Prevention of postmenopausal bone loss by a low-magnitude, high-frequency mechanical stimuli: a clinical trial assessing compliance, efficacy, and safety

Mechanical Signals As a Non-Invasive Means to Influence Mesenchymal Stem Cell Fate, Promoting Bone and Suppressing the Fat Phenotype

Pluripotent mesenchymal stem cells (MSCs) are considered ideal therapeutic targets in regenerative medicine, as they hold the capacity to differentiate into higher order connective tissues. The potential to harness MSCs for disease treatment and acceleration of repair will ultimately depend on an improved understanding of how physical and/or chemical signals regulate their activity, and the ability of exogenous stimuli to enhance MSC proliferation and define MSC fate. Recent appreciation that bone marrow osteoprogenitors are inversely proportional to adipocyte precursors suggests that their shared progenitor, the MSC, will commit to one lineage at the cost of the other. This interrelationship may contribute to the phenotype of sedentary subjects who have more fat and less bone, while conversely, to the outcome of exercise being less fat and more bone. Mechanical biasing of MSC lineage selection suggests that physical signals may influence the quantity of both fat and bone through developmental, as well as metabolic or adaptive pathways. Considered with the recent finding that low magnitude mechanical signals (LMMS) suppress the development of subcutaneous and visceral fat without elevating energy expenditure, this indicates that MSCs are ideally positioned as mechanosensitive elements central to musculoskeletal adaptation, but that the signals needn't be large to be influential. The biasing of MSC differentiation by mechanical signals represents a unique means by which adiposity can be inhibited while simultaneously promoting a better skeleton, and may provide the basis for a safe, non-invasive, non-pharmacologic strategy to prevent both obesity and osteoporosis, yet uniquely - without targeting the resident fat or bone cell.

Extremely small-magnitude accelerations enhance bone regeneration: a preliminary study

High-frequency, low-magnitude accelerations can be anabolic and anticatabolic to bone. We tested the hypothesis that application of these mechanical signals can accelerate bone regeneration in scaffolded and nonscaffolded calvarial defects. The cranium of experimental rats (n = 8) in which the 5-mm bilateral defects either contained a collagen scaffold or were left empty received oscillatory accelerations (45 Hz, 0.4 g) for 20 minutes per day for 3 weeks. Compared with scaffolded defects in the untreated control group (n = 6), defects with a scaffold and subject to oscillatory accelerations had a 265% greater fractional bone defect area 4 weeks after the surgery. After 8 weeks of healing (1-week recovery, 3 weeks of stimulation, 4 weeks without stimulation), the area (181%), volume (137%), and thickness (53%) of the regenerating tissue in the scaffolded defect were greater in experimental than in control animals. In unscaffolded defects, mechanical stimulation induced an 84% greater bone volume and a 33% greater thickness in the defect. These data provide preliminary evidence that extremely low-level, high-frequency accelerations can enhance osseous regenerative processes, particularly in the presence of a supporting scaffold.

Short-term exercise in mice increases tibial post-yield mechanical properties while two weeks of latency following exercise increases tissue-level strength

We have previously shown that exercise during growth increases post-yield deformation in C57BL6/129 (B6;129) male tibiae at the expense of reduced pre-yield deformation and structural and tissue strength. Other research in the literature indicates that increased mineral content, cross-sectional geometry and structural strength due to exercise can be maintained or increased after exercise ends for as long as 14 weeks. It was therefore hypothesized that after our exercise protocol ended, effects of exercise on mechanical properties would persist, resulting in increased post-yield behavior and rescued strength versus age-matched control mice. Beginning at 8 weeks of age, exercise consisted of running on a treadmill (30 min/day, 12 m/min, 5 degrees incline) for 21 consecutive days. At the end of running and 2 weeks later, in the cortical bone of the tibial mid-diaphyses of B6;129 male mice, changes due to exercise and latency following exercise were assayed by mechanical tests and analyses of cross-sectional geometry. Exercise increased structural post-yield deformation compared with weight-matched control mice, without changes in bone size or shape, suggesting that exercised-induced changes in pre-existing bone quality were responsible. Over the 2-week latency period, no growth-related changes were noted in control mice, but exercise-induced changes resulted in increased tissue stiffness and strength versus mice sacrificed immediately after exercise ended. Our data indicate that periods of exercise followed by latency can alter strength, stiffness, and ductility of bone independent of changes in size or shape, suggesting that exercise may be a practical way to increase the quality of the bone extracellular matrix.

Low magnitude and high frequency mechanical loading prevents decreased bone formation responses of 2T3 preosteoblasts

Bone loss due to osteoporosis or disuse such as in paraplegia or microgravity is a significant health problem. As a treatment for osteoporosis, brief exposure of intact animals or humans to low magnitude and high frequency (LMHF) mechanical loading has been shown to normalize and prevent bone loss. However, the underlying molecular changes and the target cells by which LMHF mechanical loading alleviate bone loss are not known. Here, we hypothesized that direct application of LMHF mechanical loading to osteoblasts alters their cell responses, preventing decreased bone formation induced by disuse or microgravity conditions. To test our hypothesis, preosteoblast 2T3 cells were exposed to a disuse condition using the random positioning machine (RPM) and intervened with an LMHF mechanical load (0.1-0.4 g at 30 Hz for 10-60 min/day). Exposure of 2T3 cells to the RPM decreased bone formation responses as determined by alkaline phosphatase (ALP) activity and mineralization even in the presence of a submaximal dose of BMP4 (20 ng/ml). However, LMHF mechanical loading prevented the RPM-induced decrease in ALP activity and mineralization. Mineralization induced by LMHF mechanical loading was enhanced by treatment with bone morphogenic protein 4 (BMP4) and blocked by the BMP antagonist noggin, suggesting a role for BMPs in this response. In addition, LMHF mechanical loading rescued the RPM-induced decrease in gene expression of ALP, runx2, osteomodulin, parathyroid hormone receptor 1, and osteoglycin. These findings suggest that preosteoblasts may directly respond to LMHF mechanical loading to induce differentiation responses. The mechanosensitive genes identified here provide potential targets for pharmaceutical treatments that may be used in combination with low level mechanical loading to better treat osteoporosis or disuse-induced bone loss.

Fluid and Solute Transport in Bone: Flow-Induced Mechanotransduction

Much recent evidence suggests that bone cells sense their mechanical environment via interstitial fluid flow. In this review, we summarize theoretical and experimental approaches to quantify fluid and solute transport in bone, starting with the early investigations of fluid shear stress applied to bone cells. The pathways of bone interstitial fluid and solute movement are high-lighted based on recent theoretical models, as well as a new generation of tracer experiments that have clarified and refined the structure and function of the osteocyte pericellular matrix. Then we trace how the fluid-flow models for mechanotransduction have evolved as new ultrastructural features of the osteocyte lacunar-canalicular porosity have been identified and how more recent in vitro fluid-flow and cell-stretch experiments have helped elucidate at the molecular level the possible pathways for cellular excitation in bone.

The establishment of a mechanobiology model of bone and functional adaptation in response to mechanical loading

BACKGROUND

Mechanical stimuli affected bone adaptation, however, the mechanism on a dose-response relationship between mechanical stimuli and bone response is unclear. Therefore, we established a mechanobiology model to evaluated the adaptive response of bone to strain deformation at high-frequencies (5-15 Hz) of externally applied strain.

METHODS

The ulnae of adult female rats were subjected to dynamic axial loading in vivo using Instron materials-testing machine. The applied loading at frequencies of 5 Hz, 10 Hz, and 15 Hz for 10 min with a haversine, low-magnitude waveform for a 2 weeks period, the peak strains is 2000 muepsilon and 3000 muepsilon. Strain was recorded using strain gauge conditioner and compared to physiological values obtained after testing.

FINDINGS

At frequencies of 10 Hz, 15 Hz groups, loading promoted obviously secreted of osteocalcin and collagen; a relative benefit in Bone Mineral Density (BMD) was found compare to the control (P < 0.05) followed the decline of material mechanical properties (modulus of elasticity, ultimate stress) (P < 0.01).

INTERPRETATION

These data show that a mechanobiology model of the axial ulna loading technique had been established successfully in rat. A short daily period of low-magnitude, high-frequency mechanical stimuli results in an osteogenic response related to peak strain magnitude, which do not result in significant differences in mechanical properties between the groups.

Effects of whole body vibration on the skeleton and other organ systems in man and animal models: what we know and what we need to know

Previous investigations reported enhanced osseous parameters subsequent to administration of whole body vibration (WBV). While the efficacy of WBV continues to be explored, scientific inquiries should consider several key factors. Bone remodeling patterns differ according to age and hormonal status. Therefore, WBV protocols should be designed specifically for the subject population investigated. Further, administration of WBV to individuals at greatest risk for osteoporosis may elicit secondary physiological benefits (e.g., improved balance and mobility). Secondly, there is a paucity of data in the literature regarding the physiological modulation of WBV on other organ systems and tissues. Vibration-induced modulation of systemic hormones may provide a mechanism by which skeletal tissue is enhanced. Lastly, the most appropriate frequencies, durations, and amplitudes of vibration necessary for a beneficial response are unknown, and the type of vibratory signal (e.g., sinusoidal) is often not reported. This review summarizes the physiological responses of several organ systems in an attempt to link the global influence of WBV. Further, we report findings focused on subject populations that may benefit most from such a therapy (i.e., the elderly, postmenopausal women, etc.) in hopes of eliciting multidisciplinary scientific inquiries into this potentially therapeutic aid which presumably has global ramifications.

Nutritional biochemistry of spaceflight

As we approach the end of the first 50 years of human space travel, much has been learned about adaptation to microgravity and the risks associated with extended-duration space exploration. As the frequency and duration of flights grew, nutrition issues became more critical and the questions to be answered became more complex: What are the nutrient requirements for space travelers? Can nutrients be used as tools to mitigate the negative effects of space travel on humans? How does nutrition interrelate with other physiological systems (such as muscle, bone, and cardiovascular system) and their adaptation to microgravity? Much research has been done over the decades in both actual spaceflight and ground-based analogs. We review here much of what is known, and highlight areas of ongoing research and concerns for future exploration of the Moon, Mars, and beyond.

Arterial stiffness acutely decreases after whole-body vibration in humans

BACKGROUND

Increased arterial stiffness is a well-established cardiovascular risk factor. Mechanical stimuli to artery, such as compression, elicit vasodilation and acutely decrease arterial stiffness. As whole-body vibration (WBV)-induced oscillation is propagated at least to lumbar spine, WBV mechanically stimulates abdominal and leg arteries and may decrease arterial stiffness. WBV is feasible in vulnerable and immobilized humans. Therefore, it is worthwhile to explore the possibility of WBV as a valuable adjunct to exercise training.

AIM

The aim of this study was to investigate the acute effects of WBV on arterial stiffness.

METHODS

Ten healthy men performed WBV and control (CON) trials on separate days. The WBV session consisted of 10 sets of vibration (frequency, 26 Hz) for 60 s with an inter-set rest period of 60 s. Subjects maintained a static squat position with knees bent on a platform. In the CON trial, WBV stimulation was not imposed. Blood pressure, heart rate and brachial-ankle pulse wave velocity (baPWV), an index of arterial stiffness, were measured before and 20, 40 and 60 min after both trials.

RESULTS AND CONCLUSION

Heart rate and blood pressure did not change from baseline after both trials. Although baPWV did not change in the CON trial (baseline vs. after 20, 40 and 60 min; 1144 +/- 35 vs. 1164 +/- 41, 1142 +/- 39, and 1148 +/- 34 cm s(-1)), baPWV decreased 20 and 40 min after the WBV trial and recovered to baseline 60 min after the trial (1137 +/- 28 vs. 1107 +/- 30, 1108 +/- 28, and 1128 +/- 25 cm s(-1)). These results suggest that WBV acutely decreases arterial stiffness.

Whole-body vibration slows the acquisition of fat in mature female rats

OBJECTIVE

To evaluate the effects of whole-body vibration on fat, bone, leptin and muscle mass.

METHODS/DESIGN

Thirty 7-month-old female 344 Fischer rats were randomized by weight into three groups (baseline, vibration or control; n=8-10 per group). Rats in the vibration group were placed inside individual compartments attached to a Pneu-Vibe vibration platform (Pneumex, Sandpoint, ID, USA) and vibrated at 30-50 Hz (6 mm peak to peak) for 30 min per day, 5 days per week, for 12 weeks. The vibration intervention consisted of six 5-min cycles with a 1-min break between cycles.

RESULTS

There were significant body composition differences between the whole-body vibration and the control group. The whole-body vibration group weighed approximately 10% less (mean+/-s.d.; 207+/-10 vs 222+/-15 g, P<0.03) and had less body fat (20.8+/-3.8 vs 26.8+/-5.9 g, P<0.05), a lower percentage of body fat (10.2+/-1.7 vs 12+/-2.0%, P<0.05), and lower serum leptin levels (1.06+/-0.45 vs 2.27+/-0.57 ng ml(-1), P<0.01) than the age-matched controls. No differences were observed for total lean mass, bone mineral content (BMC), bone mineral density (BMD), insulin-like growth factor-I (IGF-I) or soleus (SOL) and extensor digitorum longus (EDL) mass or function. Regional high-resolution dual-energy X-ray absoptiometry scans of the lumbar spine (L1-4) revealed that the whole-body vibration group had significantly greater BMC (0.33+/-0.05 vs 0.26+/-0.03 g, P<0.01) and BMD (0.21+/-0.01 vs 0.19+/-0.01 g cm(-2), P<0.01) than the control group. No differences between the groups were observed in the amount of food consumed.

CONCLUSION

These findings show that whole-body vibration reduced body fat accumulation and serum leptin without affecting whole body BMC, BMD or lean mass. However, the increase in vertebral BMC and BMD suggests that vibration may have resulted in local increases in bone mass and density. Also, whole-body vibration did not affect muscle function or food consumption.

Transmission of vertical whole body vibration to the human body

According to experimental studies, low-amplitude high-frequency vibration is anabolic to bone tissue, whereas in clinical trials, the bone effects have varied. Given the potential of whole body vibration in bone training, this study aimed at exploring the transmission of vertical sinusoidal vibration to the human body over a wide range of applicable amplitudes (from 0.05 to 3 mm) and frequencies (from 10 to 90 Hz). Vibration-induced accelerations were assessed with skin-mounted triaxial accelerometers at the ankle, knee, hip, and lumbar spine in four males standing on a high-performance vibration platform. Peak vertical accelerations of the platform covered a range from 0.04 to 19 in units of G (Earth's gravitational constant). Substantial amplification of peak acceleration could occur between 10 and 40 Hz for the ankle, 10 and 25 Hz for the knee, 10 and 20 Hz for the hip, and at 10 Hz for the spine. Beyond these frequencies, the transmitted vibration power declined to 1/10th-1/1000 th of the power delivered by the platform. Transmission of vibration to the body is a complicated phenomenon because of nonlinearities in the human musculoskeletal system. These results may assist in estimating how the transmission of vibration-induced accelerations to body segments is modified by amplitude and frequency and how well the sinusoidal waveform is maintained. Although the attenuation of vertical vibration at higher frequencies is fortunate from the aspect of safety, amplitudes >0.5 mm may result in greater peak accelerations than imposed at the platform and thus pose a potential hazard for the fragile musculoskeletal system.

Constrained tibial vibration in mice: a method for studying the effects of vibrational loading of bone

Vibrational loading can stimulate the formation of new trabecular bone or maintain bone mass. Studies investigating vibrational loading have often used whole-body vibration (WBV) as their loading method. However, WBV has limitations in small animal studies because transmissibility of vibration is dependent on posture. In this study, we propose constrained tibial vibration (CTV) as an experimental method for vibrational loading of mice under controlled conditions. In CTV, the lower leg of an anesthetized mouse is subjected to vertical vibrational loading while supporting a mass. The setup approximates a one degree-of-freedom vibrational system. Accelerometers were used to measure transmissibility of vibration through the lower leg in CTV at frequencies from 20 Hz to 150 Hz. First, the frequency response of transmissibility was quantified in vivo, and dissections were performed to remove one component of the mouse leg (the knee joint, foot, or soft tissue) to investigate the contribution of each component to the frequency response of the intact leg. Next, a finite element (FE) model of a mouse tibia-fibula was used to estimate the deformation of the bone during CTV. Finally, strain gages were used to determine the dependence of bone strain on loading frequency. The in vivo mouse leg in the CTV system had a resonant frequency of 60 Hz for +/-0.5 G vibration (1.0 G peak to peak). Removing the foot caused the natural frequency of the system to shift from 60 Hz to 70 Hz, removing the soft tissue caused no change in natural frequency, and removing the knee changed the natural frequency from 60 Hz to 90 Hz. By using the FE model, maximum tensile and compressive strains during CTV were estimated to be on the cranial-medial and caudolateral surfaces of the tibia, respectively, and the peak transmissibility and peak cortical strain occurred at the same frequency. Strain gage data confirmed the relationship between peak transmissibility and peak bone strain indicated by the FE model, and showed that the maximum cyclic tibial strain during CTV of the intact leg was 330+/-82microepsilon and occurred at 60-70 Hz. This study presents a comprehensive mechanical analysis of CTV, a loading method for studying vibrational loading under controlled conditions. This model will be used in future in vivo studies and will potentially become an important tool for understanding the response of bone to vibrational loading.

Occupational physical activities and long-term functional and radiographic outcomes in patients with ankylosing spondylitis

OBJECTIVE

We sought to identify specific occupational activities associated with functional limitations and radiographic damage in patients with longstanding ankylosing spondylitis (AS).

METHODS

We asked patients diagnosed with AS for >or=20 years to report all past occupations, which we mapped to specific physical activities using the Occupational Information Network, which is the US Department of Labor job classification database. For each occupation reported, we obtained ratings for 13 physical abilities of the worker and 13 aspects of the work environment or work tasks (work context) thought to be most relevant to patients with AS. Averages for each measure, weighted by the number of years in each job, were related to the degree of functional limitation as assessed by the Bath AS Functional Index (BASFI) and to the extent of spinal radiographic damage as assessed by the Bath AS Radiology Index for the spine (BASRI-s).

RESULTS

Among 397 patients, those with a history of jobs requiring dynamic flexibility (the ability to repeatedly bend, stretch, twist, or reach) had more functional limitations than those whose past jobs required little or no dynamic flexibility (adjusted mean BASFI score 48.3 in the top quartile versus 38.1 in all others). Those whose past jobs required more dynamic flexibility, extent flexibility, and exposure to whole body vibration also had significantly higher BASRI-s scores.

CONCLUSION

Bending, twisting, and stretching are the occupational activities associated with greater functional limitations and radiographic damage in patients with longstanding AS. Exposure to whole body vibration was also associated with more radiographic damage.

A comparison of the physiologic effects of acute whole-body vibration exercise in young and older people

OBJECTIVE

To examine the acute physiologic effects of acute whole-body vibration (WBV) exercise in young and older people.

DESIGN

Every participant performed 9 conditions in a static squat position, consisting of no vibration and WBV at 30Hz and 3 loads corresponding to (1) no load (0% body mass), (2) load of 20% body mass, and (3) load of 40% body mass. A Jendrassik voluntary contraction was also performed with no vibration and WBV at 30Hz with no load and 20% body mass.

SETTING

Laboratory facilities at a university in the United Kingdom.

PARTICIPANTS

Healthy young people (n=12; 6 men, 6 women; mean age, 21.5y) and 12 healthy older people (6 men, 6 women; mean age, 69.2y) from the local community.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

The Physical Activity Questionnaire, anthropometric measures, counter-movement jump, and isometric maximal voluntary contraction with the Jendrassik maneuver were assessed in both groups. Oxygen uptake (Vo2), blood pressure, heart rate, and rating of perceived exertion (RPE) were recorded during WBV and load conditions as the outcome of the study.

RESULTS

Both vibration and load were associated with an increase (P<.001) in Vo2 for older and young groups. WBV elicited the equivalent of a .35 metabolic equivalent (MET) increase in Vo2, with additional loads of 20% and 40% body mass increasing Vo2 by 0.8 and 1.2 METs, respectively. Additionally, there was an interaction effect of vibration and group in which the WBV-related Vo2 increase was less in the old compared with the young. Both vibration and load caused an increase in heart rate, blood pressure, and RPE (all P<.001); however, there were no significant group differences between young and older groups. The Jendrassik maneuver elicited an increase in Vo2 by 27.6% for the old and 33% for the young group (P<.001); however, there was no significant difference between groups.

CONCLUSIONS

Vo2 significantly increased in both the older and young people with vibration and additional load and when the Jendrassik maneuver was superimposed with vibration and load. However, the elicited increase in Vo2 (1.2mL x kg(-1).min(-1)) from WBV may be an insufficient stimulus to improve cardiovascular fitness.

Relevance of motion artifact in electromyography recordings during vibration treatment

Electromyography readings (EMGs) from quadriceps of fifteen subjects were recorded during whole body vibration treatment at different frequencies (10-50 Hz). Additional electrodes were placed on the patella to monitor the occurrence of motion artifact, triaxial accelerometers were placed onto quadriceps to monitor motion. Signal spectra revealed sharp peaks corresponding to vibration frequency and its harmonics, in accordance with the accelerometer data. EMG total power was compared to that associated with vibration harmonics narrow bands, before and during vibration. On average, vibration associated power resulted in only 3% (+/-0.9%) of the total power prior to vibration and 29% (+/-13.4%) during vibration. Often, studies employ surface EMG to quantitatively evaluate vibration evoked muscular activity and to set stimulation frequency. However, previous research has not accounted for motion artifacts. The data presented in this study emphasize the need for the removal of motion artifacts, as they consistently affect RMS estimation, which is often used as a concise muscle activity index during vibrations. Such artifacts, rather unpredictable in amplitude, might be the cause of large inter-study differences and must be eliminated before analysis. Motion artifact filtering will contribute to thorough and precise interpretation of neuromuscular response to vibration treatment.

Vibration safety limits for magnetic resonance elastography

Magnetic resonance elastography (MRE) has been demonstrated to have potential as a clinical tool for assessing the stiffness of tissue in vivo. An essential step in MRE is the generation of acoustic mechanical waves within a tissue via a coupled mechanical driver. Motivated by an increasing volume of human imaging trials using MRE, the objectives of this study were to audit the vibration amplitude of exposure for our IRB-approved human MRE studies, to compare these values to a conservative regulatory standard for vibrational exposure and to evaluate the applicability and implications of this standard for MRE. MRE displacement data were examined from 29 MRE exams, including the liver, brain, kidney, breast and skeletal muscle. Vibrational acceleration limits from a European Union directive limiting occupational exposure to whole-body and extremity vibrations (EU 2002/44/EC) were adjusted for time and frequency of exposure, converted to maximum displacement values and compared to the measured in vivo displacements. The results indicate that the vibrational amplitudes used in MRE studies are below the EU whole-body vibration limit, and the EU guidelines represent a useful standard that could be readily accepted by Institutional Review Boards to define standards for vibrational exposures for MRE studies in humans.

Nonpharmacologic management of osteoporosis to minimize fracture risk

The traditional management of osteoporosis has focused on the pharmacologic aspects of treatment. Nonpharmacologic approaches, such as the use of orthoses, exercise programs, calcium and vitamin D supplementation, fall prevention, and kyphoplasty have largely been overlooked. Evidence for an essential contribution of nonpharmacologic treatments in the management of osteoporotic patients is increasing, particularly for patients who cannot, or will not, comply with medication regimens. This Review highlights the most important aspects of nonpharmacologic management of osteoporosis.

Frequency-dependent enhancement of bone formation in murine tibiae and femora with knee loading

Knee loading is a relatively new loading modality in which dynamic loads are laterally applied to the knee to induce bone formation in the tibia and the femur. The specific aim of the current study was to evaluate the effects of loading frequencies (in Hz) on bone formation at the site away from the loading site on the knee. The left knee of C57/BL/6 mice was loaded with 0.5 N force at 5, 10, or 15 Hz for 3 min/day for 3 consecutive days, and bone histomorphometry was conducted at the site 75% away from the loading site along the length of tibiae and femora. The results revealed frequency-dependent induction of bone formation, in which the dependence was different in the tibia and the femur. Compared with the sham-loading control, for instance, the cross-sectional cortical area was elevated maximally at 5 Hz in the tibia, whereas the most significant increase was observed at 15 Hz in the femur. Furthermore, mineralizing surface, mineral apposition rate, and bone formation rate were the highest at 5 Hz in the tibia (2.0-, 1.4-, and 2.7 fold, respectively) and 15 Hz in the femur (1.5-, 1.2-, and 1.8 fold, respectively). We observed that the tibia had a lower bone mineral density with more porous microstructures than the femur. Those differences may contribute to the observed differential dependence on loading frequencies.

Walking intensity for postmenopausal bone mineral preservation and accrual

INTRODUCTION

Mechanical stresses on the bone are an important aspect of physical activity that promotes bone preservation and increases in bone mass. Exercise intensities leading to bone preservation and accrual have not been adequately defined for humans in general, and postmenopausal women in particular.

MATERIALS AND METHODS

To quantify parameters of effective walking intensity for preservation and accrual of bone mineral, healthy postmenopausal women engaged in 30 weeks of supervised walking, 4.8 km per day, 4 days a week at intensities of 102% or 123% of the ventilatory threshold (VT) equivalent to 67% and 86% of maximal effort (VO2 max). Subjects were matched by age, body mass, hormone replacement status (HRT) and VT. Areal bone mineral density (aBMD) determined by DXA (n=25) and bone formation markers osteocalcin (OC), and bone-specific alkaline phosphatase (bALP) (n=43), were measured at the outset and at 15-week intervals. Peak vertical forces at corresponding intensities were measured (n=9) on a force plate.

RESULTS

aBMD of legs and whole body, but not of other sites, and lean mass of legs, but not of arms, increased after 15 weeks of high intensity, compared to moderate losses for low intensity training. Leg and total body aBMD was preserved and slightly increased with loads greater than 872.3 newtons (N) with a walking intensity above 115% of VT or 74% of VO2 max, speeds above 6.14 km/h, and heart rates above 82.3% of age-specific maximum. OC and bALP did not correlate with training-induced changes in aBMD.

CONCLUSIONS

At exercise intensities above 115% of VT or 74% of VO2 max, and walking speeds above 6.14 km/h, mechanical loading of 872.3 N or 1.22 times body weight is sufficient for increases in leg muscle mass and preservation of BMD in postmenopausal women.

Advances in the medical management of osteoporosis

Osteoporosis is a skeletal disorder characterised by compromised bone strength predisposing to increased risk of fracture, which is rapidly reaching epidemic proportions as the population ages. Many patients presenting with a fracture caused by a fall from standing height or less are not on any kind of therapy and many patients who sustain these fragility fractures are not started on therapy by their orthopaedic surgeon. In 2004, the United States Surgeon General released a report on osteoporosis recommending that physicians adopt a pyramidal approach to therapy. The base of the pyramid includes calcium, vitamin D, physical therapy and fall prevention. The second level calls for management or elimination of secondary causes of osteoporosis. The third level consists of treatment with either anti-resorptive or anabolic medications. The orthopaedic surgeon is in an ideal position to diagnose fragility fractures and suggest treatment in the hope of preventing future fractures. Anti-resorptive and anabolic therapies currently available are discussed.

Small oscillatory accelerations, independent of matrix deformations, increase osteoblast activity and enhance bone morphology

A range of tissues have the capacity to adapt to mechanical challenges, an attribute presumed to be regulated through deformation of the cell and/or surrounding matrix. In contrast, it is shown here that extremely small oscillatory accelerations, applied as unconstrained motion and inducing negligible deformation, serve as an anabolic stimulus to osteoblasts in vivo. Habitual background loading was removed from the tibiae of 18 female adult mice by hindlimb-unloading. For 20 min/d, 5 d/wk, the left tibia of each mouse was subjected to oscillatory 0.6 g accelerations at 45 Hz while the right tibia served as control. Sham-loaded (n = 9) and normal age-matched control (n = 18) mice provided additional comparisons. Oscillatory accelerations, applied in the absence of weight bearing, resulted in 70% greater bone formation rates in the trabeculae of the metaphysis, but similar levels of bone resorption, when compared to contralateral controls. Quantity and quality of trabecular bone also improved as a result of the acceleration stimulus, as evidenced by a significantly greater bone volume fraction (17%) and connectivity density (33%), and significantly smaller trabecular spacing (-6%) and structural model index (-11%). These in vivo data indicate that mechanosensory elements of resident bone cell populations can perceive and respond to acceleratory signals, and point to an efficient means of introducing intense physical signals into a biologic system without putting the matrix at risk of overloading. In retrospect, acceleration, as opposed to direct mechanical distortion, represents a more generic and safe, and perhaps more fundamental means of transducing physical challenges to the cells and tissues of an organism.

High-Frequency Whole-Body Vibration Improves Balancing Ability in Elderly Women

OBJECTIVE

To investigate the efficacy of high-frequency whole-body vibration (WBV) on balancing ability in elderly women.

DESIGN

Randomized controlled trial. Subjects were randomized to either the WBV intervention or the no-treatment control group.

SETTING

Community-living elderly women.

PARTICIPANTS

Sixty-nine elderly women aged 60 or above without habitual exercise.

INTERVENTION

Side alternating WBV at 20Hz with 3 minutes a day and 3 days a week for 3 months in the WBV intervention group. Those in control group remained sedentary with normal daily life for the whole study period.

MAIN OUTCOME MEASURES

Limits of stability in terms of reaction time, movement velocity, directional control, endpoint excursion, maximum excursion, and the functional reach test were performed at baseline and endpoint.

RESULTS

Significant enhancement of stability was detected in movement velocity (P<.01), maximum point excursion (P<.01), in directional control (P<.05).

CONCLUSIONS

WBV was effective in improving the balancing ability in elderly women. This also provides evidence to support our user-friendly WBV treatment protocol of 3 minutes a day for the elderly to maintain their balancing ability and reduce risks of fall.

Low-level accelerations applied in the absence of weight bearing can enhance trabecular bone formation

High-frequency whole body vibrations can be osteogenic, but their efficacy appears limited to skeletal segments that are weight bearing and thus subject to the induced load. To determine the anabolic component of this signal, we investigated whether low-level oscillatory displacements, in the absence of weight bearing, are anabolic to skeletal tissue. A loading apparatus, developed to shake specific segments of the murine skeleton without the direct application of deformations to the tissue, was used to subject the left tibia of eight anesthesized adult female C57BL/6J mice to small (0.3 g or 0.6 g) 45 Hz sinusoidal accelerations for 10 min/day, while the right tibia served as an internal control. Video and strain analysis revealed that motions of the apparatus and tibia were well coupled, inducing dynamic cortical deformations of less than three microstrain. After 3 weeks, trabecular metaphyseal bone formation rates and the percentage of mineralizing surfaces (MS/BS) were 88% and 64% greater (p < 0.05) in tibiae accelerated at 0.3 g than in their contralateral controls. At 0.6 g, bone formation rates and mineral apposition rates were 66% and 22% greater (p < 0.05) in accelerated tibiae. Changes in bone morphology were evident only in the epiphysis, where stimulated tibiae displayed significantly greater cortical area (+8%) and thickness (+8%). These results suggest that tiny acceleratory motions--independent of direct loading of the matrix--can influence bone formation and bone morphology. If confirmed by clinical studies, the unique nature of the signal may ultimately facilitate the stimulation of skeletal regions that are prone to osteoporosis even in patients that are suffering from confinement to wheelchairs, bed rest, or space travel.

Modeling the mechanical consequences of vibratory loading in the vertebral body: microscale effects

Osteoporosis affects nearly 10 million individuals in the United States. Conventional treatments include anti-resorptive drug therapies, but recently, it has been demonstrated that delivering a low magnitude, dynamic stimulus via whole body vibration can have an osteogenic effect without the need for large magnitude strain stimulus. Vibration of the vertebral body induces a range of stimuli that may account for the anabolic response including low magnitude strains, interfacial shear stress due to marrow movement, and blood transport. In order to evaluate the relative importance of these stimuli, we integrated a microstructural model of vertebral cancellous bone with a mixture theory model of the vertebral body. The predicted shear stresses on the surfaces of the trabeculae during vibratory loading are in the range of values considered to be stimulatory and increase with increasing solid volume fraction. Peak volumetric blood flow rates also varied with strain amplitude and frequency, but exhibited little dependence on solid volume fraction. These results suggest that fluid shear stress governs the response of the vertebrae to whole body vibration and that the marrow viscosity is a critical parameter which modulates the shear stress.

Osteoporosis: pathogenesis, new therapies and surgical implications

Many developments occurred in the realm of bone healing in recent years. Genetic discoveries, new proteins affecting bone health, and new treatments have steered our treatment of traumatic and iatrogenic fractures in new directions. Osteoporosis strikes many subsets of the world population, including: women, the elderly, and those suffering from arthritis, autoimmune diseases, HIV, and the immunocompromised. This disease predisposes people to an increased risk of low trauma and fragility fractures. The baby boomer generation and an increasing lifespan may burden the economy by creating such a large group susceptible to such a potentially devastating disease. The novel treatments and coping with the potentially challenging surgical implications will aide the podiatric physician in both medical and surgical management of osteoporosis.

Whole-body vibration can reduce calciuria induced by high protein intakes and may counteract bone resorption: A preliminary study

Excess protein intake can adversely affect the bone via an increase in calcium excretion, while suitable mechanical loading promotes osteogenesis. We therefore investigated whether vibration exposure could alleviate the bone mineral losses associated with a metabolic acidosis. Ten healthy individuals aged 22 - 29 years (median = 25) underwent three 5-day study periods while monitoring their dietary intake. The study consisted of recording the participants' usual dietary intake for 5 consecutive days. Participants were then randomly divided into two groups, one of which received a protein supplement (2 g x kg(-1) body mass x day(-1); n = 5) and the other whole-body low-magnitude (3.5 g), low-frequency (30 Hz) mechanical vibration (WBV) delivered through a specially designed vibrating plate for 10 min each day (n = 5). Finally, for the third treatment period, all participants consumed the protein supplement added to their normal diet and were exposed to WBV exercise for 10 min per day. Daily urine samples were collected throughout the experimental periods to determine the excretion of calcium, phosphate, titratable acid, urea, and C-telopeptide. As expected, when the participants underwent the high protein intake, there was an increase in urinary excretion rates of calcium (P < 0.001), phosphate (P < 0.003), urea (P < 0.001), titratable acid (P < 0.001), and C-telopeptide (P < 0.05) compared with baseline values. However, high protein intake coupled with vibration stimulation resulted in a significant reduction in urinary calcium (P = 0.006), phosphate excretion (P = 0.021), and C-telopeptide (P < 0.05) compared with protein intake alone, but did not affect titratable acid and urea output. The participants showed no effect of WBV exercise alone on urinary excretion of calcium, phosphate, urea, titratable acid, or C-telopeptide. The results indicate that vibration stimulation can moderate the increase in bone resorption and reduction in bone formation caused by a metabolic acidosis.

Relationship of bone health to yearlong physical activity in older Japanese adults: cross-sectional data from the Nakanojo Study

INTRODUCTION

We determined associations between bone health and the quantity and quality of habitual physical activity in a cohort of 172 free-living Japanese aged 65-83 years (76 men, 96 women).

METHODS

The number of steps taken and the intensity of physical activity were measured every 4 s throughout each 24-h period for 1 year, using a specially adapted accelerometer that distinguished up to 11 levels of physical activity (expressed in metabolic equivalents, METs). At the end of the year, a quantitative ultrasonic technique assessed each participant's osteosonic index (OSI, reflecting bone stiffness in the calcaneus).

RESULTS

The data were significantly described by linear and exponential regression models which showed that in both sexes the OSI score increased with increasing daily physical activity, up to the observed maximum values of approximately 14,000 steps/day and 50 min/day at an intensity >3 METs. However, when data were categorized into quartiles of physical activity, OSI scores were not significantly greater in persons exceeding recommended minimum standards of habitual physical activity (corresponding to counts of around 6,900 and 6,800 steps/day and durations >3 METs of around 18 and 16 min/day in men and women, respectively). All who met such criteria (with the exception of a few women) had OSI scores above the threshold for a clinical diagnosis of osteoporosis. Multivariate-adjusted logistic regression analyses predicted that men and especially women who engaged in <6,800 steps/day and <16 min/day of moderate-intensity physical activity were, respectively, 4.9-8.4 and 2.2-3.5 times more likely to sustain fractures than those participating in >8,200 steps/day and >25 min/day of activity >3 METs.

CONCLUSION

Causation cannot be inferred from a cross-sectional study. Nevertheless, we suggest that from the viewpoint of bone health, elderly people should be encouraged to engage in low- and moderate-intensity habitual physical activity, taking >7,000 steps/day with a duration >15 min/day at >3 METs.

Intraskeletal variability in bone mass

For methodological or other reasons, a variety of skeletal elements are analyzed and subsequently used as a basis for describing general bone loss and mass. However, bone loss and mass may not be uniform within and among skeletal elements of the same individual because of biomechanical factors. We test the hypothesis that a homogeneity in bone mass exists among skeletal elements of the same individual. Measures indicative of bone mass were calculated from the midshafts of six skeletal elements from the same individuals (N = 41). The extent of intraskeletal variability in bone mass (relative cortical area) was then examined for the entire sample, according to age, sex, and pathological status. The results of the analysis showed that all measures reflect a heterogeneity in bone mass (P </= 0.001). Specifically, differences were observed between the bones of the upper limb and those of the lower limb. Both sexes showed intraskeletal variability in bone mass, but the difference between the sexes is not significant (P = 0.509). When the sample is subdivided according to age, all groups show intraskeletal variability in bone mass, but the difference did not differ significantly among the groups (P = 0.217). However, significant differences in intraskeletal variability are observed between individuals below and above the age of 50. Pathological individuals show intraskeletal variability in bone mass, but the difference between the pathological and non-pathological groups is not significant (P = 0.095). These results indicate that the bone mass of any particular skeletal element is intricately tethered to its specific mechanical loading environment.

Exercise for people with osteoporosis: translating the science into clinical practice

The "holy grail" of inquiry regarding exercise and osteoporosis has been identifying a type of exercise that builds bone. Investigation using animal models has provided many insights into how bone responds to mechanical loading, but translating these findings into an exercise prescription for patients with osteoporosis is difficult. Patients expect bone to respond to exercise in a linear fashion, such as they are accustomed to experiencing with muscles in response to progressive strength training or with the cardiopulmonary system in response to endurance training. If the skeleton accrued greater mass in response to increasing intensity and duration of mechanical strain, our bones would weigh so much that we could not move. A unique requirement of bone is that adaptations to loading produce the strongest and the lightest structure. More exercise is not always better, but we are not yet sure exactly what and how much is enough and what and how much is too much. This complexity stymies clear communication, both in the clinic and in public health initiatives.

The acute effects of different whole body vibration amplitudes on the endocrine system of young healthy men: a preliminary study

Whole body vibration (WBV) has been suggested as an alternative form of exercise producing adaptive responses similar to that of resistance training. Very limited information is available on the effects of different vibration parameters on anabolic hormones. In this study, we compared the acute effects of different WBV amplitudes on serum testosterone (T) and insulin growth factor-1 (IGF-1). Nine healthy young recreationally active adult males (age 22 +/- 2 years, height 181 +/- 6.3 cm, weight 77.4 +/- 9.5 kg) voluntarily participated in this randomized controlled (cross-over design) study. The subjects performed 20 sets of 1 min each of WBV exercise in the following conditions: Non-vibration condition (control), low amplitude vibration [low (30 Hz, 1.5 mm peak-to-peak amplitude)] and high amplitude vibration [high (30 Hz, 3 mm peak-to-peak amplitude)]. Blood samples were collected before, after 10 sets, at the end (20th set) and after 24 h of the exercise bout. WBV exercise did not produce significant changes in serum T and IGF-1 either with low or high amplitude when compared with the control condition. The results of this study demonstrate that a single session of WBV exposure with a frequency of 30 Hz and amplitudes of 1.5 and 3 mm does not noticeably alter serum T and IGF-1 levels.

Low-amplitude, broad-frequency vibration effects on cortical bone formation in mice

Mechanical loading of the skeleton is necessary to maintain bone structure and strength. Large amplitude strains associated with vigorous activity typically result in the greatest osteogenic response; however, data suggest that low-amplitude, broad-frequency vibration results in new bone formation and may enhance adaptation through a stochastic resonance (SR) phenomenon. That is, random noise may maximally enhance bone formation to a known osteogenic stimulus. The aims of this study were to (1) assess the ability of different vibration signals to enhance cortical bone formation during short- and long-term loading and (2) determine whether vibration could effect SR in bone. Two studies were completed wherein several osteogenic loading waveforms, with or without an additive low-amplitude, broad-frequency (0-50 Hz) vibration signal, were applied to the mouse ulna in axial compression. In study 1, mice were loaded short-term (30 s/day, 2 days) with either a carrier signal alone (1 or 2 N sine waveform), vibration signal alone [0.1 N or 0.3 N root mean square (RMS)] or combined carrier and vibration signal. In study 2, mice were loaded long-term (30 s/day, 3 days/week, 4 weeks) with a carrier signal alone (static or sine waveform), vibration signal alone (0.02 N, 0.04 N, 0.08 N or 0.25 N RMS) or combined carrier and vibration signal. Sequential calcein bone labels were administered at 2 and 4 days and at 4 and 29 days after the first day of loading in study 1 and 2, respectively; bone formation parameters and changes in geometry were measured. Combined application of the carrier and vibration signals in study 1 resulted in significantly greater bone formation than with either signal alone (P < 0.001); however, this increase was independently explained by increased strain levels associated with additive vibration. When load and strain levels were similar across loading groups in study 2, cortical bone formation and changes in geometry were not significantly altered by vibration. Vibration alone did not result in any new bone formation. Our data suggest that low-amplitude, broad-frequency vibration superimposed onto an osteogenic waveform or vibration alone does not enhance cortical bone adaptation at the frequencies, amplitudes and loading periods tested.

Low-level mechanical vibrations can influence bone resorption and bone formation in the growing skeleton

Short durations of extremely small magnitude, high-frequency, mechanical stimuli can promote anabolic activity in the adult skeleton. Here, it is determined if such signals can influence trabecular and cortical formative and resorptive activity in the growing skeleton, if the newly formed bone is of high quality, and if the insertion of rest periods during the loading phase would enhance the efficacy of the mechanical regimen. Eight-week-old female BALB/cByJ mice were divided into four groups, baseline control (n = 8), age-matched control (n = 10), whole-body vibration (WBV) at 45 Hz (0.3 g) for 15 min day(-1) (n = 10), and WBV that were interrupted every second by 10 of rest (WBV-R, n = 10). In vivo strain gaging of two additional mice indicated that the mechanical signal induced strain oscillations of approximately 10 microstrain on the periosteal surface of the proximal tibia. After 3 weeks of WBV, applied for 15 min each day, osteoclastic activity in the trabecular metaphysis and epiphysis of the tibia was 33% and 31% lower (P <0.05) than in age-matched controls. Bone formation rates (BFR.BS(-1)) on the endocortical surface of the metaphysis were 30% greater (P <0.05) in WBV than in age-matched control mice but trabecular and middiaphyseal BFR were not significantly altered. The insertion of rest periods (WBV-R) failed to potentiate the cellular effects. Three weeks of either WBV or WBV-R did not negatively influence body mass, bone length, or chemical bone matrix properties of the tibia. These data indicate that in the growing skeleton, short daily periods of extremely small, high-frequency mechanical signals can inhibit trabecular bone resorption, site specifically attenuate the declining levels of bone formation, and maintain a high level of matrix quality. If WBV prove to be efficacious in the growing human skeleton, they may be able to provide the basis for a non-pharmacological and safe means to increase peak bone mass and, ultimately, reduce the incidence of osteoporosis or stress fractures later in life.

Knee loading stimulates cortical bone formation in murine femurs

Background

Bone alters its architecture and mass in response to the mechanical environment, and thus varying loading modalities have been examined for studying load-driven bone formation. The current study aimed to evaluate the anabolic effects of knee loading on diaphyseal cortical bone in the femur.

Methods

Using a custom-made piezoelectric loader, 0.5-N loads were laterally applied to the left knee of C57/BL/6 mice at 5, 10, 15, and 20 Hz for 3 minutes per day for 3 consecutive days. Animals were sacrificed for examination 13 days after the last loading. The contralateral femur was used as a non-loading control, and the statistical significance of loading effects was evaluated with p < 0.05.

Results

Although diaphyseal strains were measured as small as 12 μstrains, bone histomorphometry clearly demonstrated frequency-dependent enhancement of bone formation. Compared to a non-loading control, bone formation on the periosteal surface was significantly enhanced. The loading at 15 Hz was most effective in elevating the mineralizing surface (1.7 x; p < 0.05), mineral apposition rate (1.4 x; p < 0.001), and bone formation rate (2.4 x; p < 0.01). The loading at 10 Hz elevated the mineralizing surface (1.4 x; p < 0.05), mineral apposition rate (1.3 x; p < 0.01), and bone formation rate (1.8 x; p < 0.05). The cross-sectional cortical area and the cortical thickness in the femoral diaphysis were significantly increased by loading at 10 Hz (both 9%) and 15 Hz (12% and 13%, respectively).

Conclusion

The results support the anabolic effects of knee loading on diaphyseal cortical bone in the femur with small in situ strain, and they extend our knowledge on the interplay between bone and joints. Strengthening the femur contributes to preventing femoral fractures, and the discovery about the described knee loading might provide a novel strategy to strengthen osteoporotic bones. Further analyses are required to understand the biophysical and molecular mechanism behind knee loading.

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

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.

Low-magnitude mechanical signals that stimulate bone formation in the ovariectomized rat are dependent on the applied frequency but not on the strain magnitude

There is growing evidence that extremely small mechanical signals, if applied at a sufficiently high frequency, can serve as anabolic signals to bone tissue. To determine if the responsiveness of bone to low-magnitude, high-frequency parameters is modulated by endocrine imbalance, ovariectomized (OVX) Sprague-Dawley rats were subjected to whole body vibrations (WBV, 0.15 g) at 45 Hz (n=6) or 90 Hz (n=6) for 10 min/day, and compared to OVX age-matched controls (n=6). Five additional rats were used, in vivo, to establish the induced bone surface strain magnitudes (and strain rates). Following a 28 d protocol, bone formation rates in the metaphysis of the proximal tibia were 159% greater in 90 Hz rats when compared to age-matched controls, but 45 Hz rats were not significantly different from controls. Bone morphology of 90 Hz rats indicated significantly greater trabecular bone volume (22% and 25%) and thicker trabeculae (11% and 12%) over either controls or 45 Hz rats in the epiphysis of the distal femur, respectively. Despite the enhanced sensitivity of the skeleton towards the 90 Hz signal, the strain magnitudes and strain rates induced by this frequency were significantly lower than during 45 Hz vibration, suggesting that factors other than matrix strain are driving the anabolic response. Ideally, such mechanical signals represent a non-pharmacologic means of controlling bone mass and morphology in spite of systemic pressures for bone resorption.

The Effect of Varying Magnitudes of Whole-Body Vibration on Several Skeletal Sites in Mice

It has been reported that whole-body vibration (WBV) is anabolic to trabecular bone in animal models and humans. It is likely that this anabolic response does not occur uniformly throughout the entire body. Two factors that may affect the observed anabolic response are vibration magnitude and skeletal site of interest. In this study, mice were loaded with WBV of varying magnitudes. After five weeks of loading, bone marrow was flushed from tibias in order to quantify osteoprogenitor cells. Staining with alizarin red (an indicator of mineralization) showed a significant decrease in percent stained area in the 0.3 g loaded group compared to the control group and the 1.0 g group. MicroCT analysis was performed at five skeletal sites: the proximal tibial metaphysis, femoral condyles, distal femoral metaphysis, proximal femur, and L5 vertebral body. Increasing magnitudes of WBV were associated with a non-dose-dependent increase in trabecular bone volume (BV/TV) at the proximal tibial metaphysis, although other sites were unresponsive. There were statistically significant increases in BV/TV in the 0.1 g group (32% increase) and 1.0 g group (43% increase) compared to control (p < 0.05). The 0.1 g and 1.0 g groups also had higher BV/TV than the 0.3 g loaded group. If this non-dose-dependent phenomenon is verified by future studies, it suggests that a range of magnitudes should be examined for each application of WBV.

Management of osteoporosis in postmenopausal women

OBJECTIVE

To update the evidence-based position statement published by The North American Menopause Society (NAMS) in 2002 regarding the management of osteoporosis in postmenopausal women.

DESIGN

NAMS followed the general principles established for evidence-based guidelines to create this updated document. A panel of clinicians and researchers expert in the field of metabolic bone diseases and/or women's health were enlisted to review the 2002 NAMS position statement, compile supporting statements, and reach consensus on recommendations. The panel's recommendations were reviewed and approved by the NAMS Board of Trustees.

RESULTS

Osteoporosis, whose prevalence is especially high among elderly postmenopausal women, increases the risk of fractures. Hip and spine fractures are associated with particularly high morbidity and mortality in this population. Given the health implications of osteoporotic fractures, the primary goal of osteoporosis therapy is to prevent fractures, which is accomplished by slowing or stopping bone loss, maintaining bone strength, and minimizing or eliminating factors that may contribute to fractures. The evaluation of postmenopausal women for osteoporosis risk requires a medical history, physical examination, and diagnostic tests. Major risk factors for postmenopausal osteoporosis (as defined by bone mineral density) include advanced age, genetics, lifestyle factors (such as low calcium and vitamin D intake, smoking), thinness, and menopause status. The most common risk factors for osteoporotic fracture are advanced age, low bone mineral density, and previous fracture as an adult. Management focuses first on nonpharmacologic measures, such as a balanced diet, adequate calcium and vitamin D intake, adequate exercise, smoking cessation, avoidance of excessive alcohol intake, and fall prevention. If pharmacologic therapy is indicated, government-approved options are bisphosphonates, a selective estrogen-receptor modulator, parathyroid hormone, estrogens, and calcitonin.

CONCLUSIONS

Management strategies for postmenopausal women involve identifying those at risk of low bone density and fracture, followed by instituting measures that focus on reducing modifiable risk factors through lifestyle changes and, if indicated, pharmacologic therapy.

Molecular pathways mediating mechanical signaling in bone

Bone tissue has the capacity to adapt to its functional environment such that its morphology is "optimized" for the mechanical demand. The adaptive nature of the skeleton poses an interesting set of biological questions (e.g., how does bone sense mechanical signals, what cells are the sensing system, what are the mechanical signals that drive the system, what receptors are responsible for transducing the mechanical signal, what are the molecular responses to the mechanical stimuli). Studies of the characteristics of the mechanical environment at the cellular level, the forces that bone cells recognize, and the integrated cellular responses are providing new information at an accelerating speed. This review first considers the mechanical factors that are generated by loading in the skeleton, including strain, stress and pressure. Mechanosensitive cells placed to recognize these forces in the skeleton, osteoblasts, osteoclasts, osteocytes and cells of the vasculature are reviewed. The identity of the mechanoreceptor(s) is approached, with consideration of ion channels, integrins, connexins, the lipid membrane including caveolar and non-caveolar lipid rafts and the possibility that altering cell shape at the membrane or cytoskeleton alters integral signaling protein associations. The distal intracellular signaling systems on-line after the mechanoreceptor is activated are reviewed, including those emanating from G-proteins (e.g., intracellular calcium shifts), MAPKs, and nitric oxide. The ability to harness mechanical signals to improve bone health through devices and exercise is broached. Increased appreciation of the importance of the mechanical environment in regulating and determining the structural efficacy of the skeleton makes this an exciting time for further exploration of this area.

Novel, high-frequency, low-strain mechanical loading for premenopausal women with low bone mass: early findings

Universally safe and effective methods of mechanically loading the skeleton to improve strength and prevent fracture have yet to be identified. To be osteogenic, mechanical strains must either be of substantial magnitude or applied at high frequency (>15 Hz). High-magnitude loads place frail bones at risk of fracture. Active loading can rarely be achieved at a frequency faster than 2-3 Hz. A 12-month, uncontrolled, prospective, pilot intervention trial was conducted with five premenopausal Caucasian women with low bone mass. Subjects stood on a vibrating platform (Optimass model 1000 Mechanical Strain Device) and received a 0.2-g stimulus at 30 Hz, 2 x 10 min/day, for 12 months. Bone mineral density (BMD) was measured at the whole body, lumbar spine, proximal femora (PF), and distal radius at baseline and 6 and 12 months by DXA (Hologic QDR-1000/W). Blood and urine were collected at baseline and 3, 6, 9 and 12 months for markers of bone resorption and formation. A mean percent BMD increase of 2.03% +/- 0.33% (P < 0.02) was detected at the non-dominant PF after 12 months. Trends for increases were observed at all other sites with the exception of the dominant PF. No uniform trends were observed in bone resorption and formation markers. One subject, on Fosamax, increased BMD by 6% at the lumbar spine and 4.4% at the distal radius. Preliminary findings provide evidence of a possible positive response of regions of low bone mass to brief daily bouts of in-home, passive, noninvasive, low-strain, high-frequency, mechanical loading.

Whole body vibration exercise: are vibrations good for you?

Whole body vibration has been recently proposed as an exercise intervention because of its potential for increasing force generating capacity in the lower limbs. Its recent popularity is due to the combined effects on the neuromuscular and neuroendocrine systems. Preliminary results seem to recommend vibration exercise as a therapeutic approach for sarcopenia and possibly osteoporosis. This review analyses state of the art whole body vibration exercise techniques, suggesting reasons why vibration may be an effective stimulus for human muscles and providing the rationale for future studies.

Establishing the compliance in elderly women for use of a low level mechanical stress device in a clinical osteoporosis study

Non-pharmacologic approaches to prevent bone loss are well suited for elderly patients to avoid polypharmacy and medication side effects. One potential treatment is a vibrating platform that delivers low-level mechanical loading stimulating bone remodeling. However, compliance is a major concern with any daily treatment, and is unknown for an elderly group using this device. Thus we assessed compliance with standing 10 min/day on a vibrating platform device in elderly women, the target population for osteoporosis therapy. We also assessed satisfaction with daily use of the device. We conducted a randomized, placebo-controlled, double-blinded 6-month study for daily use of a 10-min vibrating platform treatment in elderly women who were residents of a Continuing Care Retirement community. Compliance for each subject was calculated as the number of days attended divided by the 182 days in the 6-month trial. The 24 elderly women (mean age 86, range 79-92 years) had 83% compliance (95% CI: 70.5, 94.5) for daily treatment over 6 months. Excluding three study drop-outs, the 21 women had 93% compliance (95% CI: 89.8, 95.6), with no difference in compliance between active and placebo treatment. Main reasons for missing treatment days over the 6 months were vacation (54% of missed days) and illness (29%). Three adverse events occurred; one (syncope) was possibly related to device use, whereas the other two were not related to device use. Among participants, 95% reported overall satisfaction with daily use of the vibrating platform, and 57% preferred the platform versus daily oral medications for prevention of bone loss. Elderly women showed high compliance, high satisfaction and few adverse experiences with a daily non-pharmacological treatment designed to inhibit bone loss. Larger randomized controlled trials should evaluate the long-term efficacy of vibrating platform devices for treatment of low bone mass and osteoporosis in elderly individuals.

Signal transduction and mechanical stress

Bone undergoes a constant process of remodeling in which mass is retained or lost in response to the relative activity of osteoblasts and osteoclasts. Weight-bearing exercise-which is critical for retaining skeletal integrity-promotes osteoblast function, whereas a lack of mechanical stimulation, as seen during spaceflight or prolonged bed rest, can lead to osteoporosis. Thus, understanding mechanotransduction at the cellular level is key to understanding basic bone biology and devising new treatments for osteoporosis. Various mechanical stimuli have been studied as in vitro model systems and have been shown to act through numerous signaling pathways to promote osteoblast activity. Here, we examine the various types of stress and the sequential response of transduction pathways that result in changes in gene expression and the ensuing proliferation of osteoblasts.

Low magnitude mechanical loading is osteogenic in children with disabling conditions

The osteogenic potential of short durations of low-level mechanical stimuli was examined in children with disabling conditions. The mean change in tibia vTBMD was +6.3% in the intervention group compared with -11.9% in the control group. This pilot randomized controlled trial provides preliminary evidence that low-level mechanical stimuli represent a noninvasive, non-pharmacological treatment of low BMD in children with disabling conditions.

INTRODUCTION

Recent animal studies have demonstrated the anabolic potential of low-magnitude, high-frequency mechanical stimuli to the trabecular bone of weight-bearing regions of the skeleton. The main aim of this prospective, double-blind, randomized placebo-controlled pilot trial (RCT) was to examine whether these signals could effectively increase tibial and spinal volumetric trabecular BMD (vTBMD; mg/ml) in children with disabling conditions.

MATERIALS AND METHODS

Twenty pre-or postpubertal disabled, ambulant, children (14 males, 6 females; mean age, 9.1 +/- 4.3 years; range, 4-19 years) were randomized to standing on active (n = 10; 0.3g, 90 Hz) or placebo (n = 10) devices for 10 minutes/day, 5 days/week for 6 months. The primary outcomes of the trial were proximal tibial and spinal (L2) vTBMD (mg/ml), measured using 3-D QCT. Posthoc analyses were performed to determine whether the treatment had an effect on diaphyseal cortical bone and muscle parameters.

RESULTS AND CONCLUSIONS

Compliance was 44% (4.4 minutes per day), as determined by mean time on treatment (567.9 minutes) compared with expected time on treatment over the 6 months (1300 minutes). After 6 months, the mean change in proximal tibial vTBMD in children who stood on active devices was 6.27 mg/ml (+6.3%); in children who stood on placebo devices, vTBMD decreased by -9.45 mg/ml (-11.9%). Thus, the net benefit of treatment was +15.72 mg/ml (17.7%; p = 0.0033). In the spine, the net benefit of treatment, compared with placebo, was +6.72 mg/ml, (p = 0.14). Diaphyseal bone and muscle parameters did not show a response to treatment. The results of this pilot RCT have shown for the first time that low-magnitude, high-frequency mechanical stimuli are anabolic to trabecular bone in children, possibly by providing a surrogate for suppressed muscular activity in the disabled. Over the course of a longer treatment period, harnessing bone's sensitivity to these stimuli may provide a non-pharmacological treatment for bone fragility in children.