG) or mean power frequency spectrum between conditions. Rating of perceived exertion increased similarly in both conditions over time. Although the hot conditions increased heart rate and skin temperature, there were no differences in muscle recruitment or maximal performance, which suggests that the thermal stress of 35 degrees C, in combination with exercise, did not impair maximal performance in this study.

Adult↗
PubMed2002

Effects of a novel bicycle saddle on symptoms and comfort in cyclists.

BACKGROUND: While the bicycle frame and other parts of the bicycle have undergone many improvements, the bicycle saddle has remained relatively unchanged since it was first designed more than 100 years ago. Given the number and range of cycling injuries believed to result from the saddle, this is surprising. This study investigated the effects of a novel bicycle saddle on saddle-related comfort and symptoms during cycling. METHOD: Eleven competitive or recreational cyclists, 6 females and 5 males, performed three 2-hour stationary cycle rides in the laboratory, using their personal bicycles. Ride 1 was performed using the standard bicycle saddle and rides 2 and 3 using the novel bicycle saddle. Subjects reported saddle comfort rating scores (SC) while using the different saddles. Subjects also completed a questionnaire evaluating saddle symptoms (SS) when using either the conventional or the novel bicycle saddle during daily cycling. RESULTS: The most common saddle-related medical complaint with chronic use of the conventional saddle was painful pubic bones, with or without chaffing. Others were severe chaffing, saddle sores, chaffing and back pain, and painful pubic bones associated with a loss of feeling in the pelvic area. The mean SS rating score during the 2-hour laboratory ride was significantly less for the novel saddle (11.6 +/- 1.2 versus 19.1 +/- 3.2 arbitrary units, P < 0.01). Similarly the mean SC score was significantly lower for the novel saddle (36.2 +/- 10.5 v. 54.7 +/- 11.2 arbitrary units). Values for both SC scores were similar for rides 2 and 3. On completion of the trial all subjects indicated that they would continue to use the novel saddle in preference to the conventional saddle. Three months later 9 subjects (82%) reported continued use of this saddle in preference to the conventional saddle. CONCLUSION: These results show conclusively that this novel bicycle saddle: (i) significantly reduced reported symptoms during daily cycling compared with the conventionally designed cycling saddle; (ii) significantly improved saddle comfort during 2-hour cycles in the laboratory, such that (iii) when given the option the majority (82%) of the subjects chose to use this saddle 3 months later. Furthermore, the beneficial effects of the novel saddle were apparent during its first use, suggesting that the novel saddle is effective because the design is anatomically correct.

Adult↗