211 research outputs found
Variation in tibial functionality and fracture susceptibility among healthy, young adults arises from the acquisition of biologically distinct sets of traits
Physiological systems like bone respond to many genetic and environmental factors by adjusting traits in a highly coordinated, compensatory manner to establish organâlevel function. To be mechanically functional, a bone should be sufficiently stiff and strong to support physiological loads. Factors impairing this process are expected to compromise strength and increase fracture risk. We tested the hypotheses that individuals with reduced stiffness relative to body size will show an increased risk of fracturing and that reduced strength arises from the acquisition of biologically distinct sets of traits (ie, different combinations of morphological and tissueâlevel mechanical properties). We assessed tibial functionality retrospectively for 336 young adult women and men engaged in military training, and calculated robustness (total area/bone length), cortical area (Ct.Ar), and tissueâmineral density (TMD). These three traits explained 69% to 72% of the variation in tibial stiffness ( p â<â0.0001). Having reduced stiffness relative to body size (body weightâĂâbone length) was associated with odds ratios of 1.5 (95% confidence interval [CI], 0.5â4.3) and 7.0 (95% CI, 2.0â25.1) for women and men, respectively, for developing a stress fracture based on radiography and scintigraphy. Kâmeans cluster analysis was used to segregate men and women into subgroups based on robustness, Ct.Ar, and TMD adjusted for body size. Stiffness varied 37% to 42% among the clusters ( p â<â0.0001, ANOVA). For men, 78% of stress fracture cases segregated to three clusters ( p â<â0.03, chiâsquare). Clusters showing reduced function exhibited either slender tibias with the expected Ct.Ar and TMD relative to body size and robustness (ie, wellâadapted bones) or robust tibias with reduced residuals for Ct.Ar or TMD relative to body size and robustness (ie, poorly adapted bones). Thus, we show there are multiple biomechanical and thus biological pathways leading to reduced function and increased fracture risk. Our results have important implications for developing personalized preventative diagnostics and treatments.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98270/1/jbmr1879.pd
Increased density and periosteal expansion of the tibia in young adult men following short-term arduous training
Purpose: Few human studies have reported early structural adaptations of bone to weight-bearing exercise, which provide a greater contribution to improved bone strength than increased density. This prospective study examined site- and regional-specific adaptations of the tibia during arduous training in a cohort of male military (infantry) recruits to better understand how bone responds in vivo to mechanical loading. Methods: Tibial bone density and geometry were measured in 90 British Army male recruits (ages 21 + 3 y, height 1.78 ± 0.06 m, body mass 73.9 + 9.8 kg) in weeks 1 (Baseline) and 10 of initial military training. Scans were performed at the 4%, 14%, 38% and 66% sites, measured from the distal end plate, using pQCT (XCT2000L, Stratec Pforzheim, Germany). Customised software (BAMPack, L-3 ATI) was used to examine whole bone cross-section and regional sectors. T-tests determined significant differences between time points (P<0.05). Results: Bone density of trabecular and cortical compartments increased significantly at all measured sites. Bone geometry (cortical area and thickness) and bone strength (i, MMi and BSI) at the diaphyseal sites (38 and 66%) were also significantly higher in week 10. Regional changes in density and geometry were largely observed in the anterior, medial-anterior and anterior-posterior sectors. Calf muscle density and area (66% site) increased significantly at week 10 (P<0.01). Conclusions: In vivo mechanical loading improves bone strength of the human tibia by increased density and periosteal expansion, which varies by site and region of the bone. These changes may occur in response to the nature and distribution of forces originating from bending, torsional and shear stresses of military training. These improvements are observed early in training when the osteogenic stimulus is sufficient, which may be close to the fracture threshold in some individuals
Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV
A search for pair-production of supersymmetric particles under the assumption
that R-parity is violated via a dominant LQDbar coupling has been performed
using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV.
The observed candidate events in the data are in agreement with the Standard
Model expectation. This result is translated into lower limits on the masses of
charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for
m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81
GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the
95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure
Search for oscillations using inclusive lepton events
A search for Bs oscillations is performed using a sample of semileptonic b-hadron decays collected by the ALEPH experiment during 1991-1995. Compared to previous inclusive lepton analyses, the prop er time resolution and b-flavour mistag rate are significantly improved. Additional sensitivity to Bs mixing is obtained by identifying subsamples of events having a Bs purity which is higher than the average for the whole data sample. Unbinned maximum likelihood amplitude fits are performed to derive a lower limit of Dms>9.5 ps-1 at 95% CL. Combining with the ALEPH Ds based analyses yields Dms>9.6 ps-1 at 95% CL.A search for B0s oscillations is performed using a sample of semileptonic b-hadron decays collected by the ALEPH experiment during 1991-1995. Compared to previous inclusive lepton analyses, the proper time resolution and b-flavour mistag rate are significantly improved. Additional sensitivity to B0s mixing is obtained by identifying subsamples of events having a B0s purity which is higher than the average for the whole data sample. Unbinned maximum likelihood amplitude fits are performed to derive a lower limit of Deltam_s>9.5ps^-1 at 95% CL. Combining with the ALEPH D-s based analyses yields Deltam_s>9.6ps^-1 at 95% CL
Measurement of the W mass in collisions at 183 GeV
The mass of the W boson is obtained from reconstructed invariant mass distributions in W-pair events. The sample of W pairs is selected from 57 pb collected with the ALEPH detector in 1997 at a centre-of-mass energy of 183 GeV. The invariant mass distributions of reweighted Monte Carlo events are fitted separately to the experimental distributions in the and all l\nuqqbar channels to give the following W masses: , where the theory error represents the possible effects of final state interactions. The combination of these two measurements, including the LEP energy calibration uncertainty, gives $m_{W} = 80.393 \pm 0.128(stat.)\pm 0.041(syst.) \pm 0.028(theory)\pm 0.021(LEP) GeV/c^2
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