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Abstract

BACKGROUND:

Interventions using Pilates and whole body vibration (WBV) have been conducted in postmenopausal women, aimed at increasing muscular strength and quality of life; however, some results are contradictory.

OBJECTIVE:

To compare the effects of Pilates vs. WBV on isokinetic muscle strength and quality of life in postmenopausal women.

METHODS:

Fifty-one (51) women were randomly assigned to the following groups, Pilates ( $n=$ 17), vibration ( $n=$ 17), or control ( $n=$ 17). Evaluations were performed for isokinetic muscular strength (N.m) of knee extensors and flexors (60 ${}^{\circ}$ /s and 180 ${}^{\circ}$ /s) and quality of life using the SF-36. The interventions were performed three times a week for six months, totaling 78 sessions. Analyzes for the primary outcomes were performed with intention-to-treat and covariance analyses adjusted for baseline outcomes.

RESULTS:

96.1% of participants completed the follow-up. The Pilates was superior ( $p<$ 0.05) to WBV for muscle strength of the knee flexors at 60 ${}^{\circ}$ /s (% Change: 16.71 $\pm$ 20.68 vs. 6.18 $\pm$ 19.42; Cohen’s $d=$ 0.70) and superior ( $p<$ 0.05) to the control group in all muscular strength variables and in four SF-36 domains.

CONCLUSIONS:

Pilates is an alternative intervention superior to WBV when the goal is linked to the strength of the knee flexor muscles.

Keywords

Exercise isokinetic muscular strength menopause women’s health

1. Introduction

Women experience hormonal alterations in the postmenopausal period due to the rapid decline in estrogen levels [1]. In this period, the ovulatory cycle ceases, coinciding with important physiological alterations typical of the aging process [2], which potentiates the appearance of negative effects on health, such as a decrease in muscular strength [3] and impaired quality of life [4].

Among the ways to mitigate or reverse these factors, we highlight the regular and systematic practice of physical exercises [5]. An emerging exercise option that has been investigated in relation to its benefits for postmenopausal women is the Pilates exercise [6, 7]. This technique works through progressive muscular endurance exercises and has been shown to be effective for increasing muscular strength [8, 9, 10, 11, 12, 13, 14, 15] and improving quality of life in older women [7, 15, 16, 17]. A meta-analysis study of the effects of Pilates on different health outcomes in older adults, identified that the method promotes significant improvement in muscular strength and quality of life [18]. However, other studies have shown that Pilates may not increase muscular strength [19] or contribute to improvement in different domains of quality of life in older adults [20]. These conflicting data may be related to the duration of intervention [19], or the absence of a control group [20], which compromises the level of evidence.

Another technique that has demonstrated different benefits for health outcomes in women during the postmenopausal period is whole body vibration (WBV) [21, 22]. Studies have shown that WBV may increased muscular strength [23, 24, 25] and improved quality of life in older adults [26, 27], however, some studies did not observe benefits of this technique on muscular strength [28, 29] or quality of life [30]. A systematic review and meta-analysis [22] concluded that WBV provides significant effects on dynamic knee extension strength and isometric leg extension strength in older adults when compared to no intervention but no differences when compared to other physical exercise modalities. However, WBV did not increase isometric knee extension strength when compared to no intervention or other forms of exercise [22].

Unlike conventional modalities of physical exercise, in WBV the individual remains standing on an oscillatory plate, which transmits mechanical vibrations throughout the body [31]. Several studies have compared WBV with different forms of physical exercise interventions on variables related to muscular strength [25, 32, 33, 34, 35]. In the majority of these studies, WBV was not found to be significantly different from conventional exercises that provide muscular strengthening when taking into consideration the peak isokinetic torque of knee extensors [25, 32, 35], and may be more effective in increasing the strength of the ankle flexors [34], or less effective when considering the strength of the upper limbs [33].

A controversy in the interventions involving WBV is the different parameters that can be used to modify the intensity of the vibrations, such as frequency, magnitude, and time of exposure [31]. Furthermore, the majority of studies performed up to now have prescribed strengthening exercises for the lower limbs during WBV [24, 25, 33, 34, 35, 36, 37], which raises doubts as to whether the effects on muscular strength were due to the mechanical vibrations or performance of muscular strengthening exercises. In addition, the low quality of evidence limits confidence in reported observations.

No studies have been found that compared Pilates and WBV, and there are few studies of good methodological quality that compare these modalities with no intervention. Therefore, the objective of this study was to examine the effects of six months of Pilates exercise compared to WBV and no treatment controls on the peak isokinetic torque of the extensor and flexor muscles of the knee in postmenopausal women. As a secondary objective, we sought to identify the effects of the techniques on the quality of life of this population.

2. Method

This study was a randomized controlled clinical trial (registered at www.clinicaltrials.gov on May 7, 2016: NCT02769143), which followed the CONSORT recommendations. The intervention lasted six months and involved 51 postmenopausal women (who had experienced menopause for at least one year), subdivided into three equally sized groups. All the participants were able to practice physical exercise, were aged between 40 and 70 years, and lived in the city of Jacarezinho, state of Paraná, Brazil. The present study followed the ethical norms established by the Declaration of Helsinki (1975, revised in 1983) and was approved by the Human Ethics Committee of the Northern University of Paraná, Brazil (opinion 1,032,182). All participants signed a Free and Informed Consent Term.

2.1 Recruitment and participants

Participants were recruited in May 2016 through posters made available in public places, newspaper adverts, the radio, internet news sites, and leaflets left in medical clinics and health facilities, all with local coverage. The sample calculation was performed in the Bioestat 5.3 program (Mamirauá Institute, Amazonas, Brazil), taking into account the values of isokinetic muscle strength (Nm.) of the knee extensors, at the angular velocity of 60 ${}^{\circ}$ /s, available from a previous study [8]. In this case, the post-intervention mean and standard deviation between the Pilates group (101.1 $\pm$ 14.1) and control group (81.9 $\pm$ 19.6) were used, with a test power of 80% and alpha value of 0.05, which generated the need for at least 13 participants in each group.

The inclusion criteria were a) post-menopausal, clinically confirmed, for at least 12 months; b) not practicing physical exercise for at least six months; c) agreement not to practice another type of exercise during the research; d) ability to perform activities of daily living without assistance [38, 39]; e) presentation of a medical release indicating fitness for exercise; and f) score $\geqslant$ 19 in the Mini-Mental State Examination [40].

The exclusion criteria were a) musculoskeletal dysfunctions in the spine or lower limbs in the previous six months; b) fracture in the vertebral column or in 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 five 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 six 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 bone mineral density or to increase muscle mass in the previous 12 months; and s) inability to tolerate WBV for five minutes.

All participants included in the present study were instructed to maintain their usual routines, as well as their daily physical activities (e.g., domestic duties, paid work) and nutritional habits. They were also instructed not to take any medication or supplement that could influence muscle mass or bone mass.

2.2 Evaluation of muscular strength

To evaluate the muscular strength of the knee extensors and flexors, an isokinetic dynamometer (Biodex System 4.0, Biodex Medical Systems, Shirley, NY, USA) was used. All procedures were performed by an independent evaluator, not directly involved in the research project, experienced in isokinetic evaluations, and blind in relation to the allocation of participants in each group. The equipment was calibrated prior to the test according to the manufacturer’s standards. Preceding the test, the participants performed a five-minute warm-up on a vertical exercise bike, using a light load (25 watts) and comfortable speed (50 rotations per minute). Subsequently, the evaluator positioned the participant in the equipment, with the hip joint making an angle of 120 ${}^{\circ}$ of flexion.

The axis of rotation of the dynamometer arm was aligned with the lateral epicondyle of the femur of the dominant lower limb. The site of force application was positioned approximately two centimeters from the medial malleolus. Belts were attached to the trunk, pelvis and thigh to avoid compensatory movements [41]. After brief familiarization with the equipment and range of motion, the participants performed the knee extension and flexion movements (concentric/concentric) at the angular velocity of 60 degrees per second (60 ${}^{\circ}$ /s), starting with the knee position in 90 degrees of flexion. Three series of five repetitions were performed, with a 30 second interval between series [42]. Next, the same protocol was used for an angular velocity of 180 degrees per second (180 ${}^{\circ}$ /s). Participants were instructed to perform maximal force of voluntary contraction of the knee extensor muscles, followed immediately by maximal contraction of the knee flexor muscles, continuously. During the execution of the test the words of encouragement “more strength” were used in a standardized way. The variable considered for analysis was the peak isokinetic torque, expressed in newtons per meter (Nm.).

2.3 Evaluation of quality of life

To evaluate the quality of life, the Brazilian version of the SF-36 questionnaire was used [43]. This questionnaire consists of 11 questions and 36 items, subdivided into eight components (domains), represented by physical functioning (10 items), role-physical (four items), bodily pain (two items), general health (five items), vitality (four items), social functioning (two items), role-emotional (three items) and mental health (five items). The first four domains assess physical health, while the last four assess mental health. Participants receive a score for each domain, ranging from 0 to 100, with 0 being the worst score and 100 being the best [44]. The questionnaire was applied by an evaluator not directly involved with the study and blinded in relation to the allocation of the participants in each group.

Table 1
Pilates exercise – Protocol 1 and 2

Sequence of the exercises	Equipment	Traditional name of the movements
Protocol 1
Initial stretching	Chair	1) Side Arm Sit; 2) Stretches the Gluteus; 3) Hamstring Stretch
Strengthening of the lower limbs	Wall Unit and Cadillac	4) Leg Series Supine: Lowers; 5) Leg Series Supine: Scissors; 6) Leg Circles; 7) Tower; 8) Tower One Leg; 9) Tower Strengthening the Achilles Tendon
Strengthening of the extensor and lateral flexor muscles of the trunk	Ladder Barrel	10) Swan Dive; 11) Stomach Jumps; 12) Side Sit Ups
Strengthening of the flexor and lateral flexor muscles of the trunk	Spine Corrector	13) Body Up and Down; 14) Balance; 15) Side Sit Ups
Strengthening of the upper limbs	Reformer	16) Arm Pulling; 17) Arm Biceps; 18) Arm Triceps
Final stretching	Ball	19) Lumbar Stretch; 20) Stretching of the Posterior Chain; 21) Stretching the Side Chain
Protocol 2
Initial stretching	Ladder Barrel	1) Stretches to the Side; 2) Stretches the Gluteus; 3) Stretches Front
Strengthening of the lower limbs	Reformer and Chair	4) Leg Lowers; 5) Leg Lowers and Opening; 6) Leg Circles; 7) Forward Lunge; 8) Pump One Leg Front; 9) Achilles Stretch
Strengthening of the extensor and lateral flexor muscles of the trunk	Small Barrel	10) Swan; 11) Swimming; 12) Side Sit Ups
Strengthening of the flexor muscles of the trunk	Cadillac	13) The Hundred; 14) Teaser; 15) Teaser Side
Strengthening of the upper limbs	Wall Unit	16) Arm Pulling; 17) Arm Biceps; 18) Arm Triceps
Final stretching	Ball	19) Relax; 20) Spine Stretch Forward; 21) Mermaid

2.4 Randomization

After the evaluation of muscular strength and quality of life, participants were randomized to three groups by a researcher who was not part of the study team. The random numbers were generated by software (randomization.com), which distributed the participants to either Pilates group (PG), Vibration group (VG) or Control group (CG), with 17 participants in each. The researcher who performed the randomization sealed the opaque envelopes containing group allocation details and gave them to the principal investigator who was blind to group allocation. The participants, in a blinded manner, individually received the envelopes containing their name. After breaking the envelope seal, the participant and principal investigator checked group allocation.

2.5 Intervention

The interventions occurred three times a week, on nonconsecutive days, for six months (78 sessions), starting in June 2016, in a private clinic located in the city of Jacarezinho, Paraná, Brazil. The experimental groups (PG and VG) were supervised by two professionals with experience in Pilates and WBV. As the intervention included physical exercise, it was not possible to blind the participants or the professionals responsible for the interventions.

2.5.1 Pilates group

The first session of the PG was used to familiarize the participants with the technique, providing an explanation of the correct execution of each movement and 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 (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 the six months of intervention, each performed for three months (Table 1), maintaining the same sequence of strengthening and stretching, as well as the same body segments but changing the order of equipment. Each session lasted 60 minutes.

Figure 1.

Flow diagram (CONSORT) throughout the course of the study. Abbreviation: ITT, Intention-to-treat.

All exercises were performed in a series of ten repetitions, with a one-minute rest interval between exercises. The intensity of the overload in Pilates is mainly determined by the use of springs, which were modified according to the evolution of strength of each participant (changing the position of the springs in the equipment or changing the spring to another one of greater resistance) [45], always maintaining the number of repetitions and series. To determine the level of effort of the participants and the consequent evolution of the overload, a verbal description according to the Borg CR10 scale was used: light load (Borg $\leqslant$ 2), moderate load (Borg $>$ 2 and $<$ 5), heavy load (Borg $\geqslant$ 5 and $<$ 7) and load close to maximum (Borg $\geqslant$ 7) [46]. 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 was immediately annotated on an individual chart used to record the training.

2.5.2 Vibration group

The VG was exposed to WBV for five minutes on a side-alternating type vibratory platform (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) and a peak-to-peak displacement of 4 mm (with reference to the second toe) were used, resulting in a magnitude of 31.5 m/s ${}^{2}$ or 3.2 g (gravity: 1 g $=$ 9.8 m/s ${}^{2}$ ). Participants were instructed to stand on the platform oscillation plate with their knees semi-flexed at 30 degrees and their bare feet spaced at a distance of 50 cm, keeping the torso erect and holding the platform support with both hands. No accessories (such as ethylene vinyl acetate [EVA]) were placed on the platform oscillating plate to cushion the impacts. All parameters used in the equipment and positioning of the participants were maintained throughout the six months of intervention. A slip test ensured that the participants’ feet always remained in contact with the oscillating plate during the WBV [31].

Exposure time was 5 minutes because the side-alternating platform generates a large amplitude peak-to-peak displacement, which does not allow prolonged exposure. Other studies that used an side-alternating platform to identify effects on muscle strength also uses similar of low exposure times [26, 28, 29, 34].

2.5.3 Control group

The CG did not perform any type of intervention. The researcher responsible for the study contacted the CG participants every month during the intervention to emphasize the importance of maintaining their usual routine related to physical activity, eating habits, the importance of not using supplements or medications that could affect bone or muscle mass, and not starting any type of physical exercise, according to the procedure also adopted with the PG and VG. At this time, the participants were also questioned about possible adverse events.

Table 2
Baseline characteristics of participants

	All		Pilates		Vibration		Control		F	P
	( $n=$ 51)		group		group		group			Value ${}^{*}$
			( $n=$ 17)		( $n=$ 17)		( $n=$ 17)
Age (years), mean (SD)	55.3	(6.1)	55.5	(6.8)	56.3	(6.4)	54.1	(5.2)	0.567	0.571
Weight (kg), mean (SD)	65.4	(7.2)	67.4	(8.6)	64.4	(6.2)	64.5	(6.5)	0.921	0.405
Height (cm), mean (SD)	155.7	(5.7)	157.2	(5.8)	156.2	(4.4)	153.7	(4.3)	1.721	0.190
BMI (kg/m ${}^{2}$ ), mean (SD)	26.9	(2.5)	27.2	(2.7)	26.2	(2.5)	27.3	(2.4)	0.907	0.410
Time since menopause (years), median (IQR) ${}^{\dagger}$	6	(4–13)	6	(3–14)	7	(6–12)	7	(5–14)	1.374	0.503
Isokinetic muscular strength (Nm.), mean (SD)
Knee extensors 60 ${}^{\circ}$ /s	95.3	(21.5)	103.5	(24.6)	85.8	(17.8)	96.5	(18.9)	3.139	0.052
Knee flexors 60 ${}^{\circ}$ /s	49.1	(13.5)	51.1	(15.6)	46.5	(14.4)	49.7	(10.4)	0.493	0.614
Knee extensors 180 ${}^{\circ}$ /s	56.4	(11.3)	61.2	(11.8)	51.4	(10.9)	56.5	(9.4)	3.537	0.037
Knee flexors 180 ${}^{\circ}$ /s	35.9	(8.0)	36.5	(9.7)	34.4	(7.6)	36.9	(6.5)	0.471	0.627
Quality of life (SF-36 score), median (IQR) ${}^{\dagger}$
Physical functioning	85	(70–90)	85	(75–95)	85	(65–88)	85	(65–90)	0.732	0.694
Role-physical	100	(75–100)	100	(88–100)	100	(25–100)	100	(38–100)	2.409	0.300
Bodily pain	62	(51–84)	62	(51–92)	72	(51–79)	62	(52–92)	0.065	0.968
General health	82	(65–92)	82	(75–90)	82	(66–94)	77	(47–92)	0.577	0.749
Vitality	70	(50–80)	75	(60–83)	70	(50–80)	70	(50–83)	0.325	0.850
Social functioning	88	(63–100)	75	(75–100)	88	(57–100)	88	(69–100)	0.600	0.741
Role-emotional	100	(33–100)	100	(33–100)	100	(17–100)	67	(33–100)	0.317	0.853
Mental health	72	(64–80)	76	(66–86)	68	(46–80)	76	(64–80)	1.086	0.581

Abbreviations: SD, standard deviation; IQR, interquartile range (25 ${}^{\text{th}}$ –75 ${}^{\text{th}}$ percentiles); BMI, body mass index. ${}^{*}$ Analysis of variance (ANOVA) one way, except for ${}^{\dagger}$ Kruskal-Wallis test for the time since menopause and quality of life.

2.6 Adverse events

A standardized form was used to record occurrences of adverse events in all three groups. Participants were asked every month about any complications such as spasms or muscle pains, joint pains, dizziness, falls, cramps, and changes in blood pressure.

Table 3
Between group comparisons for isokinetic muscular strength (in Nm) between baseline and follow-up

	Pilates group ( $n=$ 17)		Vibration group ( $n=$ 17)		Control group ( $n=$ 17)		F	P value ${}^{\ddagger}$
Knee extensors 60 ${}^{\circ}$ /s
Baseline	103.5	(24.6)	85.8	(17.8)	96.5	(18.9)	4.449	0.017
6 months	110.0	(20.0)	89.2	(15.7)	95.4	(21.8)
Absolute change	6.5	(9.5) ${}^{\text{a}}$	3.4	(7.6)	$-$ 1.1	(10.1)
Knee flexors 60 ${}^{\circ}$ /s
Baseline	51.1	(15.6)	46.5	(14.4)	49.7	(10.4)	5.895	0.005
6 months	57.5	(12.4)	47.7	(10.7)	50.7	(11.4)
Absolute change	6.4	(6.8) ${}^{\text{a},\text{b}}$	1.2	(8.0)	1.0	(5.8)
Knee extensors 180 ${}^{\circ}$ /s
Baseline	61.2	(11.8)	51.4	(10.9)	56.5	(9.4)	3.683	0.033
6 months	65.2	(11.0)	54.5	(10.2)	55.9	(10.0)
Absolute change	4.0	(5.5) ${}^{\text{a}}$	3.1	(7.2)	$-$ 0.6	(5.7)
Knee flexors 180 ${}^{\circ}$ /s
Baseline	36.5	(9.7)	34.4	(7.6)	36.9	(6.5)	4.781	0.013
6 months	40.6	(11.3)	35.5	(7.8)	36.9	(7.5)
Absolute change	4.1	(2.6) ${}^{\text{a}}$	1.1	(3.2)	0.0	(5.4)

Outcome values at each time point are mean (standard deviation). ${}^{\ddagger}$ Between-group comparison (ANCOVA adjusted for baseline outcomes), with Post Hoc Bonferroni test: ${}^{\text{a}}$ Significantly different from the Control group ( $p<$ 0.05); ${}^{\text{b}}$ Significantly different from the Vibration group ( $p<$ 0.05).

Table 4

Comparisons of pairs for isokinetic muscular strength (in Nm)

Change between baseline and follow-up, mean (SD)					Mean difference (95% CI) between-group		P value ${}^{*}$	Cohen’s d
Knee extensors 60 ${}^{\circ}$ /s
Pilates group	6.5 (9.5)	Vibration group	3.4	(7.6)	3.1	( $-$ 2.6, 8.8)	0.188	0.37
Pilates group	6.5 (9.5)	Control group	$-$ 1.1	(10.1)	7.6	(1.0, 14.1)	0.015	0.78
Vibration group	3.4 (7.6)	Control group	$-$ 1.1	(10.1)	4.5	( $-$ 1.5, 10.5)	1.000	0.50
Knee flexors 60 ${}^{\circ}$ /s
Pilates group	6.4 (6.8)	Vibration group	1.2	(8.0)	5.2	(0.2, 10.1)	0.009	0.70
Pilates group	6.4 (6.8)	Control group	1.0	(5.8)	5.4	(1.1, 9.6)	0.024	0.83
Vibration group	1.2 (8.0)	Control group	1.0	(5.8)	0.2	( $-$ 4.5, 4.9)	1.000	0.01
Knee extensors 180 ${}^{\circ}$ /s
Pilates group	4.0 (5.5)	Vibration group	3.1	(7.2)	0.9	( $-$ 3.4, 5.2)	0.584	0.13
Pilates group	4.0 (5.5)	Control group	$-$ 0.6	(5.7)	4.6	(0.8, 8.3)	0.028	0.82
Vibration group	3.1 (7.2)	Control group	$-$ 0.6	(5.7)	3.7	( $-$ 0.6, 8.0)	0.579	0.57
Knee flexors 180 ${}^{\circ}$ /s
Pilates group	4.1 (2.6)	Vibration group	1.1	(3.2)	3.0	(1.0, 4.9)	0.113	1.00
Pilates group	4.1 (2.6)	Control group	0.0	(5.4)	4.1	(1.2, 6.9)	0.013	0.96
Vibration group	1.1 (3.2)	Control group	0.0	(5.4)	1.1	( $-$ 1.8, 4.0)	1.000	0.25

Abbreviations: SD, standard deviation; 95% CI, 95% confidence interval. ${}^{*}$ Multiple comparisons (Post Hoc Bonferroni test).

Table 5

Between-group comparisons for quality of life (SF-36 score), between baseline and follow-up

	Pilates group ( $n=$ 17)		Vibration group ( $n=$ 17)		Control group ( $n=$ 17)		F	P value ${}^{\ddagger}$
Physical functioning
Baseline	85	(75–95)	85	(65–88)	85	(65–90)
6 months	95	(78–95)	85	(68–90)	85	(65–90)	4.800	0.091
Role-physical
Baseline	100	(88–100)	100	(25–100)	100	(38–100)
6 months	100	(100–100) ${}^{\text{a}}$	100	(38–100)	75	(75–100)	6.756	0.034
Bodily pain
Baseline	62	(51–92)	72	(51–79)	62	(52–92)
6 months	82	(62–100) ${}^{\text{a}}$	74	(62–85)	61	(22–74)	6.729	0.035
General health
Baseline	82	(75–90)	82	(66–94)	77	(47–92)
6 months	82	(77–92)	92	(85–96)	82	(47–92)	5.687	0.058
Vitality
Baseline	75	(60–83)	70	(50–80)	70	(50–83)
6 months	85	(75–90)	75	(65–93)	70	(55–80)	4.177	0.124
Social functioning
Baseline	75	(75–100)	88	(57–100)	88	(69–100)
6 months	100	(87–100) ${}^{\text{a}}$	88	(63–100)	63	(50–100)	6.964	0.031
Role-emotional
Baseline	100	(33–100)	100	(17–100)	67	(33–100)
6 months	100	(100–100) ${}^{\text{a}}$	100	(33–100)	63	(33–67)	8.649	0.013
Mental health
Baseline	76	(66–86)	68	(46–80)	76	(64–80)
6 months	84	(78–96)	80	(68–90)	72	(52–84)	3.019	0.221

Outcome values at each time point are median (interquartile range, 25 ${}^{\text{th}}$ –75 ${}^{\text{th}}$ percentiles). ${}^{\ddagger}$ Between-group follow-up comparison (Kruskal-Wallis test). ${}^{\text{a}}$ Significantly different from the control group ( $p<$ 0.05).

2.7 Statistical analysis

Parametric data are presented as mean and standard deviation (SD), and non-parametric data as median and the respective interquartile range (25 ${}^{\text{th}}$ and 75 ${}^{\text{th}}$ percentiles). The normality of the data was assessed by the Shapiro-Wilk test. The Student t test for independent samples was used to compare the number of participants’ absences during the interventions (PG vs. VG). The homogeneity of variances was determined by the Levene test. In order to verify whether the three groups presented with pre-intervention differences, one-way ANOVA was used for data with normal distribution (age, weight, height, BMI, and isokinetic muscular strength). Otherwise, the Kruskal-Wallis test (time of menopause and quality of life) was used. To examine differences between groups for isokinetic muscular strength, covariance analysis (ANCOVA) was applied, with the post-intervention data used as dependent variables and the pre-intervention data as adjustment covariates. As a post hoc, the Bonferroni test was used in multiple comparisons between pairs (PG vs. VG, PG vs. CG, and VG vs. CG). For the isokinetic muscular strength variables, the effect sizes between-group were calculated using Cohen’s d, which were considered small (0.20), medium (0.50), or large (0.80) [47]. To examine between-group differences in quality of life after the interventions, the Kruskal-Wallis test was used. Initially, intention-to-treat analysis (ITT) was utilized, including all randomized participants (missing post-intervention data on two CG participants were imputed by the group mean). Subsequently, a per protocol analysis was performed, excluding the two CG participants who dropped out of the study. As the results were similar, only the ITT analysis is presented in the results of this study. For all tests, the level of significance was 95% ( $p<$ 0.05). Analyzes were processed in the SPSS 20.0 program (Chicago, IL, USA), except for effect size calculations (Cohen’s d), which were processed in the GPower 3.1 program (Franz Faul, Universita Ä Kiel, Germany).

3. Results

3.1 Participation

Initially 620 women were interviewed. After applying inclusion/exclusion criteria, 51 volunteers were eligible to participate (17 in each group). Of the 51 participants initially randomized, 49 (96.1%) completed the follow-up. Two CG participants dropped out of the study (one started exercising and the other took calcium-based supplementation) (Fig. 1). There were 78 intervention sessions over the 6 months of the study. The number of participants’ absences did not differ significantly between the experimental groups ( $p=$ 0.558), and ranged from 0 to 14 sessions (5.8 $\pm$ 4.1) for the PG and 0 to 17 (6.8 $\pm$ 5.7) for the VG. The mean attendance frequency in the two groups was 92.6% and 91.3%, respectively.

3.2 Baseline characteristics

Table 2 presents the baseline characteristics of the participants. Age, anthropometric variables, time in menopause, and SF-36 domains were similar in all three groups ( $p>$ 0.05). Among the variables of isokinetic muscular strength, the peak torque at 180 ${}^{\circ}$ /s of the knee extensor muscles was significantly different between groups ( $p=$ 0.037), with the Bonferroni post hoc analysis showing that the PG was superior to the VG ( $p=$ 0.032). For the other isokinetic muscular strength variables, the groups were similar at baseline ( $p>$ 0.05).

3.3 Muscular strength

Table 3 presents the results of isokinetic muscular strength of knee extensors and flexors at 60 ${}^{\circ}$ /s and 180 ${}^{\circ}$ /s between groups. The PG was significantly ( $p<$ 0.05) higher than CG for all variables analyzed, with large effect sizes (Cohen’s $d>$ 0.80), except for the peak isokinetic torque of knee extensors at 60 ${}^{\circ}$ /s, where a moderate effect size (Cohen’s $d=$ 0.78) was observed. In addition, the PG was significantly ( $p<$ 0.05) higher than VG for the peak isokinetic torque of the knee flexors at 60 ${}^{\circ}$ /s, with a moderate effect size (Cohen’s $d=$ 0.70). Table 4 presents details of the post hoc analyses for isokinetic muscular strength.

Table 6
Comparisons of pairs for quality of life (SF-36 score)

Follow-up, median (IQR)						F	P value ${}^{*}$
Role-physical
Pilates group	100	(100–100)	Vibration group	100	(38–100)	1.689	0.274
Pilates group	100	(100–100)	Control group	75	(75–100)	2.546	0.033
Vibration group	100	(38–100)	Control group	75	(75–100)	0.911	1.000
Bodily pain
Pilates group	82	(62–100)	Vibration group	74	(62–85)	0.484	1.000
Pilates group	82	(62–100)	Control group	61	(22–74)	2.525	0.035
Vibration group	74	(62–85)	Control group	61	(22–74)	1.847	0.194
Social functioning
Pilates group	100	(87–100)	Vibration group	88	(63–100)	1.446	0.445
Pilates group	100	(87–100)	Control group	63	(50–100)	2.632	0.025
Vibration group	88	(63–100)	Control group	63	(50–100)	1.232	0.654
Role-emotional
Pilates group	100	(100–100)	Vibration group	100	(33–100)	1.006	0.943
Pilates group	100	(100–100)	Control group	63	(33–67)	2.905	0.011
Vibration group	100	(33–100)	Control group	63	(33–67)	1.931	0.160

Abbreviations: IQR, interquartile range (25 ${}^{\text{th}}$ –75 ${}^{\text{th}}$ percentiles). ${}^{*}$ Multiple comparisons (Post Hoc Dunn test).

3.4 Quality of life

Table 5 presents the results of the quality of life comparisons as measured by the SF-36 questionnaire between groups. The PG was significantly ( $p<$ 0.05) higher than the CG for the domains role-physical, bodily pain, social functioning, and role-emotional. Table 6 presents details of the post hoc analysis for quality of life.

3.5 Adverse events

Serious adverse events were reported in all three groups: two falls in the PG, two in the VG and one fall in the CG (that led to a fractured wrist for CG participant). All falls occurred outside exercise sessions. Reports of pain occurred mainly in the PG and VG. The primary complaint reported by participants was delayed onset muscle soreness, reported by the PG (100%) and VG (58.8%), principally in the first weeks of the intervention. Other less serious adverse events, such as pain in specific regions of the body, muscle spasms, and cramps occurred less frequently (Table 7).

Table 7
Summary of adverse events

	Pilates		Vibration		Control
	group		group		group
	( $n=$ 17)		( $n=$ 17)		( $n=$ 17)
Serious adverse events, n (% within the group)
Falls	2	(11.8)	2	(11.8)	1	(5.8)
Fractures	0	(0.0)	0	(0.0)	1	(5.8)
Pain, n (% within the group)
Delayed onset muscle	17	(100)	10	(58.8)	0	(0.0)
soreness
Muscle pain in the lower	0	(0.0)	0	(0.0)	1	(5.8)
limbs
Pain in the spine	1	(5.8)	3	(17.6)	2	(11.8)
Pain in the knee joint	5	(29.4)	4	(23.5)	3	(17.6)
Pain in the shoulder joint	4	(23.5)	0	(0.0)	0	(0.0)
Pain in the wrist joint	1	(5.8)	0	(0.0)	0	(0.0)
Pain in the soles of the feet	1	(5.8)	4	(23.5)	0	(0.0)
Other, n (% within the group)
Dizziness	2	(11.8)	4	(23.5)	0	(0.0)
Cramp	5	(29.4)	0	(0.0)	0	(0.0)
Muscle spasms	0	(0.0)	1	(5.8)	0	(0.0)
Elevated blood pressure	0	(0.0)	4	(23.5)	0	(0.0)

4. Discussion

4.1 Summary of the main results

This study aimed to examine the effects of Pilates exercise and WBV on the isokinetic muscular strength of knee extensors and flexors and quality of life in postmenopausal women. After six months of intervention, Pilates was superior ( $p<$ 0.05) to WBV only for muscular strength of the knee flexors at 60 ${}^{\circ}$ /s. In the comparisons with the control group, Pilates was superior ( $p<$ 0.05) in all muscular strength variables and in four SF-36 domains. No differences were observed between WBV and control group for muscle strength and quality of life.

4.2 Muscular strength

In agreement with the findings of the present study, others have identified significant improvement in lower limb muscular strength when comparing Pilates exercise in older women to control comparisons who received no treatment [9, 13, 14] or minimal intervention (stretching) [8, 15]. Oliveira et al. [8] evaluated the peak isokinetic torque of knee extensors and flexors at 60 ${}^{\circ}$ /s, while Campos de Oliveira et al. [15] tested the velocity at 300 ${}^{\circ}$ /s. After 12 weeks of Pilates, both studies identified significant improvements. After a 12 week intervention, Vieira et al. [9] observed a significant improvement in the sit-to-stand test, while Plachy et al. [13] identified significant improvement for the same test after six months of a Pilates intervention. Irez et al. [14] also observed a significant improvement in muscular strength of the hip flexors, adductors, and abductors after 12 weeks of Pilates.

In addition, a meta-analysis that grouped the different studies that applied the Pilates exercise as a form of intervention, identified that compared to control outcomes, the technique is associated with a large effect size ( $d=$ 1.23) in the muscular strength of older adults [18]. A single study identified in our search [19] did not identify significant improvements in muscular strength of knee extensors and ankle dorsiflexors in older adults for a maximal repetition test after six weeks of Pilates. It is possible this lack of significant results can be explained by the intervention duration (six weeks). All other studies that identified significant results for muscular strength in older adults performed at least 12 weeks of intervention. Future studies should focus on performing assessments over time to identify the point at which significant effects on muscle strength begin to occur and when they stabilize. It would also be valuable to know how long exercise effects last before muscle strength begin to decline. This information could advance clinical decision making.

Our results indicate that WBV was not effective in increasing the peak isokinetic torque of knee extensors and flexors in comparison with the control group, corroborating reports of investigations into the effects of this technique in postmenopausal women. Liphardt et al. [28] used WBV on a side-alternating platform at 20 Hz, peak-to-peak amplitude of 3 to 4 mm, with participants standing with knee flexion of 30 ${}^{\circ}$ for 10 minutes. After 12 months of intervention, the authors found no significant improvement in isokinetic muscle strength of knee extensors. Raimundo et al. [29] used WBV on a side-alternating platform at 12.6 Hz, peak to peak amplitude of 3 mm, in the knee flexion position at 120 ${}^{\circ}$ , for 3 minutes. After eight months of intervention, no significant results were observed for isokinetic muscular strength of knee extensors at 60 ${}^{\circ}$ /s or 300 ${}^{\circ}$ /s. An exception was the study by Wei et al. [23] who performed synchronous vibration at three different frequencies, 20, 40, and 60 Hz, with exposure times of 12, 6, and 4 minutes respectively, peak-to-peak amplitude of 4 mm, with knees in 60 ${}^{\circ}$ flexion. After 12 weeks of intervention, a significant improvement was observed for isokinetic muscular strength of knee extensors at 60 ${}^{\circ}$ /s and 180 ${}^{\circ}$ /s, but only for the group that performed WBV at 40 Hz.

However, studies that have administered WBV associated with lower limb muscle strengthening exercises (such as squats during WBV) have identified significant improvement in lower limb muscle strength in postmenopausal women, when compared to relaxation exercises [24] or no treatment [25]. Von Stengel et al. [24] using synchronous vibration (35 Hz, peak to peak amplitude of 1.7 mm) and side-alternating vibration (12.5 Hz, peak to peak amplitude of 12 mm), with an exposure time of 15 minutes, found that, after 12 weeks of intervention, both types of vibration allows a significant improvement in isometric muscular strength of the knee extensors at 100 ${}^{\circ}$ /s. Verschueren et al. [25] when using synchronous vibration between 35 and 40 Hz, peak to peak amplitude of 1.7 to 2.5 mm, for 30 minutes, identified a significant improvement in isometric and isotonic muscular strength of the knee extensors after six months of intervention. In these studies the relative effects of strengthening exercises and WBV cannot be partitioned, considering that the authors did not use a third group with WBV alone.

A meta-analysis concluded that WBV compared to no intervention provides significant effects on dynamic knee extension strength and isometric leg extension strength in older adults but no differences when compared to other physical exercise modalities. In addition, WBV did not increase isometric knee extension strength when compared to no intervention or other forms of exercise [22]. However, the authors did not perform subgroup analyzes considering in isolation studies that performed muscular strengthening exercises during WBV, or for different frequencies, magnitudes, types of vibration, or time of exposure. Meta-analysis studies should strive to perform subgroup analyzes in which studies with different interventionsare considered separately, thus making it possible to identify the source of effects identified in the analysis.

The performance of dynamic exercises during WBV is likely to be an important moderating variable for gaining muscular strength. Another meta-analysis study involving different populations concluded that in WBV interventions in which participants perform dynamic and isometric muscle contractions, muscular strength gain is almost double compared to interventions using isometric contraction alone (such as remaining in a semi-flexed knee position) [48]. It was also concluded that synchronous platforms were more effective for gaining muscular strength when compared to side-alternating type platforms [48], which may explain the lack of significant results for WBV in the present study.

In the current study, when comparing WBV and Pilates, a significant difference ( $p<$ 0.05) was observed only for the peak isokinetic torque of the knee flexors at 60 ${}^{\circ}$ /s, where Pilates was superior, with a moderate effect size ( $d=$ 0.70). For the knee flexors at 180 ${}^{\circ}$ /s, there was no significant difference ( $p>$ 0.05). To our knowledge, to date, no study has compared the effects of WBV with any other form of physical exercise on the peak isokinetic torque of the knee flexors, which necessitates further investigation.

The present study did not find significant differences between WBV and Pilates for the peak isokinetic torque of the knee extensors at 60 ${}^{\circ}$ s and 180 ${}^{\circ}$ /s. Other randomized trials comparing WBV with different forms of physical exercise also did not identify significant differences for isokinetic muscular strength of knee extensors in postmenopausal women [25, 32, 35]. In addition, a meta-analysis that compared the effects of WBV with different forms of physical exercise did not find significant differences between techniques for dynamic force of knee extension, isometric leg extension force, vertical jump, or sit-to-stand test [22].

Interventions involving WBV use low exposure time, while in the different forms of physical exercise the interventions have significantly longer duration. Thus, the differences between WBV and Pilates for the peak isokinetic torque of knee extensors presented in the present study may have occurred as a result of the difference in exposure time of five and 60 minutes respectively.

4.3 Quality of life

Regarding quality of life, the PG was superior to the CG for four domains (role-physical, bodily pain, social functioning and role-emotional) of the SF-36 questionnaire. Pilates exercise appeared efficient for improving quality of life in components related to physical health and mental health. Other studies that used the same questionnaire in postmenopausal women found, after 12 weeks of Pilates,significant effects on the quality of life in favor of Pilates when compared to stretching exercises [15] and exercises performed at home, without professional supervision [16]. Campos de Oliveira et al. [15] observed improvement for six domains of the questionnaire, while Küçükçakır et al. [16] reported improvement for all eight domains.

Studies that used other questionnaire models to assess quality of life also identified significant improvements after Pilates compared to no treatment controls [7, 17]. Angın et al. [7] found improvement for all domains of the QUALEFFO-41 questionnaire in postmenopausal women after six months of Pilates. Siqueira Rodrigues et al. [17] after 8 weeks of intervention with the method, reported an improvement in the overall quality of life index, measured by the WHOQOL-OLD questionnaire, in older women. In addition, a meta-analysis, summarizing the results of different studies of Pilates on the quality of life in older adults, concluded that the technique was associated with a large effect size ( $d=$ 0.94) for this variable [18]. The meta-analysis, however, assessed an aggregate measure of activities of daily living, mood states and quality of life.

No significant differences between VG and CG were found in SF-36 scores. Few studies to date have observed the effects of WBV on quality of life in older adults. Bruyere et al. [27] compared two groups that participated in conventional physiotherapy and one of these groups complemented the intervention with WBV and found imporvements in all SF-36 domains for the WBV group. On the other hand, Santin-Medeiros et al. [30] after 8 months of WBV, did not observe differences for any SF-36 domain compared to no treatment controls.

In the present study, there were no significant differences in the comparisons between WBV and Pilates for the domains of quality of life measured by the SF-36. Given that few studies to date have observed the effects of WBV on the quality of life of postmenopausal women, and that no study has compared the technique with another form of physical exercise, further validation studies should be performed. The Pilates sessions lasted approximately 60 minutes, while the WBV sessions lasted only five minutes. Consequently, Pilates allowed greater social interaction among participants, which may explain the results of the present study for quality of life only of the Pilates group compared to the control group, but not for vibration compared to control.

4.4 Strengths and limitations

This was the first study to identify the effects of Pilates compared to WBV on muscular strength and quality of life in postmenopausal women. To our knowledge, this was also the first study to investigate the effects of WBV on the peak isokinetic torque of the knee flexors in postmenopausal women. Another strong point is the adherence of the participants to the intervention, with loss of only two volunteers from the control group, as well as the attendance frequency rate in the two intervention groups that was higher than 90%. As limitation, since the study included an intervention involving physical exercise, it was not possible to mask the participants and the professionals who ministered the interventions.

5. Conclusion

Six months of Pilates three times per week was superior to WBV for the peak isokinetic torque of knee flexors in postmenopausal women, while no difference between techniques was observed for the peak isokinetic torque of knee extensors or quality of life. Pilates was superior to no intervention in the variables of peak isokinetic torque of knee extensors and flexors, and for four of the eight domains of the SF-36 questionnaire. WBV was not significantly different to no intervention for these same variables.

Footnotes

Conflict of interest

There is no conflict of interest.

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Effects of the Pilates exercise compared to whole body vibration and no treatment controls on muscular strength and quality of life in postmenopausal women: A randomized controlled trial

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Method

2.1 Recruitment and participants

2.2 Evaluation of muscular strength

2.3 Evaluation of quality of life

Table 1 Pilates exercise – Protocol 1 and 2

2.5 Intervention

2.5.1 Pilates group

2.5.3 Control group

Table 2 Baseline characteristics of participants

Table 3 Between group comparisons for isokinetic muscular strength (in Nm) between baseline and follow-up

3. Results

3.1 Participation

3.2 Baseline characteristics

3.3 Muscular strength

Table 6 Comparisons of pairs for quality of life (SF-36 score)

3.5 Adverse events

Table 7 Summary of adverse events

4.1 Summary of the main results

4.2 Muscular strength

4.3 Quality of life

4.4 Strengths and limitations

5. Conclusion

Footnotes

Conflict of interest

References

Table 1
Pilates exercise – Protocol 1 and 2

Table 2
Baseline characteristics of participants

Table 3
Between group comparisons for isokinetic muscular strength (in Nm) between baseline and follow-up

Table 6
Comparisons of pairs for quality of life (SF-36 score)

Table 7
Summary of adverse events