Colin E. Webber

Exercise and bone mineral density.

SummaryA decrease in physical activity may lead to an increased loss of bone and an increase in the incidence of osteoporotic fractures. Studies have demonstrated increases in bone formation in animals and increases in bone mineral density in humans. Studies of animals show that bone has enhanced physical and mechanical properties following periods of increased stress. Strains which are high in rate and magnitude, and of abnormal distribution, but not necessarily long in duration, are best for inducing new bone formation, resulting in the strengthening of bone by increased density. Cross-sectional studies show that athletes, especially those who are strength-trained, have greater bone mineral densities than nonathletes, and that strength, muscle mass and maximal oxygen uptake correlate with bone density. Longitudinal training studies indicate that strength training and high impact endurance training increase bone density.Strain induction, the deformation that occurs in bone under loading, may cause a greater level of formation and an inhibition of resorption within the normal remodelling cycle of bone, or it may cause direct activation of osteoblastic bone formation from the quiescent state.Various mechanisms have been proposed for the transformation of mechanical strain into biochemical stimuli to enhance bone formation. These include prostaglandin release, piezoelectric and streaming potentials, increased bone blood flow, microdamage and hormonally mediated mechanisms. These mechanisms may act on their own or in concert, depending on the loading situation and the characteristics of the bone.

A comparison of strength and muscle mass increases during resistance training in young women

Abstract Strength gains with resistance training are due to muscle hypertrophy and nervous system adaptations. The contribution of either factor may be related to the complexity of the exercise task used during training. The purpose of this investigation was to measure the degree to which muscle hypertrophy contributes to gains in strength during exercises of varying complexity. Nineteen young women resistance trained twice a week for 20 weeks, performing exercises designed to provide whole-body training.The lean mass of the trunk, legs and arms was measured by dual energy x-ray absorptiometry and compared to strength gains (measured as the 1-repetition maximum) in bench press, leg press and arm curl exercises, pre-, mid- (10 weeks) and post-training. No changes were found in a control group of ten women. For the exercise group, increases in bench press, leg press and arm curl strength were significant from pre- to mid-, and from mid- to post-training (P < 0.05). In contrast, increases in the lean mass of the body segments used in these exercises followed a different pattern. Increases in the lean mass of the arms were significant from pre- to mid-training, while increases in the lean mass of the trunk and legs were delayed and significant from mid- to post-training only (P < 0.05). It is concluded that a more prolonged neural adaptation related to the more complex bench and leg press movements may have delayed hypertrophy in the trunk and legs. With the simpler arm curl exercise, early gains in strength were accompanied by muscle hypertrophy and, presumably, a faster neural adaptation.

Gymnastic training and bone density in pre-adolescent females

Bone mineral density (BMD) was compared between 7-11-yr-old female gymnasts (GYM: N = 16) with a history of high volume impact loading (minimum of 15 h.wk-1 for past 2 yr) and healthy nonathletic controls (CON: N = 16). Whole body (WB) and regional areal BMD measures were determined by dual energy x-ray absorptiometry (DXA) normalized for height and body mass and also converted to bone mineral apparent density (BMAD). Volumetric BMD and bone cross-sectional areas were also measured by peripheral QCT (pQCT) at the left distal radius. GYM were significantly (P < 0.01) shorter (129.3 +/- 5.7 vs 136.7 +/- 4.4 cm; means +/- SD) and leaner (15.1 +/- 1.9 vs 19.6 +/- 4.3% body fat from DXA), and had significantly (P < 0.05) greater femoral neck (0.698 +/- 0.058 vs 0.648 +/- 0.064 g.cm-2) and trochanter (0.616 +/- 0.060 vs 0.530 +/- 0.084 g.cm-2) areal BMD than CON. GYM also had significantly higher whole body (0.101 +/- 0.009 vs 0.094 +/- 0.007 g.cm-3), femoral neck (0.245 +/- 0.060 vs 0.205 +/- 0.049 g.cm-3) and lumbar spine (0.227 +/- 0.014 vs 0.210 +/- 0.026 g.cm-3) BMAD compared with CON. Height normalized areal BMD measures were also significantly higher at all sites in GYM. Radial total (367.7 +/- 51.6 vs 307.4 +/- 27.6 mg.cm-3), trabecular (207.9 +/- 45.3 vs 163.8 +/- 31.4 mg.cm-3), and cortical (496.9 +/- 67.5 vs 429.8 +/- 33.8 mg.cm-3) BMD were also significantly greater in the GYM compared with the CON. In conclusion, high volume impact loading was associated with greater (compared with controls) whole body and regional bone mineral density in pre-adolescent female gymnasts.

Partition of circulating lead between serum and red cells is different for internal and external sources of lead

Serum lead, whole blood lead, and lead in both tibia and calcaneus were measured in each of 49 active lead workers. Serum lead correlated more strongly with both in vivo bone lead measurements than did whole blood lead. The ratio of serum lead to whole blood lead varied from 0.8% to 2.5% and showed a positive correlation with tibia, and an even stronger correlation with calcaneus lead. This implies that lead released from bone (endogenous exposure) results in a higher proportion of whole blood lead being in serum than is the case for exogenous exposure. This observation needs to be confirmed, and the relationships amongst the parameters must be studied further, particularly in former or retired lead workers. If confirmed, since at least a portion of lead in serum is readily diffusible and thus toxicologically more immediately significant than lead bound to red cells, the health implications of endogenous exposure may have to be reassessed.

In vivo assessment of trabecular bone structure at the distal radius from high-resolution computed tomography images

A dedicated computed tomography system was used to acquire transaxial images of the distal radius to assess trabecular bone structure in vivo. We segmented trabecular bone from the marrow and soft tissue background by postprocessing the image with a region grow and skeletonization step. From the processed image we assessed the integrity of the bone by examining the continuity of its trabecular network and by determining the area of the holes comprising its marrow space. The continuity of the bone imaged was assessed by a proposed connectivity index (CI) and the size of the marrow spaces was assessed by calculating a mean hole area (H(A)) in the bone cross-section. Repeat measurements revealed that the intra-subject variability in CI and H(A) was small (CV < 6%). Both CI and H(A) were sensitive enough to reflect differences in structure at the head of the radius and at several sites along its shaft. We tested the diagnostic value of assessing bone structure at the distal end of the radius by measuring trabecular bone density, CI and H(A) in a mixed group of 26 subjects, nine of whom had suffered a wrist fracture. We found that a trabecular bone density threshold of 116 mg cm-3, corresponding to two standard deviations below the mean density in the 17 non-fractured subjects, separated fractured from non-fractured subjects with a sensitivity of 22% and a specificity of 100%. A CI threshold of -4.7 doubled the sensitivity (44%) and maintained the 100% specificity. An H(A) threshold of 4.5 mm2 achieved a sensitivity of 89% and a specificity of 94%. This increased sensitivity achieved by our indices suggests that an in vivo assessment of trabecular bone structure can contribute significantly to the identification of persons at risk of fracture.

In vivo assessment of trabecular bone structure at the distal radius from high‐resolution magnetic resonance images

In this study a method of assessing trabecular bone structure at the distal end of the radius from high-resolution magnetic resonance images is described. Trabecular bone is segmented from the marrow and soft tissue background using an adaptive threshold, a region growth, and a skeletonization step. From the processed image we measured the connectivity and orientation of the trabecular bone network. Connectivity was assessed by a proposed connectivity index (CI) and marrow space was quantitated by a mean hole area (HA). Significant age-related changes in CI and HA were observed in a mixed group of normal volunteers. CI decreased at a rate of 0.18 yr-1 (r = 0.72, n = 14, p < 0.05) and HA increased at a rate of 0.018 mm2 yr-1 (r = 0.69, n = 14, p < 0.05). Gradient analysis was used to examine trabecular orientation, and revealed that the individual trabeculae at the distal end of the radius are organized anisotropically along the bone. These findings suggest that clinical magnetic resonance scanners can be used to assess trabecular bone structure in vivo.

Osteopenia, physical activity and health‐related quality of life in survivors of brain tumors treated in childhood

Osteopenia has been reported in children surviving acute lymphoblastic leukemia and brain tumors, apparently as a consequence of therapy. It has been suggested that cranial irradiation may play a role in the development of this complication. In order to explore that possibility, we examined survivors of brain tumors treated with and without radiation in childhood to investigate associations between radiation, osteopenia, physical activity, health status and overall health‐related quality of life (HRQL).

Bone Density Measured by Photon Scattering. I. A System for Clinical Use

A system for the routine measurement of the density of the os calcis is described. Measurements are made of the number of photons scattered by the bone from a 153Sm photon beam. The first results from human subjects are presented.

Further experience with bone lead content measurements in residents of southern Ontario.

Bone lead content of the mid-tibia was measured by in vivo fluorescence excitation in 90 females and 59 males aged between 6 and 81. The cross-sectionally derived rate of increase of tibia lead content was 0.24 +/- 0.03 microgram [g mineral]-1 yr-1. In 93 adult women, the corresponding rate of increase for calcaneus lead content was 0.12 +/- 0.11 microgram [g mineral]-1 yr-1. Comparison with European values show that, in Canada, the rates of lead accumulation are greater than those found in N. Sweden and Finland, similar to those of S. Sweden and less than values measured in England.

Coherent scattering and the assessment of mineral concentration in trabecular bone

The number of 103.2 keV (153Sm) gamma-rays scattered coherently and incoherently from the os calcis of three cadaver feet has been measured using a high purity Ge detector. The ratio of the intensities of coherent to incoherent scattered photons is dependent on elemental composition while the number scattered incoherently is dependent on density. The results indicate that techniques for the assessment of mineral status in the skeleton may be based on either of these measurements and each will exhibit a similar sensitivity to a given biological change. It is shown that a method based entirely on the detection of coherently scattered photons will be more sensitive to changes in mineral composition than either of the above. Such a system is proposed and optimised with respect to incident beam energy and scattering angle. For a dose of 4 mSV, coherent intensity measurements with a precision of 3% are anticipated.