Janet C. Rice

A continuous wave technique for the measurement of the elastic properties of cortical bone

A continuous wave technique is described for measuring the nine independent orthotropic elastic coefficients from a single cubic specimen. The side dimensions of this cubic specimen are on the order of 5 mm. Because of the small size of the specimen, the spatial resolution of material inhomogeneity using this technique is quite good. Although it is possible to apply this technique to any elastic material such as woods or metals, the elastic properties of human and canine cortical femora are presented here. The orthotropic elastic coefficients and the variation of these coefficients are presented as a function of anatomical position.

On the dependence of the elasticity and strength of cancellous bone on apparent density.

This paper presents a statistical analysis of the pooled data from a number of previous experiments concerning the dependence of the Youngs moduli and strength of cancellous bone tissue upon apparent density. The results show that both the Youngs moduli and the strength are proportional to the square of apparent density of the tissue and are therefore proportional to one another. It is shown that the coefficient of proportionality is different for human and bovine tissue. It is concluded that the suggestion of Wolff (Das Gesetz der Transformation der Knochen, Hirschwald, Berlin, 1892) that compact bone tissue is simply more dense cancellous bone tissue is not an accurate statement when only the mechanical properties of these two tissues are considered. It is noted that estimates for the elastic modulus of the individual trabecula of human cancellous bone vary from 1 to 20 GPa and it is suggested that this question needs further study.

The fabric dependence of the orthotropic elastic constants of cancellous bone.

It has been proposed that the orthotropic elastic constants of cancellous bone depend upon a tensorial measure of anisotropy called fabric as well as the tissues structural density. Cowin (1985, Mechanics Mater, 4, 137-147; 1986, J. biomech. Engng 108, 83-88) developed explicit relationships for the elastic constant, structural density and fabric relationship. In this study the orthotropic elastic moduli, structural density, and fabric components were measured for 11 cancellous bone specimens from five bovine femora and for 75 specimens from three human proximal tibiae and fitted to these relationships using a least squares analysis. The relationships explained between 72 and 94% of the variance in the elastic constants. The relationships between the elastic constants and squared or cubed power functions of structural density had better predictive value over the entire distribution of the data than did expressions with linear functions of structural density.

The association between obesity and urban food environments.

Several studies have examined associations between the food retail environment and obesity, though virtually no work has been done in the urban South, where obesity rates are among the highest in the country. This study assessed associations between access to food retail outlets and obesity in New Orleans. Data on individual characteristics and body weight were collected by telephone interviews from a random sample of adults (N = 3,925) living in New Orleans in 2004–2005. The neighborhood of each individual was geo-mapped by creating a 2-km buffer around the center point of the census tract in which they lived. Food retailer counts were created by summing the total number of each food store type and fast food establishment within this 2-km neighborhood. Hierarchical linear models assessed associations between access to food retailers and obesity status. After adjusting for individual characteristics, each additional supermarket in a respondent’s neighborhood was associated with a reduced odds for obesity (OR 0.93, 95% CI 0.88–0.99). Fast food restaurant (OR 1.01, 95% CI 1.00–1.02) and convenience store (OR 1.01, 95% CI 1.00–1.02) access were each predictive of greater obesity odds. An individual’s access to food stores and fast food restaurants may play a part in determining weight status. Future studies with longitudinal and experimental designs are needed to test whether modifications in the food environment may assist in the prevention of obesity.

Neighborhood food environments and Body Mass Index: the importance of in-store contents.

BACKGROUND Most public health studies on the neighborhood food environment have focused on types of stores and their geographic placement, yet marketing research has long documented the influence of in-store shelf-space on consumer behavior. PURPOSE This paper combines these two strands of research to test whether the aggregate availability of specific foods in a neighborhood is associated with the BMIs of its residents. METHODS Fielded from October 2004 to August 2005, this study combines mapping of retail food outlets, in-store surveys, and telephone interviews of residents from 103 randomly sampled urban census tracts in southeastern Louisiana. Linear shelf-space of fruits, vegetables, and energy-dense snack foods was measured in 307 food stores in the study tracts. Residential addresses, demographic information, and heights and weights were obtained from 1243 respondents through telephone interviews. Cumulative shelf-space of foods within defined distances of each respondent was calculated using observations from the in-store survey and probability-based assignments of shelf-space to all unobserved stores in the area. RESULTS After controlling for sociodemographic variables, income, and car ownership, regression analysis, conducted in 2008, showed that cumulative shelf-space availability of energy-dense snack foods was positively, although modestly, associated with BMI. A 100-meter increase in shelf-space of these foods within 1 kilometer of a respondents household was associated with an additional 0.1 BMI points. Fruit and vegetable shelf-space was not significantly related to BMI. CONCLUSIONS Interventions that seek to improve the neighborhood food environment may need to focus on more than just increasing access to healthy foods, because the results suggest that the availability of energy-dense snack foods plays a role in weight status.

Oral contraceptives use and the risk of myocardial infarction: a meta-analysis

This meta-analysis of oral contraceptive use in relation to myocardial infarction is based on 19 case-control studies and 4 cohort studies that met pre-stated inclusion criteria. A comprehensive literature search was performed using the MEDLINE computerized database (for studies from January 1966 through October 2002). In addition, a manual search was performed for references cited in published original and reviewed articles. Current oral contraceptive (OC) users have an overall adjusted odds ratio (OR) of myocardial infarction (MI) of 2.48 [95% confidence interval (CI): 1.91-3.22] compared to never-users. The risk of MI for past OC users is not significantly different from that for never-users, overall OR = 1.15 (95% CI: 0.98-1.35; p = 0.096).

Implementation of condom social marketing in Louisiana, 1993 to 1996.

OBJECTIVES This article describes the implementation and impact of the first statewide condom social marketing intervention in the United States. METHODS A statewide social marketing program made condoms freely available in 93 public health clinics, 39 community mental health centers, 29 substance abuse treatment sites, and more than 1000 businesses in neighborhoods with high rates of sexually transmitted diseases (STDs) and HIV. Surveys about condom use were conducted annually. RESULTS Between 1994 and 1996, more than 33 million condoms were distributed without significant opposition. Over time, self-reported condom use at the last sexual encounter increased among African American women (from 28% in 1994 to 36% in 1996), particularly African American women with 2 or more sex partners (from 30% to 48%). Condom use at the last sexual encounter increased among African American men (from 40% in 1994 to an average of 54% in 1996). The number of reported sex partners did not increase. CONCLUSIONS Condom social marketing can be successfully implemented in the United States. The widespread availability of free condoms is associated with increased condom use, particularly among persons at high risk for STDs and HIV.

School-Level Intraclass Correlation for Physical Activity in Adolescent Girls

PURPOSE The Trial for Activity in Adolescent Girls (TAAG) is a multi-center group-randomized trial to reduce the usual decline in moderate to vigorous physical activity (MVPA) among middle-school girls. In group-randomized trials, the group-level intraclass correlation (ICC) has a strong inverse relationship to power and a good estimate of ICC is needed to determine sample size. As a result, we conducted a substudy to estimate the school-level ICC for intensity-weighted minutes of MVPA measured using an accelerometer. METHODS To estimate the ICC, each of six sites recruited two schools and randomly selected 45 eighth grade girls from each school; 80.7% participated. Each girl wore an Actigraph accelerometer for 7 d. Readings above 1500 counts per half minute were counted as MVPA. These counts were converted into metabolic equivalents (MET) and summed over 6 a.m. to midnight to provide MET-minutes per 18-h day of MVPA. Minutes of MVPA per 18-h day also were calculated ignoring the MET value. RESULTS The unadjusted school-level ICC for minutes of MVPA was 0.0205 (95%CI: -0.0079, 0.1727) and for MET-minutes of MVPA was 0.0045 (95% CI: -0.0147, 0.1145). Adjustment for age and BMI had no measurable effect, whereas adjustment for ethnicity reduced both ICC; adjusted values were 0.0175 (95% CI: -0.0092, 0.1622) for minutes of MVPA and 0.0000 (95% CI: -0.0166, 0.0968) for MET-minutes of MVPA. This information was used to calculate the number of schools and girls needed for TAAG to have 90% power to detect a 50% reduction in the decline of MET-minutes of MVPA between sixth and eighth grade. CONCLUSIONS The results called for 36 schools in TAAG, with 120 girls invited for measurements at each school, and a minimum participation rate of 80%.

The Ubiquity of Energy-Dense Snack Foods: A National Multicity Study

OBJECTIVES We assessed the availability and accessibility of energy-dense snacks in retail stores whose primary merchandise was not food and whether these varied by store type, region, or socioeconomic factors. METHODS We conducted systematic observations of 1082 retail stores in 19 US cities and determined the availability and accessibility of 6 categories of energy-dense snack foods. RESULTS Snack food was available in 41% of the stores; the most common forms were candy (33%), sweetened beverages (20%), and salty snacks (17%). These foods were often within arms reach of the cash register queue. We observed snack foods in 96% of pharmacies, 94% of gasoline stations, 22% of furniture stores, 16% of apparel stores, and 29% to 65% of other types of stores. Availability varied somewhat by region but not by the racial or socioeconomic characteristics of nearby census tracts. CONCLUSIONS Energy-dense snack foods and beverages, implicated as contributors to the obesity epidemic, are widely available in retail stores whose primary business is not food. The ubiquity of these products may contribute to excess energy consumption in the United States.

Development of a Direct Observation Instrument to Measure Environmental Characteristics of Parks for Physical Activity

BACKGROUND The studys purpose is to describe the development and evaluate the reliability (inter-observer agreement) and validity (rater agreement with a gold standard) of a direct observation instrument to assess park characteristics that may be related to physical activity. METHODS A direct observation instrument of 181 items was developed based on a conceptual model consisting of the following domains: features, condition, access, esthetics, and safety. Fifteen pairs of observers were trained and sent to two parks simultaneously to assess two Target Areas each. RESULTS Overall domain reliability was 86.9%, and overall geographic area reliability was 87.5%. Overall domain validity was 78.7% and overall geographic area validity was 81.5%. CONCLUSIONS Inter-rater reliability and validity were generally good, although validity was slightly lower than reliability. Objective items showed the highest reliability and validity. Items that are time-sensitive may need to be measured on multiple occasions, while items asking for subjective responses may require more supervised practice.