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JOURNAL OF BONE AND MINERAL RESEARCH
Volume 19, Number 3, 2004
Published online on December 22, 2003; doi: 10.1359/JBMR.0301245
2004 American Society for Bone and Mineral Research
Effect of 6-Month Whole Body Vibration Training on Hip Density, Muscle Strength, and Postural Control in Postmenopausal Women: Sabine MP Verschueren,1 Machteld Roelants,2 Christophe Delecluse,2 Stephan Swinnen,1 ABSTRACT: High-frequency mechanical strain seems to stimulate bone strength in animals. In this random-
ized controlled trial, hip BMD was measured in postmenopausal women after a 24-week whole body vibration
(WBV) training program. Vibration training significantly increased BMD of the hip. These findings suggest
that WBV training might be useful in the prevention of osteoporosis.
Introduction: High-frequency mechanical strain has been shown to stimulate bone strength in different animal
models. However, the effects of vibration exercise on the human skeleton have rarely been studied. Particularly in
postmenopausal women—who are most at risk of developing osteoporosis—randomized controlled data on the safety
and efficacy of vibration loading are lacking. The aim of this randomized controlled trial was to assess the
musculoskeletal effects of high-frequency loading by means of whole body vibration (WBV) in postmenopausal
women.
Materials and Methods: Seventy volunteers (age, 58 –74 years) were randomly assigned to a whole body vibration
training group (WBV, n ϭ 25), a resistance training group (RES, n ϭ 22), or a control group (CON, n ϭ 23). The
WBV group and the RES group trained three times weekly for 24 weeks. The WBV group performed static and
dynamic knee-extensor exercises on a vibration platform (35– 40 Hz, 2.28 –5.09g), which mechanically loaded the
bone and evoked reflexive muscle contractions. The RES group trained knee extensors by dynamic leg press and leg
extension exercises, increasing from low (20 RM) to high (8 RM) resistance. The CON group did not participate in
any training. Hip bone density was measured using DXA at baseline and after the 6-month intervention. Isometric
and dynamic strength were measured by means of a motor-driven dynamometer. Data were analyzed by means of
repeated measures ANOVA.
Results: No vibration-related side effects were observed. Vibration training improved isometric and dynamic muscle
strength (ϩ15% and ϩ 16%, respectively; p Ͻ 0.01) and also significantly increased BMD of the hip (ϩ0.93%, p Ͻ
0.05). No changes in hip BMD were observed in women participating in resistance training or age-matched controls
(Ϫ0.60% and Ϫ0.62%, respectively; not significant). Serum markers of bone turnover did not change in any of the
groups.
Conclusion: These findings suggest that WBV training may be a feasible and effective way to modify well-
recognized risk factors for falls and fractures in older women and support the need for further human studies.
J Bone Miner Res 2004;19:352–359. Published online on December 22, 2003; doi: 10.1359/JBMR.0301245
Key words:
whole body vibration, mechanical loading, resistance training, osteoporosis
INTRODUCTION
cation of osteoporosis. The mortality rate in patients withhip fracture is 12–20% higher than in persons of similar age AS THE WORLD POPULATION ages, osteoporosis and osteo- and gender who have not suffered a fracture.(2) Of those porotic fracture occurrence are becoming an increas- who survive the operative intervention for an osteoporotic ingly important public health problem.(1) By any measure, hip fracture, less than one-third are restored to their prefrac- proximal femoral fracture is the most devastating compli- ture functional state.(3) Most strategies to treat postmeno-pausal bone loss have been focusing on antiresorptive med- The authors have no conflict of interest.
ication. More recently, the potential contribution of load- 1Laboratory of Motor Control, Department of Kinesiology, Faculteit Lichamelijke Opvoeding en Kinesitherapie, Katholieke Univer- siteit, Leuven, Belgium; 2Laboratory of Exercise Physiology and Biomechanics, Department of Kinesiology, Faculteit LichamelijkeOpvoeding en Kinesitherapie, Katholieke Universiteit, Leuven, Belgium; 3Leuven University Center for Metabolic Bone Diseases andDivision of Endocrinology, Katholieke Universiteit, Leuven, Belgium; 4Leuven University Center for Metabolic Bone Diseases andDivision of Geriatric Medicine, Faculty of Medicine, Katholieke Universiteit, Leuven, Belgium.
EFFECT OF WHOLE BODY VIBRATION ON BONE DENSITY AND MUSCLE STRENGTH
TABLE 1. BASELINE CHARACTERISTICS OF THE VIBRATION GROUP (WBV), THE RESISTANCE GROUP (RES), bearing exercise to preserve bone density and prevent founded by degenerative changes and is highly predictive of osteoporosis has received some attention. In this regard, a relatively vigorous aerobic and strength training regimenhas been shown to be most effective.(4) However, this ap- MATERIALS AND METHODS
proach has the inherent disadvantage of a lack of long-term compliance and may even increase the risk of fracture.(5) Itis therefore imperative to continue the search for more Seventy postmenopausal women volunteered to partici- attractive, low-risk exercise programs, with the goal of pate in the study. Assessment of eligibility for participation was based on a screening by questionnaire and a thorough Recently, Rubin et al.(6) provided evidence in an animal medical examination. Women had to be between 60 and 70 model that low-risk, high-frequency mechanical accelera- years of age, non-institutionalized, and free from diseases or tions may have a strong osteogenic effect. In their study, medications known to affect bone metabolism or muscle they observed a dramatic increase of the quality and quan- strength. Subjects with a total body BMD T-score of less tity of trabecular bone in sheep when exposed to low-level, than Ϫ2.5 (the WHO definition for osteoporosis) were also high-frequency mechanical stimuli. A high-frequency load- excluded from this study. All subjects were randomly as- ing regimen applied to ovariectomized rats was effective in signed to one of the study groups using computer-generated preventing early post-ovariectomy bone loss.(7) Overall, random numbers. A total of 25 women were trained for 6 these experiments have given evidence that vibration load- months on a vibrating platform (WBV group). A group of ing may have potential for preventing and treating osteopo- 22 woman participated in a resistance training program rosis. However, in postmenopausal women—who are most (RES group). Both training programs consisted of 72 train- at risk of sustaining osteoporotic fractures—the impact of ing sessions within a 24-week period. Training frequency this type of approach on bone quality (and, by implication, was three times a week, with at least 1 day of rest between potentially on fracture risk) has not been evaluated.
two sessions. A group of 23 age-matched women served as The aim of this randomized controlled trial was therefore a control group (CON group) and did not participate in any to assess musculoskeletal effects of high-frequency whole training. The baseline characteristics of both groups are body vibration (WBV) training in postmenopausal women.
indicated in Table 1. All participants gave their informed Vibration training is increasingly being promoted as a safe written consent before enrollment, and the study protocol and efficient training method to improve muscle strength.(8) was approved by the Leuven University Human Ethics During a vibration session, the subject stands on a platform that generates vertical sinusoidal vibrations at a frequency between 35 and 40 Hz. The mechanical stimuli are trans-mitted to the body, where they load the bone and also The subjects in the WBV group performed static and stimulate sensory receptors (most likely muscle spindles).
dynamic knee-extensor exercises on the vibration platform The activation of these sensory receptors results in reflexive (PowerPlate, Amsterdam. The Netherlands): squat, deep activation of motor units similar to the tonic vibration squat, wide stance squat, one-legged squat, and lunge.
Training load was low at the beginning but progressed We hypothesized that, in addition to an increase in mus- slowly according to the overload principle.(11) The training cle strength caused by vibration-induced muscle activity, volume increased systematically over the 6-month training high-frequency loading of the skeleton might improve the period by increasing the duration of one vibration session, mechanical competence of the skeleton in postmenopausal the number of series of one exercise, or the number of women. BMD of the total hip was selected as primary different exercises. The training intensity was increased by endpoint of this trial because the measurement is not con- shortening the rest periods or by increasing the amplitude VERSCHUEREN ET AL.
Increased muscle activation in the m.
rectus femoris and the m. gastrocnemius duringvibrating training. RMS is the root mean squareof the rectified EMG in the period without orwith vibration.
(low, 1.7 mm; high, 2.5 mm) and/or the frequency (35– 40 Hz) of the vibration. In addition, training load was increased Control subjects were instructed to maintain their current by changing the execution form of the exercises from pre- level of physical activity during the 24 weeks of the study dominantly two-legged to one-legged exercises. The dura- and not to engage in any new form of exercise. The subjects tion of the WBV program was a maximum of 30 minutes, completed a questionnaire detailing their physical activity at which included warming up and cooling down.
the beginning of the study and at monthly intervals there- The peak acceleration of the sinusoidal vibration stimulus—as recorded by an accelerometer (MTN 1800;Monitran, Bucks, UK)—varied between 2.28g and 5.09g (root mean square acceleration between 13.5 and 34.6 m/s2).
Of the 5g acceleration, as measured on the platform, only a At baseline and at 6 months, areal BMD of the total hip fraction is transmitted through the feet to the hip and spine.
and the total body was assessed by DXA using the QDR- However, the exact degree of transmissibility is unknown.
4500A device (Hologic, Waltham, MA, USA). Standard Bipolar surface EMGs (Myosystem 2000; Noraxon, Scotts- positioning was used, with anterior–posterior scanning of dale, AZ, USA) recorded from m. rectus femoris and from the right proximal femur.(14) Lean body mass, fat mass, and m. gastrocnemius illustrate the impact of the vibration on percent fat were obtained from the DXA scan of the total muscle activity (Fig. 1). During the vibration training ses- body. All scans were performed by the same experienced sions, the subjects wore similar gymnastic shoes to stan- technician, who was unaware of the patient’s intervention dardize the damping of the vibration cause by foot wear.
type. The CV for total hip DXA measurement in our labo-ratory is 0.56%.
The subjects of the RES group trained in the Leuven University fitness center. They started with a standardized At baseline and at 6 months, serum osteocalcin and warm-up consisting of 20 minutes of stepping, running, or C-telopeptide levels (CTX) were determined as markers of cycling. The intensity of these cardiovascular exercises was bone formation and resorption, respectively. At these time automatically controlled by heart rate (Technogym Sys- points, fasting blood samples were collected from all indi- tems, Gambettola, Italy) and systematically increased from viduals and stored at Ϫ70°C until they were analyzed.
60% to 80% of the heart rate reserve as calculated by the Circulating osteocalcin was measured using a previously formula of Karvonen.(12) After the warm-up, the partici- developed radioimmunoassay (RIA).(15) Serum CTX was pants performed a resistance training program for knee assessed by Serum CrossLaps One-Step ELISA (Osteom- extensors on a leg extension and a leg press machine (Tech- eter BioTech, Herlev, Denmark) by a method previously nogym Systems). The resistance training program was de- signed according to the guidelines of the American Collegeof Sports Medicine (ASCM) for individuals older than 60 years of age: 10 –15 repetitions to the point of volitionalfatigue to elicit improvement in both muscular strength and The strength of the knee extensors was evaluated on a endurance.(13) During the first 14 weeks of training, the motor-driven dynamometer (REV9000; Technogym Sys- intensity was systematically increased from two sets of 20 tems) by isometric tests and dynamic tests.
repetition maximum (RM) to two sets of 15 RM, two sets of Isometric strength: The subjects performed a maximal 12 RM, two sets of 10 RM, and finally two sets of 8 RM. In voluntary isometric contraction of the knee extensors twice.
the last 10 weeks, training volume and training intensity The knee joint angle was 130°. The isometric contractions varied between three sets of 12 RM and one set of 8 RM.
lasted 3 s each and were separated by a 2-minute rest Each RES program lasted for about 1 h in total.
interval. The highest torque (N.m) was recorded as isomet- EFFECT OF WHOLE BODY VIBRATION ON BONE DENSITY AND MUSCLE STRENGTH
ric strength performance. The CV for isometric strength TABLE 2. MEAN CHANGES AND BETWEEN-GROUP DIFFERENCES IN measurement in our laboratory is 3.7%.
MUSCLE STRENGTH, HIP BONE DENSITY, AND BODY COMPOSITION Dynamic strength: The subjects performed a series of four consecutive isokinetic flexion– extension movements against the lever arm of the dynamometer that moved at a velocity of 100°/s. The knee extension was initiated at a joint angle of 90° and ended at 160°. After each extension,the leg was returned passively to the starting position from which the next contraction was immediately initiated. Max- imal dynamic strength was determined as the peak torque (N.m) recorded during these series of knee extensions. The CV for dynamic strength measurement in our laboratory is Postural sway was measured before and after the 24 week period using a Bertec force plate connected to a CED Micro1401 data acquisition system and using spike2 software.
Postural sway of each subject was tested under four condi- tions: quiet stance with vision, quiet stance with vision occluded by means of liquid-cristal goggles, quiet stance after a perturbation by a brief voluntary abduction of the arms to horizontal, and quiet stance after a brief anteflexion of the arms to horizontal. Postural sway was assessed in the WBV group and CON group, but not in the RES group.
A one-way ANOVA was used to test for baseline differ- ences among the WBV group, the RES group, and the CON group. The effects of the interventions were analyzed by means of repeated measures ANOVA. After an F value was found to be significant for the interaction between group and time, preplanned contrast analyses were performed to eval- uate significant pre–post changes in each group. A Bonfer-roni correction was used to adjust the p value in relation tothe number of contrasts that were performed. All analyseswere executed using the statistical package Statistica (ver- significant change was observed (ϩ2.2%; 95% CI, Ϫ1.5– sion 6; Statsoft, Hamburg, Germany.). The level of signif- 5.9; p ϭ 1.14). Again, both the WBV and RES groups showed a significant net benefit over time compared withthe CON group (ϩ14.2% and ϩ 8.4%, respectively; p Ͻ As shown in Fig. 2, total hip BMD increased over time in No significant differences were observed at baseline be- the WBV training group (ϩ0.93%; 95% CI, 0.13–1.71; p ϭ tween the experimental and the control groups in terms of 0.03), whereas no changes in hip BMD were observed in age, weight, body mass, years since menopause, BMD, women participating in resistance training or age-matched serum levels of osteocalcin and CTX, isometric and dy- controls (Ϫ0.51%; 95% CI, Ϫ1.13 to Ϫ0.11; p ϭ 0.41 and namic muscle strength, fat mass, or lean body mass (Ta- Ϫ0.62%; 95% CI, Ϫ1.30–0.07; p ϭ 0.16, respectively).
Compared with the RES group, the 6-month vibration in- Isometric strength of the knee extensors increased by tervention resulted in a significant 1.51% net benefit in total 15% (95% CI, 10.6 –19.5; p Ͻ 0.001) in the WBV group hip BMD (p Ͻ 0.05). A similar net benefit (1.53%, p Ͻ and by 16% in the RES group (95% CI, 9.1–23.9; p Ͻ 0.01) was observed in comparison with the CON group. The 0.001). In the control group, a nonsignificant decline of 2% gain in total hip BMD in the WBV group was statistically was observed (95% CI, Ϫ6.9 –2.01; p ϭ 0.57). Compared unrelated to the increases in isometric or dynamic strength with the CON group, the 6-month vibration intervention (r ϭ Ϫ0.23, p ϭ 0.29 and r ϭ 0.28, p ϭ 0.20, respectively).
resulted in a significant 17.6% net benefit in isometric Total body BMD and lumbar spine BMD did not change quadriceps strength (p Ͻ 0.001; Table 2). A similar benefit over time in any of the groups, and none of the between- was observed in the RES group (ϩ18.9% versus the CON group differences were statistically significant. Similarly, no significant between-group differences were observed in the Dynamic strength increased by 16.5% (95% CI, 9.4 – markers of bone remodeling, osteocalcin, and CTX (Table 3).
23.5) and 10.6% (95% CI, 5.6 –15.5) in the WBV group and The gain in muscle strength in the WBV and RES groups RES group, respectively (p Ͻ 0.001). In the controls, no was not associated with a significant change in lean body VERSCHUEREN ET AL.
DISCUSSION
There is increasing evidence that load-bearing represents a very important functional influence on bone mass.(5) In-creased bone density after loading shows that bone tissueaccommodates to changes in the mechanical environment;this process allows the skeleton to resist the rigors of func-tional activity.(17,18) However, particularly in elderly indi-viduals, strenuous load-bearing exercises may increase therisk for injuries.(19) Moreover, there is evidence that theosteogenic effect of load-bearing may decline with ag-ing.(20) The search therefore continues for alternative strat-egies that make loading less risky and/or may enhance theeffectiveness of the adaptive bone response to loading. Thetraining paradigm presented here might potentially offersuch a strategy for postmenopausal woman, because theresults show that 24 weeks of WBV training—which me-chanically loads the bone and evokes reflexive musclecontractions—was not associated with vibration-related sideeffects and resulted in increased hip BMD. The meanchange in total hip BMD in the WBV group (with a netbenefit of about 1.5% at 6 months compared with controls)is similar in magnitude to the gain in (hip) BMD observedwith antiresorptive agents at the 6-month time point inrecent osteoporosis trials,(21,22) supporting its potential clin-ical relevance. We found no effect of the vibration inter-vention on bone turnover rate, indicating that its positiveimpact on BMD did not result from reduced bone resorp-tion. In line with the lack of significant changes in overallrate of bone turnover, no changes were observed in totalbody or lumbar spine BMD, suggesting that the effects ofvibration on total hip BMD reflect a local (site-specific)loading effect of vibration.
In addition to their gain in BMD, and not unexpectedly,(8) the subjects in the vibration group showed improved recov-ery of balance after ballistic abduction or anteflexion of thearms and experienced an increase in (isometric and isoki-netic) muscle strength and a decline in fat mass. The Percent changes across 24 weeks in (A) isometric and dy- changes in muscle strength were similar in magnitude than namic muscle strength, (B) total body and total hip BMD, and (C) leanand fat mass in the three experimental groups (WBV, RES, and CON).
those in the resistance training group. The gain in BMDduring the 6-month intervention, however, was statisticallyunrelated to the increases in isometric or dynamic strength, mass (Table 3). However, in both groups, total fat mass suggesting that the osteogenic effect was not mediated by decreased significantly during the intervention period reflexive muscle contractions. This assumption is supported (Ϫ2.3%; 95% CI, Ϫ4.3 to Ϫ0.4; p ϭ 0.01 in the WBV by the fact that the gain in lower limb extension strength in group and Ϫ3.1%; 95% CI, Ϫ4.9 to Ϫ1.3; p Ͻ 0.001 in the the resistance training group was not paralleled by a con- RES group). In contrast, no significant change in fat mass was observed in the CON group (ϩ0.5%; 95% CI, Ϫ1.3– Controlled loading studies have indicated that high strain magnitudes and high strain rates are the most osteo- The effects of WBV training on postural sway are sum- genic.(23,24) The loading regimen provided by the WBV marized in Table 4. Postural sway (rms and peak-to-peak program in this study combined both. It has been commonly amplitude) during unperturbed stance with or without vision assumed that the large amplitude signals inherent to intense did not change because of WBV training (data not shown).
functional activity define bone morphology.(25) Strain on the After a fast, brief abduction of the arms, the peak-to-peak bones increases linearly with increased ground reaction amplitude of sway in the anterior–posterior direction was forces.(26) In our study, the ground reaction forces ranged significantly decreased during the WBV training (p Ͻ 0.05).
between 2.5 times body weight at the start of the program to Similarly, the peak-to-peak amplitude of sway in medio– 5 times body weight from week 3 onward. The loading of lateral direction after a brief anteflexion of the arms was the skeleton during the vibration intervention can therefore significantly decreased because of WBV training (p ϭ be considered as a high-strain event of similar impact than 0.05). None of these variables changed across the 24 weeks activities like basketball, volleyball, and sprinting.(27) In this regard, the results of this trial are in agreement with previ- EFFECT OF WHOLE BODY VIBRATION ON BONE DENSITY AND MUSCLE STRENGTH
TABLE 3. MUSCLE STRENGTH, HIP BONE DENSITY, BONE TURNOVER, AND BODY COMPOSITION AT BASELINE AND *Group-by-time interaction in repeated measures ANOVA on pre–post data.
†,‡Significant pre–post difference within group (†p Ͻ 0.05 and ‡p Ͻ 0.01).
ous studies showing positive effects of high-impact exercise In a very recent well-designed study in young healthy regimens on bone density.(28) It has been hypothesized that adults, Torvinen et al.(31) found no effect of WBV training loading reduces the rate of bone resorption and increases on mass, structure, and estimated strength of bone. The bone formation in proportion to the peak strain magni- authors argued that one reason for this nonresponse could be tude.(23) However, while we observed an increase in hip the good basic physical condition of the young subjects, bone density in the vibration group within 6 months, posi- with the musculoskeletal tissues of these young adults hav- tive effects of high-impact exercises on BMD have not even ing no particular physiological need to adapt to the vibration been observed within the first year of training.(28) loading. They suggested that a skeletal response to vibration It is therefore tempting to speculate that the high fre- might have been observed in older individuals, as is the case quency of vibration (35– 40 Hz; i.e., the high strain rate) in our study. However, as Torvinen et al.(31) indicated as may have played a key role in the early osteogenic effect well, the vibration stimulus can be varied in multiple ways observed in this study. Whereas loads applied at 1 Hz must (including type, magnitude, frequency, and duration), and exceed 1000 microstrain to stimulate bone formation,(29) different types of vibration loading are likely to result in 30-Hz loads only need strains of 50 microstrain to achieve different effects on bone mass and structure. In their trial, similar results.(30) Animal research by Rubin et al.(6,17) has the duration of daily stimulus was only 4 minutes, three to provided evidence that these low-level, high-frequency me- five times per week, considerably less than the 20-minute chanical stimuli may be anabolic to (trabecular) bone. In stimulus in this study. Their stimulus might have been their experiments in adult female sheep, histomorphometric examination of the femur after 1 year of stimulation re- To date, the mechanism underlying the osteogenic effect vealed an increase in bone volume per total volume by 32%, of high-frequency stimuli is not completely understood.
resulting in a 27% improvement in trabecular bone strength.
Rubin et al.(17) hypothesized that the adaptive response of However, although bone morphology and structure were the bone to high-frequency stimuli may not be a direct dramatically being reinforced, no changes were identified consequence of bone tissue deformation (as during high- with DXA measurements. This made Rubin et al.(17) con- impact loading), but may rather be mediated by byproducts clude that when DXA does identify change, as in our trial, of the high-frequency strain signal, such as shear stress the change is likely to be relevant.
arising from fluid flow. Alternatively, the mechanism be- VERSCHUEREN ET AL.
TABLE 4. POSTURAL SWAY (PEAK-TO-PEAK) RECOVERY AFTER a significant increase in (total hip) BMD from baseline in ABDUCTION OR ANTEFLEXION OF THE ARMS AT BASELINE AND AFTER the vibration group and significant between-group differ- ences, we acknowledge that the number of observations was small. As indicated, we can only speculate about the mech- anisms underlying the increase in BMD and the extent to which this increase reflects differential effects on cortical and trabecular bone. Many questions remain as to whetherthese short-term effects would persist over time and as to how the training protocol can be further optimized in terms of osteogenic effects. We selected a training program on the vibration platform that was likely to have positive effects on muscle and bone tissue. It is possible that high-frequency or even broad-frequency vibration at a lower strain amplitude, superimposed with some larger strains at intermittent inter- vals, might be more osteogenic (but at the expense of gain in strength). Also, our results may not be generalizable because the participants were healthy volunteers and not a random sample of the general older population. Finally, the usefulness and safety of this type of training in the long- *Group-by-time interaction in repeated ANOVA on pre–post data.
term prevention of postmenopausal osteoporosis and osteo- †Significant pre–post difference within group ( p Ͻ 0.05).
porotic fracture occurrence remain unknown.
In conclusion, in healthy postmenopausal women, a 24- week whole body vibration program is feasible and able to hind the frequency-dependent adaptive response of bone to modify muscle strength, balance, and hip bone density, loading might be the so-called stochastic resonance. Sto- which are well-recognized risk factors for hip fracture.(10) chastic resonance is a phenomenon in which mechanical Future human studies are needed to confirm these short- noise (broad-band frequency of vibration) enhances the term findings and further explore the potential of vibration response of a nonlinear system to a weak signal by boosting loading for preventing and treating osteoporosis.
it over a threshold. Previous studies have shown that sto-chastic resonance can enhance the mechanosensitivity of ACKNOWLEDGMENTS
different mechanoreceptors in our body, like the musclespindles.(32) Recent in vitro and in vivo evidence suggests SB is a core member of the ASBMR Working Group on that (cortical) bone formation in response to mechanical Musculoskeletal Rehabilitation. The authors thank all the loading can be enhanced by adding noise to a (high-impact) participants for taking part in this study. They also thank G exercise regimen.(33,34) Tanaka et al.(33) showed that a vi- Van der Meer, J Tempelaars, and N De Poot for help in bratory stimulus added to a low-frequency, high-amplitude designing the training program; Drs E Van den Eede and K strain enhances the osteogenic response of the strain by Pardaens for the medical screening of the subjects; and H almost 4-fold. In the present trial, we applied both a large- Borghs and H Peeters for conducting the DXA measure- amplitude strain and a high-frequency vibratory stimulus.
ments. This study was supported by Grant G.0171.03 from Stochastic resonance may therefore have contributed to the (F.W.O.-Vlaanderen) to SB. SMPV is a postdoctoral fellow In certain professions (e.g., tractor drivers, pilots, etc.) a of the Fund for Scientific Research-Flanders, Belgium. SB (potential) association has been observed between long- and DV are senior clinical investigators of the Fund for term exposure to WBV and chronic lower back pain.(35) Scientific Research-Flanders, Belgium. SB is holder of the However, evidence in favor of a dose–response association Leuven University Chair in Metabolic Bone Diseases, sup- is weak, and it remains to be clarified whether there is a causal link between work-related WBV and low back pain.
As indicated, we observed no vibration-related side effects.
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