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PubMed1995

Establishing percentiles for junior tennis players based on physical fitness testing results.

An important aspect of this study was the establishment of a data base. A broad data base allows for data on certain parameters to be greatly expanded and will also enhance the use and interpretation of statistical methods. A longitudinal study of these variables may also assist in monitoring the players' progress over a period of time, and can provide a useful supplement to subjective coaching appraisals. The means and standard deviation for each test were calculated according to the USTA age and gender groups, that is, 12s, 14s, and 16s for each separate gender. Additionally, the mean and standard deviations for the ages, heights, and weights of each grouping were also calculated. Once the means and standard deviations were calculated, percentile tables were developed for each of the USTA groupings (by age and gender). The percentiles for each USTA test are presented in Appendix 1. A percentile is defined as the point on the distribution below which a given percentage of the scores is found. Percentiles can provide a norm-referenced interpretation of an individual score within a distribution that often consists of scores from a comparable group of individuals. Using the USTA protocol, players and coaches now have a set of normative data by which individual player's fitness scores may be compared with participants of the USTA Area Training Centers (See appendix 1). From the test results, coaches and players can determine which fitness areas need to be improved for athletes on an individual basis. Specific training programs can then be designed based on an athlete's fitness testing results. Proper interpretation of the USTA fitness testing data base results can lead to an easy way to determine the relative position of a given fitness score in the distribution, recognizing weaker areas for the purpose of injury prevention and performance enhancement. Each player can be given a profile detailing their percentile rank relative to other area training center participants in their age group. Results of these fitness scores can prove to be of great assistance to coaches in designing proper training programs and may also give physicians some indication which weaknesses may potentially lead to injury. The sample player shown in Figure 1 and Table 2 is a right-handed female player ranked in the 12-years-old-and-under division. Her results clearly indicate very high scores in the agility and speed categories; however, her scores in the strength and power areas were significantly lower than other area training center participants in her age group.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1993

Physical and motor fitness level of Indian school-going boys.

A cross-sectional study of physical and motor fitness measurements was undertaken on 629 healthy Indian (Bengalee) school-going boys of 9-18 years. The study brought to light gradual increase in physical and motor fitness measurements with the advancement of age except physical fitness score. Major increments were recorded between 13 and 15 years of age. All the fitness test scores showed significant positive correlations with age, height and weight but Dash, Shuttle Run and PFI showed significantly negative relationship. Indian boys of the present study were superior in Sit and Reach and inferior in Vertical Jump to the Belgian boys of comparable ages. These boys showed higher values in Vertical Jump than American boys after the age of 13. Dash and Shuttle Run test scores of Indian boys fall between 15th to 25th and 30th to 45th percentiles of American Standard respectively. Besides, American boys are superior in Grip Strength to Indian boys. Percentile values of physical and motor fitness test scores of Indian (Bengalee) boys are, therefore, useful for determining their present fitness status and potentiality in that particular community for specific sports activity.

Adolescent↗
PubMed1993

Physical fitness and exercise training of individuals with mental retardation.

Recent social policies have focused on reentering persons with mental retardation (MR) into the work force and the mainstream of society. However, as individuals with MR age, their rate of institutionalization greatly outweighs that of the general population as well as children with MR. Health care organizations have expressed serious concern about the impact of an aging population with disabilities, particularly the cost associated with institutionalization. Considering that cardiovascular disorders are more common in population with than without MR, and that physical fitness has been directly related to work productivity among individuals with MR, physical fitness and exercise training have important implications for this population. Yet, available data suggest that individuals with MR have low levels of physical fitness, a higher incidence of obesity, and may respond differently to exercise training than persons without MR. This paper reviews current knowledge of physical fitness status, impact of exercise testing and training, and identifies differences between populations with and without MR, with special emphasis on trends associated with aging. This review is limited to three physical fitness components: obesity, cardiovascular fitness, and muscular strength and endurance, as these components have been shown to impact health and well-being, and are related to work performance of persons with MR. Suggestions for future research are also provided.

Aging↗
PubMed1996

Aerobic fitness testing: an update.

This study confirms that all three tests are reliable tools for the assessment of cardiorespiratory fitness and the prediction of aerobic capacity. While this particular study consisted of active, youthful subjects, subsequent studies at University College Chester have found similar findings with larger databases and a wider cross-section of subjects. The Astrand cycle test and Chester step test are submaximal tests with error margins of 5-15 per cent and therefore, not as precise as maximal testing. However, they still give a reasonably accurate reflection of an individual's fitness without the cost, time, effort and risk on the part of the subject. The bleep test is a low-cost maximal test designed for well-motivated, active individuals who are used to running to physical exhaustion. Used on other groups, results will not accurately reflect cardiorespiratory fitness values. While all three tests have inherent advantages and disadvantages, perhaps the most important factors are the knowledge and skills of the tester. Without a sound understanding of the physiological principles underlying these tests, and the ability to conduct an accurate assessment and evaluation of results in a knowledgeable and meaningful way, then the credibility of the tests and the results become suspect. However, used correctly, aerobic capacity tests can provide valuable baseline data about the fitness levels of individuals and data from which exercise programmes may be developed. The tests also enable fitness improvements to be monitored, help to motivate participants by establishing reasonable and achievable goals, assist in risk stratification and facilitate participants' education about the importance of physical fitness for work and for life. Since this study was completed, further tests have been repeated on 140 subjects of a wider age and ability range. This large database confirms the results found in this study.

Adult↗
PubMed1997

A comparison of goodness-of-fit tests for the logistic regression model.

Recent work has shown that there may be disadvantages in the use of the chi-square-like goodness-of-fit tests for the logistic regression model proposed by Hosmer and Lemeshow that use fixed groups of the estimated probabilities. A particular concern with these grouping strategies based on estimated probabilities, fitted values, is that groups may contain subjects with widely different values of the covariates. It is possible to demonstrate situations where one set of fixed groups shows the model fits while the test rejects fit using a different set of fixed groups. We compare the performance by simulation of these tests to tests based on smoothed residuals proposed by le Cessie and Van Houwelingen and Royston, a score test for an extended logistic regression model proposed by Stukel, the Pearson chi-square and the unweighted residual sum-of-squares. These simulations demonstrate that all but one of Royston's tests have the correct size. An examination of the performance of the tests when the correct model has a quadratic term but a model containing only the linear term has been fit shows that the Pearson chi-square, the unweighted sum-of-squares, the Hosmer-Lemeshow decile of risk, the smoothed residual sum-of-squares and Stukel's score test, have power exceeding 50 per cent to detect moderate departures from linearity when the sample size is 100 and have power over 90 per cent for these same alternatives for samples of size 500. All tests had no power when the correct model had an interaction between a dichotomous and continuous covariate but only the continuous covariate model was fit. Power to detect an incorrectly specified link was poor for samples of size 100. For samples of size 500 Stukel's score test had the best power but it only exceeded 50 per cent to detect an asymmetric link function. The power of the unweighted sum-of-squares test to detect an incorrectly specified link function was slightly less than Stukel's score test. We illustrate the tests within the context of a model for factors associated with low birth weight.

Humans↗
PubMed1999

Goodness-of-fit for GEE: an example with mental health service utilization.

Suppose we use generalized estimating equations to estimate a marginal regression model for repeated binary observations. There are no established summary statistics available for assessing the adequacy of the fitted model. In this paper we propose a goodness-of-fit test statistic which has an approximate chi-squared distribution when we have specified the model correctly. The proposed statistic can be viewed as an extension of the Hosmer and Lemeshow goodness-of-fit statistic for ordinary logistic regression to marginal regression models for repeated binary responses. We illustrate the methods using data from a study of mental health service utilization by children. The repeated responses are a set of binary measures of service use. We fit a marginal logistic regression model to the data using generalized estimating equations, and we apply the proposed goodness-of-fit statistic to assess the adequacy of the fitted model.

Age Factors↗
PubMed2000

Rater agreement and the generalized Rudas-Clogg-Lindsay index of fit.

Rudas, Clogg and Lindsay proposed a new index of fit for contingency table analysis. Using the two-component mixture, where the first component with weight (1-w) represents the model to be tested and the second component with weight w is unstructured, the RCL index of lack of fit was defined to be the smallest mixing weight w(*) being compatible with the two-component mixture to be saturated. This index of fit, which is not sensitive to sample size, is applied to the problem of assessing agreement between two raters whereby three hypotheses (pure agreement, quasi-independence, independence) are considered. As quasi-independence comprises the two other hypotheses, a natural generalization of the RCL index of fit results from assuming the model itself to be composed of two submodels (pure agreement, independence) while the third component remains unstructured. Two examples demonstrate the application of this generalized RCL index of fit, with the first 3x3 contingency table having no empty cells, and the second 4x4 table having five of them. In both cases estimating the parameters and determining w(*) was possible without problems within the linear logistic framework for latent class analysis. A further analysis of the 4x4 table assumes the model to be the two-class latent class model that certainly does not belong to the family of standard models for contingency table analysis. Thus, in contrast to the recommendations given originally, the following conclusions seem to be justified: (i) the number of components representing the model may exceed one (generalized RCL index); (ii) the application of the original RCL index of fit may be extended to more complex models; and (iii) empty cells bear no problems so that this approach may be recommended in the case of both large and small sample sizes.

Dermatitis, Atopic↗
PubMed2007

Fitness and extra-group reproduction in male Verreaux's sifaka: An analysis of reproductive success from 1989-1999.

Adult males in social groups often compete with other male group members for access to adult females. In some primate species, males also seek mating opportunities in neighboring social groups. Such extra-group fertilizations (EGFs) provide an additional source of variation in male fitness. This additional component of fitness provided by EGFs must be incorporated into analyses that investigate sources of variation in male lifetime reproductive success. In this study, a model is analyzed in which male fitness over a 10-year sample period is decomposed into additive and multiplicative variance and covariance components. The data come from an ongoing study of a wild population of Verreaux's sifaka (Propithecus verreauxi verreauxi) located at Beza Mahafaly Special Reserve, Southwest Madagascar. Paternity and demographic data for 134 males are used to decompose male fitness into the following three multiplicative components: reproductive lifespan during sample period, fertility, and offspring survival. These multiplicative components are estimated for males reproducing within their resident groups plus (i.e., the additive portion) for males reproducing in neighboring social groups. The analysis shows that variation in fertility makes the largest contribution to variation in total fitness, followed by variation in amount of time spent in sample period (which is a proxy of total reproductive lifespan) and variation in offspring survival. EGFs contribute an important source of variation to male fitness, and numerous factors enhance the opportunities for EGFs in male sifaka. These include female choice, a high degree of home range overlap, and a limited mating season.

Animals↗
PubMed2002

Molecular dynamics simulation studies of induced fit and conformational capture in U1A-RNA binding: do molecular substates code for specificity?

Molecular dynamics (MD) simulations on stem loop 2 of U1 small nuclear RNA and a construct of the U1A protein were carried out to obtain predictions of the structures for the unbound forms in solution and to elucidate dynamical aspects of induced fit upon binding. A crystal structure of the complex between the U1A protein and stem loop 2 RNA and an NMR structure for the uncomplexed form of the U1A protein are available from Oubridge et al. (Nature, 1994, Vol. 372, pp. 432-438) and Avis et al. (Journal of Molecular Biology, 1996, Vol. 257, pp. 398-411), respectively. As a consequence, U1A-RNA binding is a particularly attractive case for investigations of induced fit in protein-nucleic acid complexation. When combined with the available structural data, the results from simulations indicate that structural adaptation of U1A protein and RNA define distinct mechanisms for induced fit. For the protein, the calculations indicate that induced fit upon binding involves a non-native thermodynamic substate in which the structure is preorganized for binding. In contrast, induced fit of the RNA involves a distortion of the native structure in solution to an unstable form. However, the RNA solution structures predicted from simulation show evidence that structures in which groups of bases are favorably oriented for binding the U1A protein are thermally accessible. These results, which quantify with computational modeling recent proposals on induced fit and conformational capture by Leuillot and Varani (Biochemistry, 2001, Vol. 40, pp. 7947-7956) and by Williamson (Nature Structural Biology, 2000, Vol. 7, pp. 834-837) suggest an important role for intrinsic molecular architecture and substates other than the native form in the specificity of protein-RNA interactions.

Computer Simulation↗
PubMed1990

A note on fitting one-compartment models: non-linear least squares versus linear least squares using transformed data.

Drug concentrations in one-compartment systems are frequently modeled using a single exponential function. Two methods of estimation are commonly used for determining the parameters of such a model. In the first method, non-linear least-squares regression is used to calculate the parameters. In the second method, the data are first transformed by a logarithmic function, and then the log-concentration data are fit using linear least-squares regression. The assumptions for fitting these models are discussed with special emphasis on which data points are most influential in determining parameter values. The similarities between fitting a linear regression model to the log-concentration data and fitting a weighted regression model to the original data are noted. An example is presented that illustrates the differences in fitting a model to the log-transformed data versus fitting unweighted and weighted models to the original-scale data.

Animals↗
PubMed1992

A comparison of cortical strain after cemented and press-fit proximal and distal femoral replacement.

Proximal and distal femoral replacements with intramedullary stems are usually cemented in place but frequently show severe bone remodeling changes in the long term, which can contribute to a loosening process. The remodeling is likely to be associated with stress and strain distribution. This study compared the strain patterns, particularly the maximum principal strains, between cemented and press-fit components in five cadaveric femurs by using a photoelastic coating technique. The specimens were loaded with 2,000 N in the sequences of intact femur and press-fit and cemented stems. On the medial side of the bone for proximal femoral replacements, the strain values for the press-fit stems on the proximal, middle, and distal regions were 73 +/- 11%, 78 +/- 15%, and 80 +/- 15% of normal, respectively, but for the cemented stems they were 53 +/- 15%, 57 +/- 19%, and 60 +/- 20%. The differences were statistically significant (p less than 0.05). On the lateral side, the overall strain values for the press-fit stem were higher than those for the cemented stem, but the differences were not statistically significant (p greater than 0.05). On the medial side of the distal femoral replacement, the strain values for the press-fit stems in the proximal and middle regions were significantly closer to normal than for the cemented stems. Because the press-fit femoral stems (both the proximal and distal replacement) transferred closer to normal strains than the cemented stems, less adverse bone remodeling may be expected, which could be reflected in increased longevity.

Analysis of Variance↗
PubMed1998

Versatile frequency domain fitting using time domain models and prior knowledge.

An iterative nonlinear least-squares fitting algorithm in the frequency domain using time domain models for quantification of complex frequency domain MR spectra is presented. The algorithm allows incorporation of prior knowledge and has both the advantage of time-domain fitting with respect to handling the problem of missing data points and truncated data sets and of frequency-domain fitting with respect to multiple frequency-selective fitting. The described algorithm can handle, in addition to Lorentzian and Gaussian lineshapes, Voigt and nonanalytic lineshapes. The program allows the user the design of his own fitting strategy to optimize the probability of reaching the global least-squares minimum. The application of the fitting program is illustrated with examples from in vivo 1H-, 31P-, and 13C-MR spectroscopy.

Algorithms↗
PubMedDate not supplied

The host environment drives HIV-1 fitness.

Viral fitness is defined by the ability of an individual genotype to produce infectious progeny in a specific environment. For HIV the environment is never constant but rather fluctuates in time and space. For instance, environmental factors that determine viral fitness during transmission from host to host are different to the pressures from either cytotoxic T-lymphocytes (CTLs) or antiviral drugs. Consequently, viral fitness is highly dependent on the environment and the accurate determination of this value therefore depends strongly on the chosen environmental setting. This review describes how the host environment imposes selective pressures on the virus that shape its genotype and fitness. The most important environments that the virus encounters throughout its life cycle and during natural infection are discussed. In order of appearance, CTLs are discussed, followed by neutralising antibodies and antiretroviral drug treatment. It then goes on to describe receptor molecules that mediate viral entry and intracellular restriction factors, which represent selective pressures that are present directly from the start of a natural infection. It concludes by discussing the complexity of viral fitness and how an accurate measure of viral fitness eventually may, for example, contribute to the improvement of antiretroviral therapy or help in the formulation of an optimal vaccination strategy.

Adaptation, Biological↗
PubMed2004

Goodness-of-fit tests for ordinal response regression models.

It is well documented that the commonly used Pearson chi-square and deviance statistics are not adequate for assessing goodness-of-fit in logistic regression models when continuous covariates are modelled. In recent years, several methods have been proposed which address this shortcoming in the binary logistic regression setting or assess model fit differently. However, these techniques have typically not been extended to the ordinal response setting and few techniques exist to assess model fit in that case. We present the modified Pearson chi-square and deviance tests that are appropriate for assessing goodness-of-fit in ordinal response models when both categorical and continuous covariates are present. The methods have good power to detect omitted interaction terms and reasonable power to detect failure of the proportional odds assumption or modelling the wrong functional form of a continuous covariate. These tests also provide immediate information as to where a model may not fit well. In addition, the methods are simple to understand and implement, and are non-specific. That is, they do not require prespecification of a type of lack-of-fit to detect.

Aortic Aneurysm, Abdominal↗
PubMed1994

Kinlsq: a program for fitting kinetics data with numerically integrated rate equations and its application to the analysis of slow, tight-binding inhibition data.

Kinlsq, a Matlab-based computer program for the least-squares fitting of parameters to kinetics data described by numerically integrated rate equations, is described, and three applications to the analysis of enzyme kinetics data are given. The first application was to the analysis of a simple bimolecular enzyme plus inhibitor binding curve. The kinlsq fit to these data was essentially identical to that obtained with the corresponding analytically integrated rate equation, validating kinlsq. The second application was to the fit of a numerically integrated Michaelis-Menten model to the progress curve for dipeptidyl peptidase IV-catalyzed hydrolysis of Ala-Pro-p-nitroanilide as a demonstration of the analysis of steady-state enzyme kinetics data. The results obtained with kinlsq were compared with the results obtained by fitting this time course with the integrated Michaelis-Menten equation, and with the results obtained by fitting the (S,dP/dt) transform of the data with the Michaelis-Menten equation. The third application was to the analysis of the inhibition of chymotrypsin by the slow, tight-binding inhibitor MeOSuc-Ala-Ala-Pro-boroPhe, data not readily amenable to other methods of analysis. These applications demonstrate how kinlsq can be used to fit rate constants, equilibrium constants, steady-state constants, and the stoichiometric relationships between components.

Amino Acid Sequence↗
PubMed1999

Work and Family Stress and Well-Being: An Examination of Person-Environment Fit in the Work and Family Domains.

Research indicates that work and family are significant sources of stress. However, this research has underemphasized the cognitive appraisal process by which work and family generate stress. This study used person-environment fit theory to examine how the comparison of work and family experiences to the person's values relates to stress and well-being. Using data from 1758 employees, we assessed fit regarding autonomy, relationships, security, and segmentation for both work and family, and examined the relationship of fit with work and family satisfaction, anxiety, depression, irritation, and somatic symptoms. In general, well-being improved as experiences increased toward values and improved to a lesser extent as experiences exceeded values. Well-being was also higher when experiences and values were both high than when both were low. These relationships were generally strongest for within-domain fit and well-being (i.e., work fit and work satisfaction, family fit and family satisfaction), and several relationships were moderated by work and family centrality. Copyright 1999 Academic Press.

Journal Article↗
PubMed1991

Variations in polymer fitness at elevated mutation rates.

Two series expressions were obtained that give the first and second order rates of change in population fitness during competitive replication at elevated mutation rates. At their zero-error limit, the respective power series reduces to the second (Fisher's theorem) and third moments of the fitness distribution. The first series maximized the variation in mean polymer fitness, for a given amount of population covariance. From experimental results reported by Spiegelman's group on evolution in vitro among Q beta RNA variants, it was demonstrated: (i) terms in the (second) series fall-off at a rate broadly equal to the replicase error (epsilon congruent to 10(-4); (ii) the rate of change in mean RNA fitness (polymer formation rate constant) corresponds to the variance in fitness; and (iii) agreement exists between second order rate changes in fitness and the third moment (skewness) regression line, extending over 20 successive replication reactions. The impact of these findings on the standard model of evolution has been discussed.

Biological Evolution↗
PubMedDate not supplied

Gamma variate fits to pharmacokinetic data.

The gamma variate, C = Ataexp(-bt), was tested, as a fitting function, with various real and error-free simulated intravascular and extravascular pharmacokinetic data sets and the results compared with polyexponential fits. For extravascular data, the gamma variate is only suitable to globally fit data which might otherwise be described biexponentially. For intravascular data, the gamma variate could only fit a limited range of the possible concentration-time profiles. Gamma variate fitting algorithms must minimize relative deviations; fits using unweighted sums of squared deviations gave excellent results at higher concentration values but consistently underestimated terminal descending portions of the data.

Analysis of Variance↗