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Biomedical subjects

M Rayson

Publications and source records attributed to M Rayson.

5 recordsLinked to original sources
PubMed2003

Ambient temperature and the pituitary hormone responses to exercise in humans.

Pituitary hormones have an important role during exercise yet relatively little is known about the stimulus for their release. Body temperature progressively increases during prolonged steady-state exercise in the heat and we have investigated the role that this may play in the release of prolactin, growth hormone and cortisol (as an indicator of adrenocorticotropic hormone) into the circulation. Fit young male subjects exercised at 73% V(O2,max) until volitional fatigue at 20 degrees C and at 35 degrees C (30% relative humidity at both temperatures). Rectal temperature and mean skin temperature were monitored and blood samples analysed for lactate, glucose, cortisol, growth hormone and prolactin concentrations. During the first 20 min, core temperature rose continuously and to a similar extent at both temperatures, while mean skin temperature was approximately 4 degrees C lower during exercise in the cool. Blood glucose concentration was essentially constant throughout the period of exercise while lactate concentration increased in the first 10 min and then remained constant with very similar changes in the two exercise conditions. Prolactin and growth hormone concentrations both increased during the exercise period while the concentration of cortisol declined slightly before rising slightly over the 40 min period. Prolactin release was significantly greater when exercise was carried out in the heat while there was no difference in the release of growth hormone or cortisol in the two conditions. When plotted as a function of rectal temperature, growth hormone concentration showed a linear relationship which was the same at ambient temperatures of 35 degrees C and 20 degrees C. Prolactin concentration had a curvilinear relationship with rectal temperature and this differed markedly at the two ambient temperatures. Cortisol concentration showed no dependence on any measure of body temperature. Our results are consistent with some aspect of body temperature being a stimulus for growth hormone and prolactin secretion; however, the precise mechanism clearly differs between the two hormones and we suggest that skin temperature modulates prolactin release, but does not affect the release of growth hormone.

Adaptation, Physiological↗
PubMed2000

Development of physical selection procedures for the British Army. Phase 2: relationship between physical performance tests and criterion tasks.

This paper is the second in a series of three to describe the development of physical selection standards for the British Army. The first paper defined criterion tasks (single lift, carry, repetitive lift and carry, and loaded march tasks) and set standards on the criterion tasks for all British Army trades. The principal objective was to determine which combination of physical performance tests could be best used to predict criterion task performance. Secondary objectives included developing so-called 'gender-free' and 'gender-unbiased' models. The objectives were met by analysing performance data on the criterion tasks and a large battery of physical performance tests collected from 379 trained soldiers (mean age 23.5 (SD 4.45) years, stature 1734 (SD 79.5) mm, body mass 71.4 (SD 10.58) kg). Objective 1 was met: the most predictive physical performance tests were identified for all criterion tasks. Both single lift tasks were successfully modelled using muscle strength and fat free mass scores. The carry model incorporated muscle endurance and body size data, but the errors of prediction were large. The repetitive lift models included measures of muscle strength and endurance, and body size, but errors of prediction were also large. The loaded march tasks were successfully modelled incorporating indices of aerobic fitness, supplemented by measures of strength, endurance or body size and composition. The secondary objectives were partially fulfilled, though limitations in the data hampered the process. Although only one model (a loaded march) was gender-free, three models were gender-related (i.e. contained 'gender' explicitly in the model). The remaining six were gender-specific (i.e. were appropriate for men or for women). Owing to both a lower accuracy of prediction in women's scores and a greater tendency for the women's scores to be distributed around the pass standards, a greater percentage of women than men were misclassified as passing or failing, resulting in indirect discrimination. A validation of the models in a separate sample of the user population of recruits is reported in the third paper in this series.

Adult↗
PubMed1999

Angiotensin-converting-enzyme gene insertion/deletion polymorphism and response to physical training.

BACKGROUND: The function of local renin-angiotensin systems in skeletal muscle and adipose tissue remains largely unknown. A polymorphism of the human angiotensin converting enzyme (ACE) gene has been identified in which the insertion (I) rather than deletion (D) allele is associated with lower ACE activity in body tissues and increased response to some aspects of physical training. We studied the association between the ACE gene insertion or deletion polymorphism and changes in body composition related to an intensive exercise programme, to investigate the metabolic effects of local human renin-angiotensin systems. METHODS: We used three independent methods (bioimpedance, multiple skinfold-thickness assessment of whole-body composition, magnetic resonance imaging of the mid-thigh) to study changes in body composition in young male army recruits over 10 weeks of intensive physical training. FINDINGS: Participants with the II genotype had a greater anabolic response than those with one or more D alleles for fat mass (0.55 vs -0.20 kg, p=0.04 by bioimpedance) and non-fat mass (1.31 vs -0.15 kg, p=0.01 by bioimpedance). Changes in body morphology with training measured by the other methods were also dependent on genotype. INTERPRETATION: II genotype, as a marker of low ACE activity in body tissues, may conserve a positive energy balance during rigorous training, which suggests enhanced metabolic efficiency. This finding may explain some of the survival and functional benefits of therapy with ACE inhibitors.

Adipose Tissue↗
PubMedDate not supplied

Modelling the associations of BMI physical activity and diet with arterial blood pressure: some results from the Allied Dunbar National Fitness Survey.

In order to identify risk factors (e.g. physical inactivity, dietary composition) associated with blood pressure within a given population, it is necessary to adjust for differences in known associations (e.g. age, body weight) using a method such as the analysis of covariance. However, the blood pressure results from the Allied Dunbar National Fitness Survey (ADNFS) were found to be non-linear with age, positively skewed (with heteroscedastic errors) and therefore non-normally distributed. Hence, before valid inferences can be drawn from such data, there is a clear need to formulate an appropriate model for blood pressure that will overcome these undesirable characteristics. A multiplicative model (with allometric body size components) was proposed and fitted to the ADNFS blood pressure results. After a logarithmic transformation the parsimonious solution was able to confirm the association with BMI, the non-linear changes with age, and overcome the heteroscedastic and positively skewed errors, i.e. the residuals from the fitted log-linear models for both systolic and diastolic blood pressure were symmetric and normally distributed. Other factors were found to make a significant additional contribution to the prediction of blood pressure. Cyclists, participants in vigorous physical activity and those subjects who consumed more fresh fruit, rice or pasta, and wine were found to have significantly lower mean levels of blood pressure. Indeed, the gap in blood pressure between participants and non-participants in vigorous physical activity increased further with age. However, subjects who drank more beer tended to have significantly higher mean levels of blood pressure. Thus by developing an appropriate model for arterial blood pressure, some well known, and some less well known, associations with arterial blood pressure have been identified. The results suggest that physical activity and other lifestyle factors may protect against hypertension.

Adipose Tissue↗