Fat and muscle indices assessed by pQCT: relationships with physical activity and type 2 diabetes risk.

The aim of this study was to compare and determine the repeatability of foreleg and forearm muscle and fat indices evaluated by the peripheral quantitative computed tomography (pQCT). Effects of habitual physical activity and associated health risk of type 2 diabetes were examined within the interrelations of intermuscular adipose tissue (IMAT) and muscle density. Eighty-two premenopausal women (mean age ± standard deviation: 38.6 ± 4.7 yr) underwent dual-energy X-ray absorptiometry scans and pQCT of foreleg and forearm scans to assess muscle and fat parameters. Physical activity status was based on 4-d self-reported log and pedometer step counts. Fat and muscle distribution between the foreleg and forearm were similar and highly correlated to total body adiposity. The pQCT device reliably measured muscle density in the foreleg and forearm; coefficients of variation were 0.8% and 2.1%, which was therefore used to reflect IMAT status. Muscle density was positively related to physical activity and negatively associated with markers of fat distribution and risk for type 2 diabetes. The pQCT is a novel, noninvasive tool to assess IMAT and muscle density in the foreleg and forearm. Additional research is necessary to understand the biology of IMAT and its relations with physical activity and potentially, with risks for cardiometabolic disease.

Isokinetic resistance training increases tibial bending stiffness in young women.

Bone mineral content (BMC) and bone mineral density (BMD) are common but imperfect surrogate measures of bone strength. The mechanical response tissue analyzer is a device that measures long bone bending stiffness (EI), which strongly predicts bone breaking strength. We hypothesized that isokinetic resistance training of the knee flexor and extensor muscles would increase tibial EI, BMC, and BMD in young women. Fifty-two women, aged 18-26 years, performed concentric (CON, n = 30) or eccentric (ECC, n = 22) isokinetic resistance training with the nondominant leg three times per week for 20 weeks. Before and after the training period, subjects were tested for CON and ECC peak torque of the knee flexor and extensor muscles with isokinetic dynamometry, tibial BMC and BMD using dual-energy X-ray absorptiometry, and tibial EI using mechanical response tissue analysis. Both training groups increased CON (15-21%) and ECC (17-31%) peak torque vs. the untrained leg. Tibial EI increased in the entire cohort (26%) and in each training group (CON 34%, ECC 16%) vs. the untrained tibia. Tibial BMC and BMD increased in the trained and untrained tibiae, with no significant differences between limbs. No differential tibial EI or bone mineral outcomes were observed between the CON and ECC training groups. In summary, CON and ECC isokinetic resistance training increased tibial EI, but not BMC or BMD, in young women.

Age influences anthropometric and fitness-related predictors of bone mineral in men.

OBJECTIVE: This study assessed the influence of age on the predictors of bone mineral in men. METHODS: Middle-age (n = 41, 54 +/- 4 yrs) and older (n = 40, 69 +/- 5 yrs) men underwent grip and knee extensor strength tests, total body dual-energy X-ray absorptiometry with regional analyses and a graded exercise treadmill test. RESULTS: Bone-free lean mass (BFLM) and, to a lesser extent, fat mass (FM) were correlated with bone mineral variables in middle-age men. In older men, BFLM and, to a lesser extent, FM were related to bone mineral content (BMC) at most sites, but inconsistently to bone mineral density (BMD). Knee extensor strength related to bone mineral (BMC and BMD) at most sites in middle-age men, but none in older men. Grip strength inconsistently related to bone mineral in both groups. Aerobic capacity related to bone mineral in middle-age men, but none in older men. In multiple regression, body weight or BFLM predicted bone mineral in middle-age men (R2 = 0.33-0.68) and BMC in older men (R2 = 0.33-0.50). Predictors of BMD were inconsistent in older men. CONCLUSIONS: Relationships of body composition, muscular strength and aerobic capacity to bone mineral are stronger in middle-age versus older men.

Isokinetic training increases ulnar bending stiffness and bone mineral in young women.

Numerous studies have investigated the effects of physical activity on bone health; however, little is known about the effects of isokinetic strength training on bone. While bone mineral density (BMD) is widely used to assess bone health and fracture risk, there are several limitations of this measure that warrant new technology development to measure bone strength. The mechanical response tissue analyzer (MRTA) assesses bone strength by measuring maximal bending stiffness (EI). We hypothesized that isokinetic strength training of the elbow flexors and extensors would increase ulnar EI, BMD, and bone mineral content (BMC) in young women. Fifty-four women trained the nondominant arm 3 times per week for 20 weeks; 32 trained concentrically (CON) and 22 trained eccentrically (ECC). Subjects were assessed for the following variables pre- and post-training: CON and ECC peak torque of the elbow flexors and extensors with isokinetic dynamometry, ulnar mineral content and density using dual-energy X-ray absorptiometry, and ulnar EI using MRTA. Isokinetic training increased CON (17%) and ECC (17%) peak torque, even when controlling for changes in the untrained arm. Eccentric training increased CON and ECC peak torque while CON training improved CON peak torque only. Isokinetic training increased ulnar EI 28%, which was statistically greater than the untrained arm. Ulnar EI increased 25% with CON training and 32% with ECC training. Both training modes resulted in greater EI gains compared to the untrained limb. Isokinetic training increased ulnar BMC (2.7%) and BMD (2.3%), even when controlling for untrained ulna changes. Both training modalities resulted in BMC and BMD increases; however, only CON training yielded gains when controlling for changes in the untrained limb. In conclusion, isokinetic strength training increases ulnar EI, BMC, and BMD in young women; no statistical differences were noted between CON and ECC training modes.

Changes in bone mineral and body composition following coronary artery bypass grafting in men.

This study investigated bone mineral and body composition changes after coronary artery bypass grafting (CABG) in men. Twenty-six men 50 to 79 years of age underwent CABG for multivessel coronary disease. Dual-energy x-ray absorptiometry was performed before surgery and 3 months and 1 year after treatment to assess bone mineral content (BMC), bone mineral density (BMD), and body composition. Through 3 months after treatment, BMD decreased at the total body, arms, and pelvis. BMC of the arm decreased and losses at the total body and legs approached significance. Fat-free mass decreased in the arms and total body but not in the legs. Neither total body nor regional fat mass changed. At the 1-year follow-up visit, 15 of the initial 26 subjects returned for dual-energy x-ray absorptiometry. Compared with before treatment, BMD decreased at the total body and legs, whereas losses at the arms approached significance. Arm BMC decreased over the 1-year post-treatment period. No changes were observed in body composition. In conclusion, CABG and the ensuing convalescence period results in considerable arm bone mineral losses through 1 year after treatment.

Distal tibia areal bone mineral density: use in detecting low aBMD of the hip in young women.

Dual-energy X-ray absorptiometry (DXA) is a primary clinical tool for identification of adults with low areal bone mineral density (aBMD) and who are at increased risk for future osteoporosis and fragility fractures. Procedures for several aBMD scans of clinical interest might be limited by artifact, inaccessible anatomical regions, and positioning errors. Sites for scanning that overcome these limitations need further investigation for application to large-scale screening and relevance to clinical decisions regarding diagnosis and treatment. In this study, 146 women (mean +/- SE age = 20.1 +/- 0.1 yr, height = 163.3 +/- 0.2 cm, weight = 60.0 +/- 0.2 kg) underwent DXA of the total body (TB) and right and left total proximal femurs (TPF), total forearms (TF), and distal tibiae (DT). Osteopenia was identified in 24 women. Areal BMD was positively related among all measurement sites (r = 0.55-0.81, all p < 0.001). Total body, TF, and DT aBMD each displayed low sensitivity (0.29-0.33) and high specificity (0.95-0.98) to detect osteopenia of the TPF. Addition of TB fat-free mass slightly enhanced the predictive value of DT aBMD. Overall, DT aBMD can discriminate between osteopenic and normal subjects with comparable accuracy to TB or TF aBMD.

Recovery of self-reported functional capacity after coronary artery bypass surgery.

STUDY OBJECTIVES: This study was conducted to determine the effects of age, gender, comorbid conditions, and exercise on the recovery of self-reported functional capacity after coronary artery surgery, and to identify predictors of 1-year functional capacity. PATIENTS: One hundred ninety-eight patients undergoing coronary artery bypass graft surgery. MEASUREMENTS AND RESULTS: Self-reported functional capacity was evaluated before surgery, and 3 months and 1 year postoperatively using the Veterans Specific Activity Questionnaire (VSAQ). Patients were classified into groups based on age, gender, comorbid conditions, and postoperative exercise. Repeated-measures analysis of variance was used to determine if groups differed with respect to functional capacity recovery and multiple linear regression was used to identify predictors of 1-year VSAQ score. A significant time by age interaction was found (p = 0.0001), with a more protracted recovery for older patients. There were significant group effects for gender (p = 0.0001), and presence of comorbid conditions (p = 0.0009); however, there were no time/group interactions for these variables. A significant group effect was found for postoperative exercise (p = 0.0001), with a trend toward group/time interaction (p = 0.096). Predictors of 1-year functional capacity were VSAQ score in the year prior to surgery and performance of regular aerobic exercise in the postoperative period. CONCLUSIONS: This study suggests that older patients attain good self-reported functional outcomes after surgery; however, the time course for recovery is more protracted than for younger patients. Functional capacity in the year prior to surgery and postoperative exercise are key predictors of 1-year functional capacity.

Bone mineral density in postmenopausal women: does exercise training make a difference?

Although postmenopausal women are encouraged to exercise to preserve bone mineral density (BMD), few studies have looked at what type of exercise is most effective.

Rationale, design and clinical performance of the mechanical response tissue analyser: a non-invasive technology for measurement of long bone bending stiffness.

Prediction of osteoporotic fractures is currently an imperfect science and new tools are desperately needed to identify at-risk patients at an earlier stage in the disease process. The mechanical response tissue analyser (MRTA) is a novel, non-invasive, radiation-free device that measures the bending stiffness of long bones in vivo, an indicator of a bone's ability to resist deformation under a given load and a strong predictor of long bone structural integrity and strength. Bone bending stiffness measured with the MRTA has been consistently shown to be a stronger predictor of post-mortem and ex vivo bone breaking strength compared to bone mineral measured with dual-energy X-ray absorptiometry. Bone bending stiffness measured with MRTA also decreases with advanced age and disease states and increases with chronic physical activity, independent of bone mineral changes. The MRTA measures different parameters than DXA (bone quality vs bone mineral content and density) and may be a more robust tool for identifying those at risk for fracture. Research initiatives focused on improving long-term repeatability and optimizing the signal-to-noise ratio of the measurement are currently underway to further advance the clinical usefulness of this technology.

Genomewide molecular and biologic characterization of biomembrane formation adjacent to a methacrylate spacer in the rat femoral segmental defect model.

OBJECTIVES: This study focuses upon the morphologic and molecular features of the layer of cells, termed the "biomembrane," which forms around methacrylate spacers in bone segmental defects. The objective of this research was to assess the biomembrane formed in a novel rodent femoral segmental defect model at 4, 8, and 16 weeks with histologic and molecular studies. METHODS: Following Institutional Animal Care and Use Committee approval, a segmental defect was created in the rat femur and stabilized with the AO LockingRatNail and analyzed at 4, 8, and 16 weeks postsurgery using digital radiologic imaging, morphological and immunohistochemical studies, and genomewide gene expression studies employing microarray analysis. RESULTS: The biomembrane formed around the methacrylate spacer was rich in vasculature, which showed vascular endothelial growth factor immunolocalization. The biomembrane supported development of foci of bone and cartilage within it. Bone morphogenetic protein 2 immunolocalization and gene expression were positive within developing osseous and chondrocyte foci. Microarray analysis showed significant expression of key genes related to bone and cartilage formation and angiogenesis. CONCLUSIONS: This rat bone model was effective in creation of the biomembrane. Bone and cartilage foci were formed within the vascularized biomembrane with associated expression of genes critical for bone and cartilage development/formation and vascularization. The polymethyl methacrylate-induced biomembrane offers an exciting potential solution for segmental defects; the biomembrane, may act as a receptive bed and also serve as a source for mesenchymal stem cells, which could be recruited/directed for the healing process.

Osteogenic and chondrogenic potential of biomembrane cells from the PMMA-segmental defect rat model.

A layer of cells (the "biomembrane") has been identified in large segmental defects between bone and surgically placed methacrylate spacers or antibiotic-impregnated cement beads. We hypothesize that this contains a pluripotent stem cell population with potential valuable applications in orthopedic tissue engineering. Objectives using biomembranes harvested from rat segmental defects were to: (1) Culture biomembrane cells in specialized media to direct progenitor cells along bone or cartilage cell differentiation lineages; (2) evaluate harvested biomembranes for mesenchymal stem cell markers, and (3) define relevant gene expression patterns in harvested biomembranes using microarray analysis. Culture in osteogenic media produced mineralized nodules; culture in chondrogenic media produced masses containing chondroitin sulfate/sulfated proteoglycans. Molecular analysis of biomembrane cells versus control periosteum showed significant upregulation of key genes functioning in mesenchymal stem cell differentiation, development, maintenance, and proliferation. Results identified significant upregulation of WNT receptor signaling pathway genes and significant upregulation of BMP signaling pathway genes. Findings confirm that the biomembrane has a pluripotent stem cell population. The ability to heal large bone defects is clinically challenging, and novel tissue engineering uses of the biomembrane hold great promise in treating non-unions, open fractures with large bone loss and/or infections, and defects associated with tumor resection.

A review of weight loss following Roux-en-Y gastric bypass vs restrictive bariatric surgery: impact on adiponectin and insulin.

BACKGROUND: Bariatric surgery is a common procedure often used to ameliorate comorbidities associated with obesity, including type 2 diabetes. Substantial weight loss leads to alterations in inflammation and insulin sensitivity as well as numerous metabolic and physiologic pathways. Several inflammatory markers have been evaluated, yet adiponectin, an anti-inflammatory adipokine, has not been fully investigated. Adiponectin may play a key role as a mediator between obesity and inflammation, as lower blood levels are more commonly associated with obesity and type 2 diabetes and because adiponectin lessens insulin resistance. This review evaluates outcome variables from patients who underwent Roux-en-Y gastric bypass (RYGB) or restrictive bariatric surgery to compare and contrast any differential surgical impacts on weight loss, adiponectin, and insulin. METHODS: A systematic literature review was conducted using a PubMed search. Published studies from 1999 to 2009 that measured blood levels of adiponectin and insulin in bariatric surgery patients prior to and at least 6 months after surgery were included. RESULTS: Eighteen studies met inclusion criteria for evaluation. RYGB surgery compared to restrictive surgery led to significantly greater weight loss and improvements in adiponectin and insulin sensitivity. Despite significant weight loss, many patients did not achieve "healthy" body mass index or normalization of inflammatory markers. CONCLUSIONS: While RYGB surgery appears to more favorably influence body weight and inflammatory markers, data are insufficient to fully understand the impact of bariatric surgery on changes in adiponectin and insulin and related health implications. Long-term research is needed to more thoroughly evaluate inflammatory outcomes following these two bariatric surgery procedures.

Knee extensor and flexor torque development with concentric and eccentric isokinetic training.

This study assessed muscular torque and rate of torque development following concentric (CON) or eccentric (ECC) isokinetic training. Thirty-eight women were randomly assigned to either CON or ECC training groups. Training consisted of knee extension and flexion of the nondominant leg three times per week for 20 weeks (SD = 1). Eccentric training increased ECC knee extension and flexion peak torque more than CON training. The ECC group improved acceleration time and time to peak torque with ECC movements versus the CON group. Slow-velocity ECC isokinetic training yielded greater ECC and similar CON torque development gains versus CON training over the course of 20 weeks in young women.