Linguistic and Cognitive Profiles of 8- to 15-Year-Old Children With Specific Reading Comprehension Difficulties.

This article presents two studies investigating the role of executive functioning in written text comprehension in children and adolescents. In a first study, the involvement of executive functions in reading comprehension performance was examined in normally developing children in fifth grade. Two aspects of text comprehension were differentiated: literal and inferential processes. The results demonstrated that while three aspects of executive functioning (working memory, planning, and inhibition processes) were significantly predictive of the performance on the inferential questions of the comprehension test, these factors did not predict the scores on the literal tasks of the test. In a second experiment, the linguistic and cognitive profiles of children in third/fifth and seventh/ninth grades with a specific reading comprehension deficit were examined. This analysis revealed that the deficits experienced by the less skilled comprehenders in both the linguistic and the executive domains could evolve over time. As a result, linguistic factors do not make it possible to distinguish between good and poor comprehenders among the group of older children, whereas the difficulties relating to executive processing remain stable over development. These findings are discussed in the context of the need to take account of the executive difficulties that characterize less skilled comprehenders of any age, especially for remediation purposes.

Fat mass is not beneficial to bone in adolescents and young adults.

CONTEXT: Although muscle mass is beneficial to bone, studies on the effect of fat mass on bone have yielded conflicting results. OBJECTIVE: The aim of this study was to assess the relations between lean and fat mass and bone structure. DESIGN: This study was cross-sectional. SETTING: The study was conducted in a general community. SUBJECTS: Subjects included 300 healthy sexually mature adolescents and young adults (150 males and 150 females) between the ages of 13 and 21 yr. MAIN OUTCOME MEASURE: We investigated the relation between dual-energy x-ray absorptiometry (DXA) measures of total body fat and lean mass and bone values obtained with DXA (legs and lumbar spine bone mineral density and bone mineral content) and computed tomography (CT) (cross-sectional and cortical bone areas of the femurs and cross-sectional area and cancellous bone density of the vertebrae). RESULTS: Simple and multiple linear regression analyses showed significant positive relations between DXA lean mass and all CT and DXA measures of bone in the axial and appendicular skeletons (all P < 0.005). In contrast, whereas Pearson correlations between DXA measures of fat mass and bone parameters were generally positive, multiple regression analyses showed that fat mass, after accounting for lean mass, trunk height/leg length, had a negative, or no, correlation with CT and DXA values for bone. CONCLUSIONS: Our findings provide compelling evidence that, despite increased mechanical loading and independent of lean mass, adipose tissue is not beneficial to bone structure.

Timing of peak bone mass: discrepancies between CT and DXA.

CONTEXT: The time of life in which peak bone mass in the axial skeleton is attained has been the subject of considerable controversy, with estimates ranging from the time of sexual and skeletal maturity to the fifth decade of life. OBJECTIVE: The objective was to examine whether dual energy x-ray absorptiometry (DXA) and computed tomography (CT) values for bone mass and bone density (BD) in the axial skeleton increase after sexual and skeletal maturity. DESIGN/PARTICIPANTS: Measurements of vertebral bone mineral density and bone mineral content (BMC) by DXA and vertebral BD and BMC by CT were obtained in 50 sexually and skeletally mature white females at baseline and 3 yr later. CT BMC values were calculated through analysis of vertebral volume in relation to density (BMC = vertebral volume x BD). RESULTS: Although neither CT BD nor BMC measures changed with time, DXA bone mineral density and BMC values were significantly higher at follow-up (P < 0.0001). Despite strong correlations between DXA and CT bone measures, DXA yielded greater changes in bone values in 47 of 50 subjects. CONCLUSIONS: Bone acquisition in the lumbar spine as measured by CT reaches its peak by sexual and skeletal maturity. In contrast, bone values by DXA continue to increase after puberty and cessation of longitudinal growth. Increases in DXA measures are likely a reflection of inhomogeneous changes in soft tissues around the spine or of disproportionate increases in the posterior elements of the vertebrae rather than of changes within the vertebral body.

Low-level, high-frequency mechanical signals enhance musculoskeletal development of young women with low BMD.

UNLABELLED: The potential for brief periods of low-magnitude, high-frequency mechanical signals to enhance the musculoskeletal system was evaluated in young women with low BMD. Twelve months of this noninvasive signal, induced as whole body vibration for at least 2 minutes each day, increased bone and muscle mass in the axial skeleton and lower extremities compared with controls. INTRODUCTION: The incidence of osteoporosis, a disease that manifests in the elderly, may be reduced by increasing peak bone mass in the young. Preliminary data indicate that extremely low-level mechanical signals are anabolic to bone tissue, and their ability to enhance bone and muscle mass in young women was investigated in this study. MATERIALS AND METHODS: A 12-month trial was conducted in 48 young women (15-20 years) with low BMD and a history of at least one skeletal fracture. One half of the subjects underwent brief (10 minutes requested), daily, low-level whole body vibration (30 Hz, 0.3g); the remaining women served as controls. Quantitative CT performed at baseline and at the end of study was used to establish changes in muscle and bone mass in the weight-bearing skeleton. RESULTS: Using an intention-to-treat (ITT) analysis, cancellous bone in the lumbar vertebrae and cortical bone in the femoral midshaft of the experimental group increased by 2.1% (p = 0.025) and 3.4% (p < 0.001), respectively, compared with 0.1% (p = 0.74) and 1.1% (p = 0.14), in controls. Increases in cancellous and cortical bone were 2.0% (p = 0.06) and 2.3% (p = 0.04) greater, respectively, in the experimental group compared with controls. Cross-sectional area of paraspinous musculature was 4.9% greater (p = 0.002) in the experimental group versus controls. When a per protocol analysis was considered, gains in both muscle and bone were strongly correlated to a threshold in compliance, where the benefit of the mechanical intervention compared with controls was realized once subjects used the device for at least 2 minute/day (n = 18), as reflected by a 3.9% increase in cancellous bone of the spine (p = 0.007), 2.9% increase in cortical bone of the femur (p = 0.009), and 7.2% increase in musculature of the spine (p = 0.001) compared with controls and low compliers (n = 30). CONCLUSIONS: Short bouts of extremely low-level mechanical signals, several orders of magnitude below that associated with vigorous exercise, increased bone and muscle mass in the weight-bearing skeleton of young adult females with low BMD. Should these musculoskeletal enhancements be preserved through adulthood, this intervention may prove to be a deterrent to osteoporosis in the elderly.

Pediatric DXA bone measurements.

Dual-energy x-ray absorptiometry (DXA) has become the most commonly employed technique worldwide for assessment of bone mineral content in adults and children. DXA interpretation in children is more complex because bone dimensions are highly dynamic. Pediatric use of DXA can be used to identify risk of adult osteoporosis. This technology and the increasing knowledge of the genetics, mutations, and mutagens associated with the development of osteoporosis are tools to identify the phenotypes and genotypes in children at risk for osteoporosis later in life, and to design appropriate early interventions for this condition. This paper gives a brief overview of how DXA works, calibration issues, efficacy, safety, and test interpretation.