ISSN:0112-1642    

DOI:10.2165/00007256-198805010-00001

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

ISSN:0112-1642    

DOI:10.2165/00007256-198805010-00002

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryThe measurement of lean body and fat mass has developed with the increase in sports participation and the prescription of exercise. Quantification of body fat is also related to the treatment of obesity and to assess nutritional status. Different levels of evaluation have been proposed depending on expertise and need.Body density estimation from skinfold measurements has the advantage of simplicity, low cost and reasonable validity with predictions to within 3 to 4% for 70% of the population. The choice of prediction equation will depend on whether a generalised equation or a population-specific equation is appropriate. In all cases tester reliability and standard error of estimation should be established. There is strong evidence that a quadratic equation should be applied and that measures of the lower limb should be included with circumference and diameter measures to strengthen the prediction. Methodological errors need to be reduced by careful training of experimenters. Cross validation of regression equation will strengthen their validity, particularly when fat loss is to be quantified. The popularity of skin/old assessment of body fat is enhanced by the use of nomograms to predict body fat, although some accuracy will be lost. Skinfold estimation of body fat will continue to be a useful guide to adiposity for epidemiological studies and for popular usage.The hydrostatic weighing procedure to estimate body density is considered by many to be the criterion method. Under carefully controlled conditions with maximum subject compliance, it is highly reliable, particularly if residual volume can be determined accurately. The conversion of body density to percentage body fat is based on a number of assumptions which need to be considered with respect to the population being studied.Simple methods for adiposity include various weight for height indices, for example, the body mass index of weight (kg) + height2(m) which is often used to define obesity. frame size for the prediction of ideal weight and visual estimation for predicting body fat.Differences in the literature concerning fat cell size and number have their origins in variations of methodology. The choice of site for removal of tissue will influence the size of adipocytes, those obtained from deep sites are generally smaller than subcutaneous fat cells. If total cell number is determined from cell size, there will also be variability of cell number. The correlation between different methods of sizing cells is high for most techniques, but as the validity of the criterion method is not based on statistical evidence, the validity of the other methods cannot be readily accepted. When comparing the findings of different investigations, the methodology and type of analysis and sample site must be considered as they can exert a profound influence on the results. The controversy concerning changes in cell number and size during obesity will only be resolved when the limitations and differences in methodologies are fully resolved.Measuring fat from fat-soluble gases may be used concurrently with otherin vivoMeasurements, e.g. body water or body potassium, to establish average proportions and biological variability off at free mass components. With such information it would be possible to evaluate fundamental assumptions, and increase the usefulness of more widely applied techniques of body fat measurement. The procedure is prolonged and tedious for most subjects, and cannot easily be applied to large populations. Its potential is related to the direct measurement of fat, but it has not developed into a widely-used method.24-Hour urinary creatinine excretion is a widely used biochemical marker for body muscle mass estimation. After a creatine-controlled diet, the total 24-hour urine is analysed for creatinine content. However, no definite creatinine equivalence for human muscle has been established. An alternative approach for estimating muscle mass is to use plasma or serum creatinine values, although as yet these methods are not widely used.3-Methylhistidine is another excretory product which is proportional to human muscle mass. Excellent correlations have been found with total body potassium and fat-free body mass. The method is essentially similar to the measurement of 24-hour urinary creatinine. although it does require the use of an amino acid analyser and dietary control is essential.Total body water measurement can employ a range of dilution techniques. Deuterium oxide dilution is a common method and fulfils the methodological criteria.Total body potassium is a commonly used criterion method for evaluating lean body mass. It involves the measurement of the naturally occurring40K using screened scintillation detectors.Nuclear-based techniques are generally expensive, require a high level of operator training and are ethically questionable because of the use of radioactivity. The dosage is generally considered to be within an acceptable range and the specific information would be difficult to obtain by other techniques. The methods include neutron activation analysis. total body nitrogen, total body carbon, photon absorptiometry (single and dual), nuclear resonance scattering, and multiple isotope dilution. These methods are more likely to be restricted to direct clinical applications and will be used relatively rarely on healthy populations for body composition assessment.Ultrasound can be used to measure the depth of tissue interfaces, typically fat and muscle. Two types are commonly used, the B scan system to provide grey scale images. and the A scan device which records depth from reflected echoes. The latter method is reliable, portable, and could be of particular value in measurements on the obese.In body composition research computed tomography (CT) scanning, subject to the ethical considerations of radiography, is commonly used. A CT scanner produces a cross-sectional image of the distribution of x-ray attenuation. It can be used to validate existing anthropometric techniques and to provide an understanding of inter-relationships between metabolic activity and body composition. Disorders of fat distribution can be detected and may be significant in various clinical conditions. e.g. Cushing’s disease and diabetes. In prolonged weight reduction it may be useful to apply CT to establish the relative quantities of fat, muscle and bone. Similarly CT can detect the details of apparent weight increase with patients suffering from renal, cardiac or liver diseases which may have oedema masking muscle wastage. In sports medicine research the hypertrophy and atrophy of muscle after rehabilitation or immobilisation can be studied with precision by the CT method.Nuclear magnetic resonance imaging requires a large bore magnet capable of accepting the human body. The images, received by a radio frequency coil, are dependent on the behaviour of hydrogen nuclei in the magnetic field. The time taken for the protons to realign is detected and the image constructed similar to computed tomography. The realignment characteristics relate to specific tissues both in health and disease. Various modifications such as chemical shift imaging have improved the quality of the image such that it could now be usefully employed in body composition assessment. The capital cost of an NMR unit means that opportunities for use will be limited. However, the absence of radioactivity makes this approach ethically advantageous.The total body electrical conductivity method is a current induction approach in which the conductivity of the human body perturbs the electromagnetic.field such that fat and non-fat tissue can be evaluated. It appears to be both reliable and valid. Compared with total body water and total body potassium, total body electrical conductivity seemed to track short term changes in nitrogen balance more effectively. Its main disadvantage is that of capital cost, but it is safe, simple, convenient, rapid, non-invasive and requires low operator and recurrent expense. It undoubtedly distinguishes between fat and non-fat tissue. so may have considerable benefit in body composition measurement, particularly if a low-cost version can be produced. If this does nor occur, researchers are likely to pursue current injection techniques as a more,financially viable alternative.Electrical impedance or impedance plethysmography is a current injection method of relating body conductivity to composition. Typically a 50 kHz. 800μA electrical current is passed between the hand and foot and the resistance is recorded. This value is used in a regression equation to determine lean body mass, although the measurement is more directly related to total body water. The procedure is reliable, and has been shown to be valid in comparison with hydrostatic weighing. The quoted standard errors of estimate range from 1.7 to 6.1%, but population specific regression equations may improve this aspect. Its speed of use, safety and portability may make this approach particularly useful for epidemiological studies.Infrared interactance is a method of body composition based on the principles of light absorption, reflectance and near infrared spectroscopy. It developed from work on animal foodstuffs but has been used successfully on humans, although only to a limited extent.A true cross-validation using a distinct population is necessary as is the requirement for intra- and inter-reliability statistics on the methodology. Confounding results could occur because of inaccurate positioning of the fibre optic probe. The pressure of applying the probe could also influence the degree of energy scatter and absorption. The method uses 5 sites, so the precision of site location would, like skinfold readings, provide a potential source of error. However, the method has virtue in being rapid, safe and noninvasive so may, with further experimentation, prove to be a useful addition to body composition analytical techniques.

ISSN:0112-1642    

DOI:10.2165/00007256-198805010-00003

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryRecreational diving is a popular sport, although human ability to stay in and under water is severely limited physiologically. An understanding of these limitations enhances safety and enjoyment of sports diving.Breath-hold diving involves head-out water immersion, apnoea and submersion, exercise, cold stress, and pressure exposure. Each of these components, by itself, elicits prominent and specific physiological effects. Combination of these factors produces a unique and interesting physiological response generally known as diving reflex. Humans display weak diving responses, but exhibit no oxygen conservation function. Nevertheless, application of diving-induced physiological changes is now finding its way into clinical practice.Apnoea, face immersion, and head-out water immersion all show promise of clinical application. There are several spin-offs from diving research worth noting. Diuresis, enhancement of cardiac performance, and redistribution of blood flow, all produced by headout water immersion, have been shown to be clinically useful, besides providing physiological data useful to space travel. Results from investigations on apnoea have been shown to be relevant to the following: treating some forms of cardiac arrhythmias; understanding drowning, sudden infant death syndrome and sleep apnoea; and confirming hyperventilation as the major cause of drowning.In comparison to marine mammals, humans are poor divers because of severe physiological constraints which limit their breath-hold time, diving depth, and ability to conserve body heat. Although under special circumstances humans can achieve unusually long breath-hold time and reach exceptional depth with a single breath, the sustainable working time and depth are only about 1 minute and 5 metres, respectively. Hypothermia inevitably results in divers working in the ocean. Without thermal protection, the intolerable limit of 35°C is reached within 30 minutes in winter (10°C) water and within 60 to 90 minutes in summer. Nevertheless, effective harvest work can be performed by humans in the ocean, and recreational benefits enhanced when these physiological limitations are respected. An unusual circulatory state exists during head-out water immersion in that there is a sustained increase of stroke volume. This results in 30% increase in cardiac output when the subject is resting in thermal neutral water, indicating a substantial overperfusion for the oxygen requirement. Furthermore, animal experiments showed that the elevated blood flow is preferentially channeled to the liver, fat, and the organs in the splanchnic region. Moreover. head-out water immersion enhances the ability of kidney to eliminate excess body fluid.

ISSN:0112-1642    

DOI:10.2165/00007256-198805010-00004

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryMaximal oxygen intake (V̇O2 max) may be the most physiologically significant and, therefore, the most commonly measured parameter in the physiological assessment of well trained runners. To insure valid and reliable V̇O2 maxvalues, there are a number of practical concerns that must be addressed. An exercise modality must be selected that activates the specific muscle mass and duplicates the motion utilised in the runners’ training programme. Motorised treadmill running has been shown to allow the most efficient, valid and reproducible V̇O2 maxvalues in a controlled testing environment. A testing protocol must be used that is easily administered, comfortable for the runner, allows test completion within 10 minutes, uses grade increments at a constant speed, and is reproducible, Speeds should be selected that approximate the runner’s training pace. The criterion for the attainment of V̇O2 maxinclude the levelling off of V̇O2with an increase in work stage, the onset of extreme exhaustion, the respiratory exchange ratio exceeding 1.1, blood lactate levels approaching or exceeding 10 mmol/L, and ratings of perceived exertion of 19 or 20. Quality control in terms of standardisation of procedures and calibration and maintenance of equipment is essential for the minimisation of technological error. Measurement equipment must be affordable. dependable, easily calibrated, yield reproducible data, and be within the technical skill levels of the operating personnel.

ISSN:0112-1642    

DOI:10.2165/00007256-198805010-00005

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS