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Effects of Whole-Body Vibration Versus Pilates Exercise on Bone Mineral Density in Postmenopausal Women: A Randomized and Controlled Clinical Trial

de Oliveira, Laís Campos PT, PhD1; de Oliveira, Raphael Gonçalves PE, PhD1; de Almeida Pires-Oliveira, Deise Aparecida PT, PhD2

Author Information
Journal of Geriatric Physical Therapy: April/June 2019 - Volume 42 - Issue 2 - p E23-E31
doi: 10.1519/JPT.0000000000000184

Abstract

INTRODUCTION

The term “postmenopausal” refers to the stage of a woman's life that begins after the cessation of menstrual cycles.1 This stage is marked by alterations in the body that occur principally due to hormonal changes such as a reduction in estrogen levels, causing several factors that are detrimental to health.2 One of these factors is the decrease in bone mineral density (BMD), which can lead to osteoporosis and substantially increase the risk of fracture.3 Osteoporosis is more common than diabetes, heart attack, and stroke in older women.4 Approximately one-third of postmenopausal women have osteoporosis, and, of these, at least 40% will sustain 1 or more fragility fractures in their remaining lifetime,5 which can lead to morbidity and mortality.3

To mitigate these factors, different forms of treatment aimed at increasing BMD have been investigated in postmenopausal women.6–8 The use of medication is highlighted as a possible treatment method; however, the side effects limit their use in the long-term or when the individual has a predisposition for certain types of diseases.9 Thus, the use of alternative means to increase bone metabolism has been investigated, such as ensuring adequate intake of calcium and vitamin D, incorporating dietary supplements if the diet is not sufficient, and participating in regular weight-bearing and muscle-strengthening exercise.10

One of the forms of intervention that needs to be better studied, which has been shown to offer few adverse events and is considered relatively safe, is the therapy involving whole-body vibration (WBV).11 This technique uses an sinusoidal-shaped oscillations platform that offers mechanical stimulation to the human skeleton according to preestablished parameters.12,13 Different intensities (frequency and magnitude), types of vibration, and body positioning during WBV have been used without consensus regarding the best parameters to increase BMD.14 A recent systematic review and meta-analysis involving randomized controlled trials (RCTs) showed that low frequency, high magnitude, side-alternating vibration, and body positioning with semiflexed knees may be the best parameters for increasing BMD in postmenopausal women, principally in the lumbar spine and trochanter regions. However, the low number of RCTs and the poor methodological quality of some studies limit extrapolations, demonstrating the need for further studies.8

In addition to WBV, another alternative to using medication is the practice of exercises involving muscular strengthening. A systematic review and meta-analysis of RCTs demonstrated that progressive resistance exercises with a low number of repetitions and greater overload were efficient for increasing lumbar spine and femoral neck BMD in postmenopausal women, while no significant results were observed for resistance training involving low overload and a high number of repetitions.7 However, at the time the meta-analysis was performed, no study had investigated the effects of Pilates exercise on the BMD of postmenopausal women.7 Pilates makes use of progressive resistance exercises, with few repetitions and higher overload,15 and has become increasingly popular.16 To date, only 1 RCT has verified the effects of Pilates on the BMD of postmenopausal women, identifying significant improvements for the lumbar spine; however, other bone regions were not investigated.17

With this problem in mind, the objective of the present study was to verify the effects of WBV and Pilates exercise on the BMD of postmenopausal women. We hypothesized that the parameters chosen for WBV and the intervention protocol selected for Pilates practice would be able to provide an increase in BMD in this population. Still, taking into account the existing evidence to date, we hypothesized that WBV should be superior to Pilates exercises to increase BMD.

METHODS

This is an RCT (registered at www.clinicaltrials.gov on May 7, 2016: NCT02769143), which followed the CONSORT recommendations (Supplementary Table 1, Supplemental Digital Content, available at: http://links.lww.com/JGPT/A216) and had a duration of 6 months, involving 51 women within the postmenopausal period (having experienced menopause for at least 1 year), subdivided into 3 groups of equal size. All participants were apparently healthy, aged between 40 and 70 years, living in the city of Jacarezinho, Paraná State, Brazil. The present study followed the ethical norms established in the Declaration of Helsinki (1975, revised in 1983) and was approved by the Human Research Ethics Committee of the Northern University of Paraná, Brazil (opinion 1,032,182). Informed consent was obtained from all individual participants included in the study.

Recruitment and Participants

Participants were recruited in May 2016, through posters in public places, advertisements in printed newspapers, radios, internet news sites, newsletters intended for medical clinics, and health facilities, all with local coverage, until the target sample size was reached (51 participants). The sample calculation was performed in the statistical program Bioestat 5.3 (Instituto Mamiraua, Amazonas, Brazil), taking into account the values for the areal bone mineral density (aBMD) for the lumbar spine measured by dual-energy x-ray absorptiometry (DXA) in a previous study.18 In this case, the weighted mean difference (its respective standard deviation) between the vibration and control groups—0.017 (0.029) and −0.004 (0.011), respectively—was used, in absolute alteration (g/cm2) between pre- and postintervention, with a test power of 80% and an α value of .05, which generated the need for 17 participants in each group.

The inclusion criteria were (a) postmenopausal, clinically confirmed at medical appointment, for at least 12 months; (b) not practicing physical exercise for at least 6 months; (c) agreement not to practice another type of exercise during the research; (d) ability to perform activities of daily living without assistance19,20; (e) presentation of a medical release indicating fitness for exercise; and (f) a score 19 or more on the Mini-Mental State Examination.21

The exclusion criteria were (a) musculoskeletal dysfunctions in the spine or lower limbs in the previous 6 months; (b) fracture in the vertebral column or the lower limbs after 40 years of age; (c) prosthesis in the lower limbs or implants in the vertebral column; (d) secondary causes of loss of bone mass; (e) other metabolic bone diseases or diseases that affect bone metabolism; (f) history of cancer in the previous 5 years; (g) vascular alterations, epilepsy, or seizures; (h) arrhythmia; (i) the use of a pacemaker; (j) eye disease affecting the retina; (k) cardiorespiratory diseases; (l) diseases of the neuromuscular system; (m) labyrinthitis or vertigo; (n) hospitalization in the previous 6 months for surgical reasons; (o) thyroid alteration; (p) smoking; (q) frequent use of alcoholic beverages; (r) use of supplements based on calcium or vitamin D, isoflavone, medication to increase BMD muscle mass in the previous 12 months; and (s) inability to tolerate WBV for 5 minutes.

All participants included in the present study were instructed to maintain their usual routines, as well as their daily physical activities (eg, sweeping the house or washing dishes) and nutritional habits. They were also instructed not to use any medication or supplements that could influence muscle mass or BMD (including soy and its derivatives).

Evaluation of BMD

Soon after the end of the recruitment period, the participants were submitted to bone mass evaluation through DXA equipment (Hologic QDR 1000 Plus, Waltham, Massachusetts). aBMD was expressed in absolute values (g/cm2). For the initial classification of participants, the criteria of the World Health Organization were used,22 in T-score values (difference in the standard deviation of the bone mass with reference to the average of young adults): no alteration (T >−1), osteopenia (T between −1 and −2.5), and osteoporosis (T <−2.5). Six different bone regions were considered: lumbar spine (L1-L4), femoral neck, total hip, trochanter, intertrochanter, and ward's area. The procedure was performed by an independent evaluator, not directly involved in the research project, with experience in DXA assessment of aBMD and blinded to the allocation of participants in each group. Calibration of the device was performed daily prior to the start of the assessments to ensure the same aBMD measurement conditions for all participants. Variation coefficients for this device were 1.3% for the lumbar spine, 1.4% for the femoral neck, and 1.2% for the total hip in precision studies.23 The same equipment, evaluator, and procedures used at baseline were repeated at follow-up (after 6 months).

Randomization

After the aBMD assessment, the participants were submitted to the randomization process (random allocation of participants into 1 of the 3 groups), performed by a blind researcher who was not part of the study team. The random numbers were generated by specific software (randomization.com), which distributed the participants into 3 groups: vibration group (VG), Pilates group (PG), and control group (CG), with 17 participants in each. The same researcher who carried out the randomization process sealed the dark envelopes containing the group of each participant in and delivered them to the principal investigator who remained blind regarding the allocation of the participants in each group. The blinded participants then individually received the envelope containing their name and the name of their group.

Intervention

Interventions occurred 3 times a week on nonconsecutive days for 6 months beginning in June 2016. The experimental groups (VG and PG) were supervised by 2 physiotherapists with professional experience in WBV therapy and Pilates. As the intervention was with exercise, it was not possible to blind the participants and the physiotherapists responsible for the interventions in relation to the therapy. The participants were instructed during 6 months of intervention not to perform another type of exercise.

Vibration group

The VG was exposed to WBV for 5 minutes on a sinusoidal-shaped oscillations platform, side-alternating vibration (Supplementary Figure 1, Supplemental Digital Content, available at: http://links.lww.com/JGPT/A214) (Arktus, Cascavel, PR, Brazil), which oscillates through an anteroposterior axis, causing the right and left sides to alternate horizontally. A frequency of 20 Hz (1 Hz = 1 oscillation/second) was used and a peak-to-peak displacement of 4 mm (with reference to the second toe), resulting in a magnitude of 31.5 m/s2 or 3.2 g (gravity: 1 g = 9.8 m/s2). Participants were instructed to stand on the platform oscillation plate, with the knees semiflexed at 30° and bare feet spaced at a distance of 50 cm, keeping the torso upright and holding the platform support with both hands. No accessories (such as an ethylene vinyl acetate plate) were placed on the platform's oscillating plate to cushion the impacts. All the parameters used in the equipment and the positioning of the participants were maintained throughout 6 months of intervention. A slippage test ensured that the feet of the participants always remained in contact with the oscillating plate during WBV.13

The intensity of WBV is mainly defined by the frequency and magnitude parameters, which are considered low when 20 Hz or less and less than 1 g, respectively. In this study, low frequency and high magnitude were used. These parameters, type of vibration, time of exposure, and body positioning of the participants were chosen based on a recent systematic review and meta-analysis that demonstrated that they are potentially the most effective for increasing BMD in postmenopausal women.8

Pilates group

The first session of the PG was used to familiarize participants with Pilates, providing an explanation of the correct execution of each movement and a better understanding of the principles of the method. The following equipment was used to perform the exercises: cadillac, reformer, ladder barrel, wall unit, chair, spine corrector, and small barrel (Supplementary Figure 2, Supplemental Digital Content, available at: http://links.lww.com/JGPT/A15) (ISP, Cascavel, PR, Brazil). Twenty-one strengthening and stretching exercises were selected for the main body segments: (a) lower limbs; (b) flexors, extensors, and lateral flexors of the trunk; and (c) upper limbs. Two exercise protocols were applied during 6 months of intervention, each performed for 3 months (Supplementary Table 2, Supplemental Digital Content, available at: http://links.lww.com/JGPT/A17). The duration of each session was 60 minutes. The intervention protocols were developed specifically for this study, aiming to improve the BMD of the evaluated regions.

All exercises were performed in 1 series of 10 repetitions, with a 1-minute rest interval between exercises. The intensity of the work overload in Pilates is principally determined by the spring, which was modified according to the evolution of the force of the participants (changing the positioning of the springs in the equipment, or changing the spring to another one of greater resistance),24 always maintaining the number of repetitions and series. To determine the level of effort of the participants and consequent evolution of the overload, a verbal description according to the Borg CR10 scale was used25: light load (Borg ≤ 2), moderate load (Borg > 2 and < 5), heavy load (Borg ≥ 5 and < 7), and close to maximum load (Borg ≥ 7). The level of perception of effort maintained during the sessions was heavy (Borg between 5 and 6). Whenever the intensity of the exercise was changed, the new load used was immediately annotated in an individual file, used for recording.

Control group

The CG did not carry out any type of intervention. The physiotherapist responsible for the study contacted the CG participants every month during 6 months of intervention to emphasize the importance of not exercising, not using alcohol or smoking, not consuming calcium, vitamin D, foods that contain isoflavones, supplements, or medications that could influence BMD or muscle mass. At this time the participants were also questioned about possible adverse events.

Adverse Events

A standardized form was used to record occurrences of adverse events in all 3 groups. The participants were questioned every month about any complication, such as muscle spasms or pains, joint pain, dizziness, falls, cramps, and changes in blood pressure.

Statistical Analysis

The normality of the data was verified by the Shapiro-Wilk test. Descriptive data are expressed as mean and standard deviation. The t test for independent samples was used to compare the number of participants' absences during the interventions (VG vs PG). The homogeneity of the variances was determined by the Levene test. To verify whether the 3 groups presented differences at baseline, 1-way analysis of variance was used for data with normal distribution (age, weight, height, BMI, and DXA measurement). Otherwise a Kruskal-Wallis test was calculated (time since menopause). The Pearson χ2 test was used for comparison between different conditions of BMD (no alterations, osteopenic, and osteoporotic). Intragroup changes between baseline and follow-up were analyzed via the t test for dependent samples. To verify the between-group differences for the bone parameters, covariance analysis was applied, with the follow-up data used as the dependent variable and baseline data as covariate. The Bonferroni post hoc was used for multiple comparisons between pairs (PG vs VG; VG vs CG; and PG vs CG). Intragroup and between-group effect sizes were calculated using Cohen's d, which was considered small (0.20), medium (0.50), or large (0.80).26 Initially, the data were analyzed using intention-to-treat (ITT) analysis, including all randomized subjects (missing data for the follow-up of 2 CG participants were imputed by the group mean). Subsequently, per-protocol analysis was performed, excluding the 2 participants from the CG who abandoned the study. As the results were similar, only the ITT analysis is presented in this report. For all tests, the level of significance adopted was 95% (P < .05). The analyses were processed in the SPSS 20.0 program (Chicago, Illinois), except for effect size calculations (Cohen's d), which were processed in GPower 3.1 (Franz Faul, Universität Kiel, Germany).

RESULTS

Adherence

After 6 months of intervention, 96.1% of participants completed the study. Two CG participants dropped out of the study (one started supplementation with calcium and the other started exercise) (Figure). Six months of intervention allowed for 78 sessions. The number of participant absences did not differ significantly between the experimental groups (P = .558), and the variation was from 0 to 17 (6.8 ± 5.7) for the VG and 0 to 14 (5.8 ± 4.1) for the PG. Thus, the mean frequency in the 2 groups was 91.3% and 92.6%, respectively (Supplementary Table 3, Supplemental Digital Content, available at: http://links.lww.com/JGPT/A218).

Figure.
Figure.:
Flow diagram (CONSORT) throughout the course of the study. ITT indicates intention-to-treat.

Baseline and Bone Outcomes

Table 1 lists the age, anthropometric parameters, menopausal time, and conditions related to BMD and DXA values of the 3 groups at baseline. No significant differences were observed between the groups for any baseline parameter. Table 2 lists the DXA values of the lumbar spine, femoral neck, total hip, trochanter, intertrochanter, and ward's area at baseline and follow-up, for intragroup changes and between-group interaction. The experimental groups (VG and PG) significantly (P ≤ .001) improved DXA values of the intragroup of the lumbar spine and trochanter, but no other measurements of aBMD. For the lumbar spine and trochanter, a significant (P ≤ .004) difference was observed between groups at follow-up. In this case, the multiple comparisons in pairs presented in Supplementary Table 4 (Supplemental Digital Content, available at: http://links.lww.com/JGPT/A19) show that the VG and the PG obtained a significant (P ≤ .018) improvement in DXA values of the lumbar spine and trochanter, when compared with the CG: VG versus CG, for the aBMD of the lumbar spine (0.014 g/cm2; 95% confidence interval (CI), 0.006-0.022; P = .018, d = 1.21) and trochanter (0.018 g/cm2; 95% CI, 0.006-0.030; P = .012, d = 1.03); PG versus CG, for the aBMD of the lumbar spine (0.016 g/cm2; 95% CI, 0.007-0.025; P = .008, d = 1.15) and trochanter (0.020 g/cm2; 95% CI, 0.010-0.031; P = .005, d = 1.28). The post hoc analysis did not reveal any statistical difference between VG and PG.

Table 1. - Baseline Characteristics of the Participants
Variable All (n = 51) Vibration Group (n = 17) Pilates Group (n = 17) Control Group (n = 17) F P Valuea
Age, mean (SD), y 55.4 (6.2) 56.4 (6.5) 55.6 (6.8) 54.1 (5.3) 0.567 .571
Weight, mean (SD), kg 65.5 (7.2) 64.4 (6.3) 67.4 (8.6) 64.6 (6.6) 0.921 .405
Height, mean (SD), cm 156.8 (5.7) 156.3 (4.5) 157.2 (5.9) 153.8 (4.3) 1.721 .190
BMI, mean (SD), kg/m2 26.9 (2.6) 26.2 (2.6) 27.2 (2.7) 27.3 (2.5) 0.907 .410
Time since menopause, mean(SD), y 8.8 (6.4) 8.8 (5.1) 8.4 (7.1) 9.1 (7.0) 1.374 .503b
Condition regarding BMD, n (%)
No alterations 10 (19.6) 3 (5.9) 4 (7.8) 3 (5.9) 2.439 .656c
Osteopenic 31 (60.8) 11 (21.6) 8 (15.7) 12 (23.5)
Osteoporotic 10 (19.6) 3 (5.9) 5 (9.8) 2 (3.9)
DXA areal BMD measurement, mean (SD), g/cm2
Lumbar spine (L1-L4) 0.94 (0.13) 0.96 (0.11) 0.93 (0.18) 0.99 (0.09) 0.307 .737
Femoral neck 0.76 (0.11) 0.77 (0.11) 0.76 (0.13) 0.75 (0.08) 0.096 .909
Total hip 0.89 (0.09) 0.90 (0.09) 0.88 (0.11) 0.89 (0.08) 0.138 .872
Trochanter 0.60 (0.08) 0.61 (0.08) 0.60 (0.09) 0.60 (0.07) 0.096 .909
Intertrochanter 1.04 (0.11) 1.06 (0.10) 1.03 (0.14) 1.04 (0.09) 0.210 .811
Ward's area 0.53 (0.13) 0.54 (0.15) 0.50 (0.12) 0.54 (0.11) 0.545 .583
Abbreviations: BMD, bone mineral density; BMI, body mass index; DXA, dual-energy x-ray absorptiometry; SD, standard deviation.
aAnalysis of variance 1 way.
bKruskal-Wallis test.
cPearson χ2.

Table 2. - Intragroup and Between-Group Comparisons for Dual-Energy X-Ray Absorptiometry Values of Areal Bone Mineral Density Measurement (g/cm2), Between Baseline And Follow-upa
Value Vibration Group (n = 17) Pilates Group (n = 17) Control Group (n = 17) F P Valueb
Lumbar spine (L1-L4)
Baseline 0.96 (0.11) 0.93 (0.18) 0.94 (0.09) 6.209 .004
6 mo 0.98 (0.11) 0.94 (0.19) 0.94 (0.09)
Change 0.02 (0.01)c 0.02 (0.02)c 0.00 (0.01)
P valued 0.00 0.00 0.53
Cohen's d 1.18 1.03 0.10
Femoral neck
Baseline 0.77 (0.11) 0.76 (0.13) 0.75 (0.08) 0.394 .677
6 mo 0.78 (0.10) 0.77 (0.12) 0.75 (0.08)
Change 0.01 (0.04) 0.09 (0.05) 0.00 (0.03)
P valued 0.14 0.51 0.63
Cohen's d 0.36 0.16 0.11
Total hip
Baseline 0.90 (0.09) 0.88 (0.11) 0.89 (0.08) 1.409 .255
6 mo 0.91 (0.10) 0.90 (0.11) 0.89 (0.08)
Change 0.01 (0.02) 0.02 (0.03) 0.02 (0.01)
P valued 0.24 0.05 0.69
Cohen's d 0.29 0.51 0.17
Trochanter
Baseline 0.61 (0.08) 0.60 (0.10) 0.60 (0.07) 6.768 .003
6 mo 0.63 (0.08) 0.62 (0.10) 0.61 (0.06)
Change 0.02 (0.02)c 0.02 (0.01)c 0.00 (0.02)
P valued 0.00 0.00 0.80
Cohen's d 1.01 1.48 0.06
Intertrochanter
Baseline 1.06 (0.10) 1.03 (0.14) 1.04 (0.09) 0.665 .519
6 mo 1.06 (0.11) 1.04 (0.13) 1.04 (0.09)
Change 0.01 (0.02) 0.01 (0.04) −0.00 (0.02)
P valued 0.39 0.27 0.87
Cohen's d 0.23 0.26 0.04
Ward's area
Baseline 0.54 (0.15) 0.50 (0.12) 0.54 (0.11) 0.541 .586
6 mo 0.55 (0.14) 0.52 (0.13) 0.53 (0.12)
Change 0.01 (0.04) 0.02 (0.06) −0.00 (0.04)
P valued 0.54 0.24 0.92
Cohen's d 0.16 0.30 0.02
aOutcome values at each time point are mean (standard deviation).
bBetween-group comparison (analysis of covariance adjusted for baseline outcomes).
cSignificantly different (P < .05) from the control group (post hoc Bonferroni test).
dIntragroup comparison (t test for dependent samples).

Adverse Events

Serious adverse events were reported in all the 3 groups: 2 falls in the VG; 2 falls in the PG; and 1 fall in the CG that led to a fractured wrist. Reports of pain occurred mainly in the VG and the PG. The principal complaint of the participants was delayed muscle soreness, provided by WBV (58.8%) and Pilates (100%), principally in the first weeks of intervention. Other less serious adverse events, such as pain in specific body regions, muscle spasms, and cramps, occurred less frequently (Supplementary Table 5, Supplemental Digital Content, available at: http://links.lww.com/JGPT/A20).

DISCUSSION

Summary of the Main Results

The results demonstrated that WBV or Pilates administered for 6 months, 3 times a week, were equally effective for significant improvement of BMD in the lumbar spine and trochanter in postmenopausal women but not for other bone regions. Both intervention techniques were superior to no therapy. It is noteworthy that only 2 CG participants abandoned the study, resulting in a follow-up of 96.1% of the participants initially randomized. In addition, other relevant information is that the average frequency of the participants submitted to the interventions (VG and PG) was higher than 90%. Serious adverse events (mainly falls) occurred in 9.8% of all participants and affected all 3 groups.

Effects of Whole-Body Vibration on BMD

With regard to WBV, the mechanism by which vibration increases BMD is not fully understood. One hypothesis is that the skeletal responses to WBV tend to be similar to those of exercise, by the mechanotransduction process, in which the mechanical stimulation applied to the bone is detected by cells that generate biochemical signals, stimulating the osteogenesis.27 In a previous systematic review and meta-analysis of RCTs, our research group already noted that the lumbar spine and trochanter regions may be the most responsive to increases in BMD in postmenopausal women. However, significant results were only observed in subgroup analyses, when parameters potentially more suitable for WBV were used, such as side-alternating vibration, knee semiflexion, low frequency, and high magnitude. Subgroup analyses that evaluated these parameters demonstrated effects on the lumbar spine BMD between 0.010 and 0.016 g/cm2, while for the trochanter the variation was 0.019 to 0.020 g/cm2,8 close to the values found in the present study. Compared with the CG, participants in the VG demonstrated an increase in the BMD of 0.014 and 0.018 g/cm2 for the lumbar spine and trochanter, respectively. In addition, for the 2 variables, a large effect size (Cohen's d > 0.80) was observed.

Iwamoto et al28 and Gusi et al29 also using low-frequency, high-magnitude, semiflexed knee and side-alternating type vibration found significant improvements for the BMD of the lumbar spine and femoral neck regions, respectively. However, following these same parameters, Liphardt et al30 evaluating the regions of the lumbar spine and femoral neck and Beck and Norling31 evaluating the proximal forearm did not find significant improvements in BMD. As WBV allows different parameters, the greatest controversy concerns which parameters enable greater osteogenesis. For example, the fact that all studies with postmenopausal women performed so far using high frequency and low magnitude have not found significant results for BMD in any of the bone regions draws attention,31–35 although Rubin et al33 found significant improvements in lumbar spine BMD, when they considered lighter women (<65 kg) and were in the highest compliance quartile. This premise refutes Wolff's bone remodeling law in which there is a need for high impact (great magnitude) to enable greater osteogenic effect.36 The use of these parameters (high frequency and low magnitude) is typically justified in the different studies because they have been successfully tested in animal models37–39; however, they do not appear to enable the same effects in postmenopausal women.

Another important fact is that all the studies that tested synchronous vibration also did not find any significant results for different BMD regions, regardless of frequency and magnitude.32–35,40–42 In addition, Von Stengel et al42 compared 2 types of vibration (synchronous and side-alternating) and verified that only the group of postmenopausal women submitted to side-alternating vibration significantly improved lumbar spine BMD when compared with the control group. The basic difference between vibration types is that the synchronous platforms cause the right and left feet to move up and down at the same time, while on the side-alternating platforms oscillations occur around a pivot in the center of the platform, exposing the user to alternating vibrations between the sides (while the right foot moves up, the left foot moves down and vice versa),43 which supposedly alters the osteogenic effect during WBV.

Regarding body positioning, studies that used knees extended during WBV generally did not find significant improvements in BMD of any bone region,31–35 with the exception of the study of Lai et al,18 in which significant effects for lumbar spine BMD were observed. This can be justified by the type of vibration; while this study18 used side-alternating vibration, the others predominantly used synchronous vibration.32–35 Supposedly, positioning with the knees extended allows greater dissipation of the vibration by the skeleton; however, it has been demonstrated that at frequencies of up to 30 Hz the damping of the vibrations in the position of semiflexed knees is insignificant for the regions of the lumbar spine and femur.44 Similarly, Harazin and Grzesik45 found that, at frequencies above 25 Hz, 50% of the variability in the transmissibility of vibration by body segments is justified by body positioning. The authors identified the hip, trunk, and head regions are the ones losing higher transmissivity at higher frequencies, particularly with flexed knees, since the propagation of vibration occurs through the joints.

Thus, although there is a need for further research taking into account the arguments presented here, the parameters chosen for WBV training in the present study seem to contribute more effectively to the increase of BMD in postmenopausal women than other parameters tested to date.

Effects of Pilates on BMD

To date, only 1 RCT has investigated the effects of Pilates exercise on BMD in postmenopausal women. Angin et al17 demonstrated that 6 months of Pilates performed 3 times a week prompted a significant increase in lumbar spine BMD, with great osteogenic effect (0.063 g/cm2), while other body regions were not investigated. Perhaps the large effect found by the authors when comparing Pilates to no intervention can be justified by the fact that they only included participants with osteoporosis. Studies have shown that less dense bones may demonstrate a greater response to interventions to increase BMD.33,46,47 In the present study, in which participants were included regardless of bone condition (no alterations, osteopenic, and osteoporotic), the osteogenic effect on the lumbar spine BMD was 0.016 g/cm2 in favor of the PG compared with the CG (Cohen's d > 0.80).

A meta-analysis that grouped different forms of intervention using resistance exercises of greater overload and less repetition found a significant increase for the BMD of the lumbar spine (0.86%) and femoral neck (1.03%), but not for other body regions (total hip, trochanter, and ward's area) in postmenopausal women.7 When grouping studies that made use of resistance exercises with lower overload and a greater number of repetitions, no significant results were observed. Although no meta-analysis has addressed Pilates, this form of intervention with resistance exercises uses higher overload and fewer repetitions. Coinciding with the findings of Howe et al,7 the present study showed a significant osteogenic effect for the BMD of the lumbar spine; however, the authors found improvement in the femoral neck, while the present study observed improvement for the trochanter.

The elaboration of the Pilates exercise protocol for the present study was conducted in a way that fostered increased BMD, adequately controlling the intensity of therapy, with a heavy exercise level (Borg CR10: between 5 and 6) maintained during the muscle-strengthening exercises, resulting in increased overload and fewer repetitions. Nevertheless, we attempted to maintain a traditional sequence of the method, which is typically adopted in clinical practice, with stretching at the beginning and end of the sessions. In addition, all muscle-strengthening exercises were performed on equipment, which mostly enabled the use of springs, facilitating the increase of the overload. Melo et al24 demonstrated that the resistance torque provided by the springs during Pilates movements can vary depending on 2 factors (their positioning on the equipment or the level of resistance offered by the springs). The resistance torque also changes during the execution of the movement as the spring lengthens, offering different stresses during the same movement—factors that were considered in the prescription and evolution of Pilates intervention protocol in the present study, allowing adequate overload. These parameters are important for outcomes such as BMD, which requires greater overload and fewer repetitions.7

Regarding the possibilities of exercises aimed at muscle strengthening, as a means of prevention and assistance in the treatment of osteoporosis, a committee of specialists of the National Osteoporosis Foundation recommended conventional training with the use of weights, as well as Pilates and yoga.10 However, just like Pilates, yoga exercises lack support from RCTs demonstrating their effects on BMD in postmenopausal women. Some uncontrolled clinical trials have demonstrated that the practice may be effective in increasing bone mass in postmenopausal women48 or older adults.49

It is worth considering that, in muscle-strengthening exercises, the exact mechanism by which mechanical stimulation is converted into anabolic or catabolic signaling (mechanotransduction) into the bone tissue remains to be completely determined. The bone mass is largely regulated by mechanical forces derived from skeletal muscle; thus, changes in strength and muscle mass provided by the regular and systematic practice of overloading exercises may contribute to the mechanical loading of the bone.50 Another aspect concerns endocrine changes provided by exercise, which point to anabolic effects on bone tissue during exercise and recovery phases.51

Strengths and Limitations

This is the first RCT to compare the effects of WBV with Pilates on the BMD in postmenopausal women. Since the parameters chosen for WBV vary widely in different studies, in the present research we explored those that until now have been identified as providing greater osteogenic effects.8 On the other hand, in relation to Pilates, there has only been 1 RCT performed with postmenopausal women to verify the effects on BMD, but without exploring different bone regions.17 In the present study, we explored 6 different bone regions, which made it possible to identify the areas most responsive to osteogenesis. As a limitation, since the intervention involved WBV and Pilates, it was not possible to blind the randomized participants in the 3 groups and the physiotherapists who administered the therapies. However, it is unlikely that this limitation influenced the bone outcomes investigated.

CONCLUSION

The WBV and Pilates techniques administered 3 times a week over 6 months provided the same effect on the BMD in postmenopausal women. Both were superior to no intervention on the bone regions of the lumbar spine and trochanter. Since the techniques are relatively safe and offer the same osteogenic effect, the choice of which to use can take into account the existing resources or patients' preferences. In addition, as there is no conclusive evidence on the best parameters of WBV or Pilates, based on multiple RCTs of good size, concordant and/or robust meta-analysis of RCTs, the parameters presented in the present study can be used as a reference in future interventions.

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Keywords:

aging; exercise therapy; osteopenia; osteoporosis; rehabilitation

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