Biomedical subjects

Estelle V Lambert

Publications and source records attributed to Estelle V Lambert.

16 recordsLinked to original sources

PubMed2006

The rate of heat storage mediates an anticipatory reduction in exercise intensity during cycling at a fixed rating of perceived exertion.

The aim of the present study was to examine the regulation of exercise intensity in hot environments when exercise is performed at a predetermined, fixed subjective rating of perceived exertion (RPE). Eight cyclists performed cycling trials at 15 degrees C (COOL), 25 degrees C (NORM) and 35 degrees C (HOT) (65% humidity throughout), during which they were instructed to cycle at a Borg rating of perceived exertion (RPE) of 16, increasing or decreasing their power output in order to maintain this RPE. Power output declined linearly in all three trials and the rate of decline was significantly higher in HOT than in NORM and COOL (2.35 +/- 0.73 W min(-1), 1.63 +/- 0.70 and 1.61 +/- 0.80 W min(-1), respectively, P < 0.05). The rate of heat storage was significantly higher in HOT for the first 4 min of the trials only, as a result of increasing skin temperatures. Thereafter, no differences in heat storage were found between conditions. We conclude that the regulation of exercise intensity is controlled by an initial afferent feedback regarding the rate of heat storage, which is used to regulate exercise intensity and hence the rate of heat storage for the remainder of the anticipated exercise bout. This regulation maintains thermal homeostasis by reducing the exercise work rate and utilizing the subjective RPE specifically to ensure that excessive heat accumulation does not occur and cellular catastrophe is avoided.

Adaptation, Physiological↗

PubMed2006

Comparison of two methods of measuring physical activity in South African older adults.

The aim of this study was to assess the validity and reliability of the Yale Physical Activity Survey (YPAS) and the short version of the International Physical Activity Questionnaire (IPAQ) in older South African adults. The YPAS includes measures of weekly energy expenditure (EE) for housework, yard work, caregiving, exercise, and recreation. The IPAQ measures total time and EE during vigorous and moderate activity, walking, and sitting. The instruments were administered twice for test-retest reliability (men, n = 52, 68 +/- 5.4 years, and women, n = 70, 66 +/- 5.8 years). Data for criterion validity were obtained from accelerometers. YPAS reliability ranged from r = .44 to.80 for men and r = .59 to .99 for women (p < .0001). IPAQ reliability was lower for men (r = .29 to .76) than for women (r = .46 to .77). Criterion validity of the YPAS was .31 to .54 for men and .26 to .29 for women. The YPAS and short IPAQ had comparable results for reliability and criterion validity.

Aged↗

PubMed2006

The role of information processing between the brain and peripheral physiological systems in pacing and perception of effort.

This article examines how pacing strategies during exercise are controlled by information processing between the brain and peripheral physiological systems. It is suggested that, although several different pacing strategies can be used by athletes for events of different distance or duration, the underlying principle of how these different overall pacing strategies are controlled is similar. Perhaps the most important factor allowing the establishment of a pacing strategy is knowledge of the endpoint of a particular event. The brain centre controlling pace incorporates knowledge of the endpoint into an algorithm, together with memory of prior events of similar distance or duration, and knowledge of external (environmental) and internal (metabolic) conditions to set a particular optimal pacing strategy for a particular exercise bout. It is proposed that an internal clock, which appears to use scalar rather than absolute time scales, is used by the brain to generate knowledge of the duration or distance still to be covered, so that power output and metabolic rate can be altered appropriately throughout an event of a particular duration or distance. Although the initial pace is set at the beginning of an event in a feedforward manner, no event or internal physiological state will be identical to what has occurred previously. Therefore, continuous adjustments to the power output in the context of the overall pacing strategy occur throughout the exercise bout using feedback information from internal and external receptors. These continuous adjustments in power output require a specific length of time for afferent information to be assessed by the brain's pace control algorithm, and for efferent neural commands to be generated, and we suggest that it is this time lag that crates the fluctuations in power output that occur during an exercise bout. These non-monotonic changes in power output during exercise, associated with information processing between the brain and peripheral physiological systems, are crucial to maintain the overall pacing strategy chosen by the brain algorithm of each athlete at the start of the exercise bout.

Adaptation, Psychological↗

PubMed2006

Review of three tests of motor proficiency in children.

The present purpose is to provide clinicians, occupational and physical therapists, and educators with a comparative analysis of three tests of motor proficiency. The Bruininks-Oseretsky Test of Motor Proficiency, Movement Assessment Battery for Children, and Tufts Assessment of Motor Performance were developed to assess the motor skills of children with developmental delays. The selection criteria, interrater reliability, reproducibility, and recommended use of each test are reported here. Recommendations for use of each test include standardization of the sample population to ensure its appropriateness.

Adolescent↗

PubMed2005

Effects of elevated plasma adrenaline levels on substrate metabolism, effort perception and muscle activation during low-to-moderate intensity exercise.

The aim of this study was to differentiate the role of raised plasma adrenaline (Adr) concentrations from sympathoadrenal activation associated with moderate-intensity exercise, on muscle activation, cardiopulmonary responses, fuel metabolism, and ratings of perceived exertion (RPE) during low-intensity exercise. Two groups of subjects (MOD, n=6; LOW, n=7) cycled on two occasions for 90 min. MOD cycled at 68% VO(2max) with saline infusion, and at 34% VO(2max) with Adr infusion. LOW cycled twice at 34% VO(2max), with either Adr or saline infusion. Infusions (0.015 g Adr/kg/min) started at 15 min and increased plasma [Adr] somewhat higher than during exercise at 68% VO(2max) (approximately 1.9 vs. 1.4 nM, at 75 min). Mean plasma glucose and lactate concentrations during LOW were significantly higher with Adr than saline infusion (5.1+/-0.6 vs. 4.4+/-0.3 mmol/l, P<0.01 and 2.1+/-0.8 vs. 1.3+/-0.5 mmol/l, P<0.01, respectively). Elevated [Adr], without increased exercise intensity, did not alter glycogenolysis. There were also no effects of Adr infusion at 34% VO(2max) on heart rate, oxygen consumption, [FFA], respiratory exchange ratio, intramuscular triglyceride utilization, muscle activation or RPE. In conclusion, elevated [Adr] similar to those found during moderate-intensity exercise increased plasma glucose and lactate availability, but did not alter intramuscular fuel utilization, effort perception or muscle activation.

Adolescent↗

PubMed2005

Submaximal force production during perceptually guided isometric exercise.

The aim of this study was to examine submaximal isometric force production guided by perceptual feelings of exertion. Thirty young adults performed isometric knee extensions on an isokinetic dynamometer. Subjects performed five different tests; the first test was the same for all subjects (standard naïve test). During the standard naïve test, subjects were asked to randomly produce force at perceived contraction intensities (25%, 50% and 75% of their maximum voluntary contraction (MVC)), with 100% MVC performed as the final intensity. All intensities, including the 100% MVC, were randomly performed in the other four tests (control tests 1 and 2, post 20% MVC and post 100% MVC tests). Post 20% MVC and post 100% MVC tests included fatiguing isometric exercise at 20% and 100% MVC respectively, which were performed prior to the test protocol. Results show that absolute peak force increased with increasing intensity (P<0.001) during all tests. During the standard naïve test, absolute peak force at 25% and 50% MVC was significantly lower (P=0.009) compared to control test 2, post 20% MVC and 100% MVC tests, and relative peak force was lower at all intensities compared to all other tests (P<0.001). Absolute and relative peak force was most accurate at 50% MVC (-12.06 N and -2.42%, respectively). Prior fatiguing isometric exercise did not affect the subsequent perceptual response range. In conclusion, isometric force was most accurate at 25% MVC but under-produced (perceptually overestimated) during higher contraction intensities preceding a maximal voluntary contraction (100% MVC). The ability to match absolute force with target contraction intensities was most accurate at 50% MVC during all five experimental conditions and poor at opposite ends of the force domain. Furthermore, prior fatiguing isometric exercise did not have an effect on the subsequent perceptual response range.

Adult↗

PubMed2005

Development and validation of instruments measuring body image and body weight dissatisfaction in South African mothers and their daughters.

OBJECTIVE: We sought to validate questionnaires concerning body image perception, body size dissatisfaction and weight-related beliefs in multi-ethnic South African mothers and their daughters. SETTINGS AND SUBJECTS: Girls attending primary school (ages 9-12 years, n = 333) and their mothers (n = 204) were interviewed regarding their demographics and body image. Weight, height and skinfold thicknesses were measured. Body image questions and body mass index (BMI) were compared with silhouettes adapted from the Pathways Study for girls and Stunkard's body image figures for mothers. A Feel-Ideal Difference (FID) index score was created by subtracting the score of the silhouette selected by the participants as 'Ideal' from the one selected as most closely representing their current appearance or 'Feel'. We hypothesised that a higher FID index score would be associated with greater body size dissatisfaction. RESULTS: BMI percentiles in girls (r = 0.46, P < 0.05) and BMI in mothers (r = 0.68, P < 0.05) were positively correlated with the selected silhouettes based on size. Participants who reported feelings of being 'fat' and those who perceived that their family and friends were more dissatisfied with their body size had significantly higher FID index scores. Scores were lower in black than white girls (all P<0.05). No differences were found in FID index scores between ethnic groups of mothers. Internal reliability of the 'thin' and 'fat' belief constructs for girls was demonstrated by standardised Cronbach's alpha values > or = 0.7. CONCLUSION: Silhouettes, FID index, 'fat' and 'thin' belief constructs (in girls) are age-appropriate, culturally sensitive and can be used in further intervention studies to understand body image.

Adult↗

PubMed2005

The effects of medium-chain triacylglycerol and carbohydrate ingestion on ultra-endurance exercise performance.

The aims of the study were to determine if medium-chain triacylglycerol (MCT), ingested in combination with carbohydrate (CHO), would alter substrate metabolism and improve simulated competitive ultra-endurance cycling performance. Eight endurance-trained cyclists took part in this randomized, single-blind crossover study. On two separate occasions, subjects cycled for 270 min at 50% of peak power output, interspersed with four 75 kJ sprints at 60 min intervals, followed immediately by a 200 kJ time-trial. One hour prior to the exercise trials, subjects ingested either 75 g of CHO or 32 g of MCT, and then ingested 200 mL of a 10% CHO (wt/vol) solution or a 4.3% MCT + 10% CHO (wt/vol) solution every 20 min during the CHO and MCT trials, respectively. During the constant-load phases of the 270 min exercise trial, VO2. RER, and heart rate were measured at 30 min intervals and gastrointestinal (GI) symptoms were recorded. There was no difference in VO2 or RER between the MCT and CHO trials (P = 0.40). Hourly sprint (P = 0.03 for trial x time interaction) and time-trial times (14:30 +/- 0.58 vs. 12:36 +/- 1:6, respectively, P < 0.001) were slower in the MCT than the CHO trial. Half the subjects experienced GI symptoms with MCT ingestion. In conclusion, MCTs ingested prior to exercise and co-ingested with CHO during exercise did not alter substrate metabolism and significantly compromised sprint performance during prolonged ultra-endurance cycling exercise.

Adult↗

PubMed2005

Variability in exercise capacity and metabolic response during endurance exercise after a low carbohydrate diet.

The impact of altered blood glucose concentrations on exercise metabolism and performance after a low carbohydrate (CHO) diet was investigated. In random order, 1 wk apart, 9 trained men underwent euglycemic (CI) or placebo (PI) clamps, while performing up to 150 min of cycling at 70% VO2(max), after 48 h on a low CHO diet. The range in improvement in endurance capacity with glucose infusion was large (28 +/- 26%, P < 0.05). Fifty-six percent of subjects in CI failed to complete 150 min of exercise despite maintenance of euglycemia, while only 2 subjects in PI completed 150 min of exercise, despite being hypoglycemic. Total CHO oxidation remained similar between trials. Despite longer exercise times in CI, similar amounts of muscle glycogen were used to PI. Maintenance of euglycemia in the CHO-depleted state might have an ergogenic effect, however, the effect is highly variable between individuals and independent of changes in CHO oxidation.

Adult↗

PubMed2005

Effect of distance feedback on pacing strategy and perceived exertion during cycling.

PURPOSE: The aim of this study was to investigate whether providing incorrect distance feedback would alter pacing strategies, perceived exertion, and heart rate during 20-km cycling time trials (TT). METHODS: Well-trained cyclists (N=15) performed a peak power output (PPO) test, familiarization trial, and four 20-km cycling TT during which they were provided with only distance feedback using 1-km distance splits. For the control trial, subjects received accurate feedback at each kilometer split. In the increase trial, they received inaccurate feedback at 0.775 km for the first kilometer split with the distance increasing by 25 m each subsequent split up to 1.25 km in the final kilometer split. For the decrease trial, inaccurate feedback was provided at 1.25 km for the first kilometer split with the distance decreasing by 25 m each subsequent split up to 0.775 km in the final split. For the random trial, distance splits were randomized. RESULTS: No significant differences were found in the finishing times between trials. Pacing strategies were unaltered as suggested by similar power output profiles during all trials. RPE scores were also similar for all trials. However, average heart rate varied significantly between trials (P<0.05). CONCLUSIONS: These results suggest that exercise performance, pacing strategy, and RPE during a 20-km cycling TT are not altered by incorrect distance feedback. The data supported the existence of a pacing strategy that is set before exercise and that is unaffected by external distance feedback.

Adaptation, Physiological↗

PubMed2005

A novel energy expenditure prediction equation for intermittent physical activity.

PURPOSE: This study was designed to characterize the relative contributions of the current heart rate (HR) and HR in the previous minute to predict energy expenditure (EE) and to model these and other determinants to predict EE during intermittent activity. METHODS: Regularly exercising subjects (N=65, 36+/-9 yr, body mass index (BMI), 23.9+/- 2.5 kg.m) were tested. Body composition and maximal oxygen uptake (& OV0312;O2) were measured. On a separate day, subjects completed 12 x 4-min workloads, separated by 4 x 1-min rest periods, during which HR and & OV0312;O2 were continuously monitored. Using the intermittent activity calibration data, an EE model was developed. For validation, the final model was used to predict EE in a separate sample (N=17), who completed a gym training exercise session. Using the HR data, EE data were estimated using (a) the new model and were compared with (b) a previous model developed using a continuous incremental calibration test. RESULTS: The following variables contributed significantly to the estimation of EE during intermittent activity: age, gender, & OV0312;O2 max, current minute's HR, previous minute's HR, and an interaction variable consisting of previous minute's HR and & OV0312;O2 max. The final model yielded an R of 82% for the comparison of predicted and measured EE. When this model was applied to an independent sample for validation (N=17), improvements in EE prediction, when compared to the existing model (b), were most apparent during free-living non-continuous exercise. CONCLUSION: It is possible to improve the accuracy of predicting EE from HR, by incorporating both & OV0312;O2 max and the previous minute's HR in the prediction model.

Adult↗

PubMed2004

Deception and perceived exertion during high-intensity running bouts.

This investigation examined the overall and localized perceived exertion responses to repeated bouts of submaximal, high-intensity running when subjects were deceived. Well-trained male and female n = 40) runners were randomly assigned to four groups who completed three 1680-m bouts of running at 80-86% peak treadmill running speed. The two experimental groups, Expected Similar and Expected Increase, were deceived of the actual run intensities while the two control groups, Control Increase and Control Similar, were informed of the actual protocol. After each run, ratings of perceived exertion (RPE) were taken for the whole body, chest, legs, head, and other areas. No significant differences were found in overall RPE between deceived and control groups. However, there was a tendency for the Expected Increase group, deceived into believing the intensity would be higher than they were subsequently made to run, to experience an attenuated increase in RPE between runs compared to the control group (Control Increase) who were honestly informed. For all groups, legs and chest were given consistently higher localized exertion scores than the head and other areas. It appears that a precise system of afferent feedback mediates the overall perceived exertion response during high-intensity running, and psychological intervention that alters pre-exercise expectations has minimal feedforward effect on exertion ratings taken postexercise.

Adult↗

PubMed2004

The global cardiovascular diseases risk pattern in a peri-urban working-class community in South Africa. The Mamre study.

OBJECTIVES: To describe the cardiovascular disease (CVD) risk factors and the global burden of CVD risk in a peri-urban, working-class community of Mamre near Cape Town. To identify additional variables in the data set associated with the global CVD risk factor score. The latter was calculated using the major CVD risk factors in formulas derived from the Framingham global CVD risk calculations. Such variables could possibly be used for global CVD risk calculations, instead of depending on biochemical estimates for these calculations. METHODS: In a random population-based sample of 976 people aged 15 years and older, data on demography, smoking, physical activity, and alcohol use were collected. Blood pressure (BP), anthropometry, levels of serum glucose and lipids, and low-density lipoprotein cholesterol (LDL) particle sizes were also determined. These data allowed calculation of the global CVD risk profile with the Framingham study's formula. The data are age-standardized to the colored (mixed ancestry) population according to the 1996 South African census. RESULTS: The global CVD risk score suggested that men and women had a 5.2% and 4.2% probability, respectively, of having a CVD event in the next 10 years, while for those 55 years of age and older, the probability increased to more than 30% and 25%, respectively. Hypertension was found in 22% of men and 16% of women. Sixty-two percent of the men and 44% of the women smoked cigarettes, while 6% and 5% had diabetes, respectively. Hypercholesterolemia was present in 47% of men, and 46% of women. Small-dense LDL particles were present in 26% of men and 14% of women. A number of easily measured CVD risk factors could explain 40.3% of the variation of the global CVD risk score. These include aspects of the medical history provided by the patient, the inverse of the amount of physical activity and weight measurements, as well as height, and waist circumference. CONCLUSIONS: The people in Mamre have a high probability of suffering a CVD event in the next 10 years. Age and gender are the primary contributors to the global CVD risk score. The findings suggest the possibility of developing a global CVD risk score based on easily measured CVD risk factors for use in developing countries with limited resources.

Adolescent↗

PubMed2003

The role of dietary macronutrients in optimizing endurance performance.

We have evaluated the evidence underlying certain key nutritional recommendations for endurance sporting activities. A relatively high daily carbohydrate (CHO) intake (> 6 g/kg/d) and CHO ingestion (30-60 g/h) during exercise appears to delay the onset of fatigue. However, the mechanisms of this effect are governed in part by an attenuation of effort perception, rather than solely as a consequence of delaying an impending energy crisis. CHO loading and ingestion also impart some neuroprotection from fatigue during prolonged exercise, as well as high-intensity, intermittent exercise. In addition, the individual response to short-term (5- to 6-day) ingestion of a high-fat diet (> 60% of calories from fat) followed by 1-day CHO loading seems to vary widely, and is most likely to be of benefit only during ultra-endurance activities. Furthermore, CHO and protein intake in the postexercise period aid in protein synthesis and restoration of muscle glycogen stores. However, athletes and their advisors must be prepared to try various nutritional strategies in order to optimize both performance and training.

Diet↗

PubMed2002

Where does the black population of South Africa stand on the nutrition transition?

OBJECTIVE: To review data on selected risk factors related to the emergence of noncommunicable diseases (NCDs) in the black population of South Africa. METHODS: Data from existing literature on South African blacks were reviewed with an emphasis placed on changes in diet and the emergence of obesity and related NCDs. DESIGN: Review and analysis of secondary data over time relating to diet, physical activity and obesity and relevant to nutrition-related NCDs. SETTINGS: Urban, peri-urban and rural areas of South Africa. National prevalence data are also included. SUBJECTS: Black adults over the age of 15 years were examined. RESULTS: Shifts in dietary intake, to a less prudent pattern, are occurring with apparent increasing momentum, particularly among blacks, who constitute three-quarters of the population. Data have shown that among urban blacks, fat intakes have increased from 16.4% to 26.2% of total energy (a relative increase of 59.7%), while carbohydrate intakes have decreased from 69.3% to 61.7% of total energy (a relative decrease of 10.9%) in the past 50 years. Shifts towards the Western diet are apparent among rural African dwellers as well. The South African Demographic and Health Survey conducted in 1998 revealed that 31.8% of African women (over the age of 15 years) were obese (body mass index (BMI) > or = 30kg m(-2)) and that a further 26.7% were overweight (BMI > or = 25 to <30 kg m(-2)). The obesity prevalence among men of the same age was 6.0%, with 19.4% being overweight. The national prevalence of hypertension in blacks was 24.4%, using the cut-off point of 140/90 mmHg. There are limited data on the population's physical activity patterns. However, the effects of the HIV/AIDS epidemic will become increasingly important. CONCLUSIONS: The increasing emergence of NCDs in black South Africans, compounded by the HIV/AIDS pandemic, presents a complex picture for health workers and policy makers. Increasing emphasis needs to be placed on healthy lifestyles.

Adolescent↗

PubMedDate not supplied

The foetal origins of the metabolic syndrome--a South African perspective.

The developing world is experiencing a rise in the prevalence of obesity, diabetes and cardiovascular disease to such an extent that it is often described as an epidemic. The most common explanation advanced for this phenomenon is the so-called epidemiological transition, with the biological basis of the thrifty genotype. The thrifty genotype theory suggests that genes derived from times of deprivation may result in adaptations that have adverse effects in times of plenty. However, a divergent theory is the so-called foetal origins of chronic disease, which ascribes the epidemic, in part, to an adverse intrauterine environment. There is compelling evidence, based on large numbers of epidemiological studies conducted in both developing and developed countries, that small size at birth in full-term pregnancies is linked with the subsequent development of the major features of the metabolic syndrome, namely glucose intolerance, increased blood pressure, dyslipidaemia and increased mortality from cardiovascular disease.

Adult↗