1. Introduction
When body composition analysis reveals abnormalities such as excess body fat or skeletal muscle deficiency, the recommended therapeutic approach is to modify the diet and to introduce physical activity. Movement such as exercise is a well-known method of prevention and therapy for modern diseases. It improves endurance and increases skeletal muscle mass, reduces fat mass and the activity of the cardiovascular system, and prevents the development of osteoporosis by increasing bone mineral density. However, there is a group of people who have difficulty performing any physical exercise. It is associated with age, the presence of diseases of the musculoskeletal system, or simply a lack of motivation or an unhealthy lifestyle [
1,
2]. One method that can reinforce or support physical activity is whole-body vibration (WBV).
Whole body vibration (WBV) therapies have become popular. Many types of WBV devices are used, which differ in vibration parameters, such as frequency, amplitude, direction, and type of signal. The amplitude range of the platforms generating sinusoidal vertical (rhythmic) vibrations is 0–12 mm, and the frequency range is 30–60 Hz. The amplitude range of the side-alternating sinusoidal (rhythmic) vibrations is 0–12 mm, and the frequency range is 5–30 Hz. The amplitude range generating stochastic (arrhythmic) vibrations is 0–2 mm, and the frequency range is 1–12 Hz [
3,
4].
The use of WBV influences processes in the human body at various levels, starting from the activation of receptors and muscle response, through changes in hormone concentrations and the release of neurotransmitters, to the activation of many areas of the brain [
4,
5]. In their latest studies, Dos Santos et al. [
6] showed an increase in irisin levels, a decrease in levels of redox status markers, and reduced visceral adipose tissue mass after six weeks of WBV procedures. Vibration devices with stochastic resonance generate vibrations of varying amplitude and frequency. The patient stands with each foot on a separate platform, and the platforms vibrate independently. The body is constantly thrown out of balance. The vibration frequency is randomized; it constantly changes within certain limits, and the movements are impossible to predict. The neuromuscular system must react effectively to changes in a short time. This is particularly important among the elderly or among patients with movement disorders, when long-lasting and intense training sessions are not recommended [
5,
7,
8].
A number of scientific reports show a positive effect of physical activity on body composition [
2]. In the literature, we can also find evidence of the positive impact of vibrations with stochastic resonance on other aspects of the human body, e.g., balance, muscle pain, and cognitive functions [
9,
10,
11]. The impact of stochastic resonance whole body vibrations on individual parameters of female body composition have never been studied before. To assess the suitability of SR-WBV devices for fat mass reduction, a particular group of body composition parameters were selected: fat mass, percent body fat, and visceral fat area were analyzed. Due to the activation of muscle spindles and osteogenic response after stochastic resonance, as reported in the literature [
12,
13], the fat-free body components measured by the In Body S10 device, including the most important parameters such as muscle mass, cellular mass, proteins, and bone minerals, were tested. As additional parameters, the water components were also measured.
Young, healthy women with normal body composition were recruited for the experiment. This research was treated as a preliminary study to first examine the usefulness and additionally prove the safety of the SR-WBV procedure in young, healthy women before it can be implemented in older women, women with abnormal body composition, or women with various diseases.
2. Materials and Methods
2.1. Study Design
This study was designed as a preliminary controlled before–after (CBA) study, where two groups were compared with each other; in one group a SR-WBV procedure was carried out and in the other group no intervention was conducted (the control group). We hypothesized that the whole-body vibration procedure with stochastic resonance influences body composition in healthy young women, especially on parameters such as fat-free mass, skeletal muscle mass, and visceral fat area. Two groups were selected from among all participants of the study: Group V—women who received SR-WBV vibrations and Group C—women who did not receive SR-WBV. Assignment to C and V groups was randomized. In the control C group the volunteers had a BC measurement before and then after 6 weeks, no intervention was performed between the BC measurements. The participants were informed not to change their current lifestyle, i.e., a change in diet or physical activity in the period of time between BC measurements. Two groups were compared with each other; in the V group a SR-WBV procedure (12 sessions over 6 weeks, two times a week, with a minimum of 1 day break) was carried out, and in C group no intervention was conducted (control group), in order to fully illustrate the influence of SR-WBV on the parameters of body composition. Body composition was measured in all participants twice at the beginning of the experiment and again six weeks after the first measurement. The BIA parameters were compared before and after the procedure in V group and compared with the results in group C.
The study was conducted in accordance with the Helsinki Declaration. Every participant provided written consent after being informed about the aim, the protocol, and the methods of the study. The research project was approved by the Bioethics Committee of the Medical University of Silesia (KNW/0022/KB1/49/13).
2.2. Body Composition Analysis
Body composition was measured in all participants at the beginning of the experiment. The bioelectric impedance analysis (BIA) was performed using an InBodyS10 (BioSpace; Seoul, Republic of Korea) device. The electricity parameters during the bioimpedance measurement were as follows: Impedance Z (Ω): 1 kHz, 5 kHz, 50 kHz, 250 kHz, 500 kHz, and 1 MHz; Reactance X (Ω): 5 kHz, 50 kHz, and 250 kHz; Whole Body Phase Angle Ø (°): 50 kHz. BIA measures the electrical properties of body tissues and allows us to estimating body composition parameters. The BIA assessment of body composition was based on the volume of body fluids and the BIA resistance value. Bioelectrical impedance is defined as the opposition of a conductor to the flow of alternating electric current applied to it. The bioimpedance varies depending on the composition of the tissue as well as the frequency of the applied current. BIA can be performed by applying electric current of different frequencies simultaneously. At low frequencies (1–5 kHz), the electric current does not penetrate the cell membrane, so it is assumed to flow through the extracellular fluid. Conversely, at higher frequencies (>50 kHz), the current flows across cell membranes and is associated with both intracellular and extracellular fluid compartments.
Before starting the body composition measurement, the height and body mass of the participants were measured. The height and weight of the participants were measured using a Momert 5967 electronic column scales with a height rod (Hungary), with an accuracy of d = 100 g and maximum capacity = 200 kg. The subjects had not consumed a meal for at least 4 h prior to the examination. Immediately before the measurement, participants were asked to empty their bladder and then remained supine for 15 min. After this time, electrodes were placed to the thumb and middle finger of the right and left hands and the ankles of the right and left lower limbs, and body composition was measured.
Measured BIA parameters included fat mass (FM, kg), percent body fat (PBF, %), visceral fat area (VFA, cm2), soft lean mass (SLM, kg), fat-free mass (FFM, kg), skeletal muscle mass (SMM, kg), body cell mass (BCM, kg), protein (kg), minerals (kg), bone mineral contents (BMC, kg), intracellular water (IW, l), extracellular water (EW, l), total body water (TBW, l), extracellular water/total body water (EW/TBW). Six weeks after the first measurement, all participants underwent the body composition analysis again.
2.3. SR-WBV Procedure
The Zeptor med® plus Noise (Frey AG, Zurich, Switzerland) device was used for the vibration procedure. The platform consisted of two plates emitting vibrations of different directions and variable force. The movement of both plates was heterogeneous and occurred in all directions, i.e., up/down, forward/backward, right/left.
During the vibration, the examined person took a standing position, straightened with the lower limbs slightly bent at the knees. Each foot, without shoes, was placed on a separate plate of the device (
Figure 1). After starting the procedure program, the plates began to move, gradually increasing in frequency and amplitude until the desired intensity was achieved. The trainee remained relaxed, and the torso and head were kept as still as possible. One procedure session lasted 15 min, consisted of 9 active series of vibrations lasting 45 s each with 40 s breaks between series during which the plates did not move. The whole stochastic cycle consisted of 12 sessions over 6 weeks, two sessions a week, with a minimum of 1 day break between sessions. The vibration frequency ranged from 2 to 8 Hz, and the amplitude ranged from 0.5 to 3.5 mm.
2.4. Statistical Analysis
The statistical analysis was performed using the Statistica 13 software (Statsoft Polska, Kraków, Poland). To assess the normality of distribution, histograms were drawn and the Shapiro Wilk test was performed. To assess the homogeneity of variance, the Leven test was performed. The data were normally distributed, and the variances were homogeneous. No statistically significant differences in the selection of the control group between groups C and V regarding age, height, or body mass were confirmed using an independent samples Student’s t-test. The ANOVA test (Analysis of variance for repeated measurements, parameterization with sigma-constraints, decomposition of effective hypotheses) was used to analyze the impact of vibration in the V group and the effect of time in the C group, and to evaluate the differences between the V and C groups. Significance was set at p < 0.05.
4. Discussion
There are no studies in the available literature that describe the effect of SR-WBV on the parameters of human body composition. Only studies examining the effect of WBV on human body composition have been performed. However, those studies were characterized by different vibration parameters and procedure conditions. In 2008, a study performed on rats suggested that long-term WBV exposure reduced adipogenesis [
15]. The female healthy rats were assigned by body mass into one of three groups (8–10 per group): baseline, vibration, or control. The baseline group was sacrificed at initiation of the study for analysis of body composition, bone mass, and muscle function. For vibration treatment, animals in the vibration group were placed in vibration platform. This group received 30 min of whole-body vibration each day, 5 days per week, for 12 weeks. The non-vibration animals remained in their cages. Studies resulted in significant body composition differences between the vibration and control groups. The whole-body vibration group weighed less, had less body fat, and had a lower overall PBF than the age-matched non-vibration group. In addition, the vibrated rats had lower serum leptin levels than the control animals. However, differences in food intake were not observed between the two groups [
15]. Milanese et al. [
16] conducted a study involving 36 healthy, non-obese young women. They performed the whole-body vibration procedure over 8 weeks, twice a week. WBVT caused a reduction in women’s total body FM and an increase in women’s SLM. As in this study, women’s body mass and BMI values did not change significantly. In a study performed by Demirel et al. [
17], a six-week gymnastic exercise combined with whole-body vibration (WBV 25–50Hz) resulted in greater improvements in human body composition than exercise alone. There was no improvement in the untrained control group of participants. De Silva et al. [
18] measured and compared energy expenditure in men when performing half squats with and without WBV. It was found that an 11.5minute series of exercises among participants (five sets of 10 repetitions with a 2-minute recovery interval between sets), along with vertical sinusoidal vibrations of 30 Hz frequency and 4 mm amplitude, increased energy expenditure during both exercise and recovery, compared to the same series of exercises with no vibrations among participants. Heart rate did not differ significantly between groups of participants. The authors summarized the results as showing that it would be feasible to introduce vibration exercises into regular training programs, particularly those whose key objective is muscle hypertrophy along with fat reduction [
18]. These were sinusoidal vibrations; in our study a greater impact on the women’s metabolism of stochastic vibrations was assumed, through a higher threshold of neuromuscular excitability, as in the study by Elfering et al. [
19], where it was proved that human muscular activity and energy expenditure rose during verum SR-WBV compared to baseline and sham SR-WBV.
Most recent studies have focused on assessing the effects of WBVT on human body composition in overweight or obese people. Omidvar et al. [
20] found small effects of WBV on total FM per kg among the adult general population of people who had normal BMI. The general results of the systematic review and meta-analysis by Alavinia et al. [
21] showed a positive effect of WBV on FM among healthy adults who are overweight or obese at baseline, especially when added to other conventional weight loss interventions such as diet and exercise. Sanudo et al. [
22] reported a significant decrease in the PBF after 8 weeks of exercise with WBV among obese people, while no changes were observed in both the Exercise and Control groups of participants. Severino et al. [
23] studied Hispanic postmenopausal obese women and showed that 6 weeks of WBV decreased the women’s PBF compared to both the baseline and control groups. Also noteworthy is a study from 2023 [
6] that assessed the impact of WBV on the human level of irisin, as well as the level of oxidative stress markers and body composition among participants. It was found that the WBV procedure three times a week for 6 weeks was sufficient to produce results at the human metabolic level, as demonstrated by the increase in irisin among participants, which is an anti-obesity and anti-diabetes factor, and the reduction in oxidative stress markers and visceral adipose tissue, which are more metabolically active and more insulin-resistant. In contrast to the previous study, Alvarez et al. [
24] applied low-to-high amplitude vibration for 6 weeks in a trial among 38 overweight and obese women and showed no statistically significant differences in women’s PBF among the WBV and control groups. However, when analyzing the latest literature, in the next phase of the research project the impact of SR-WBV should be investigated primarily on overweight and obese people.
There are no data available in the literature on the effect of SR-WBV on human body composition. Scientific publications on the impact of SR-WBV on the human body mainly concern the aspect of human fitness, muscle strength, and balance among the elderly [
6,
25]. Rogan et al. [
25] reported that the SR-WBV procedure had a positive effect on muscle strength and fitness in the elderly. Herren also observed an increase in participant’s muscle strength after the SR-WBV procedure [
26]. As there is scientific evidence of side effects of the stochastic resonance whole-body vibration procedure [
27], in this paper, we decided to test young and healthy individuals first, minimizing the risk of potential side effects. We also assumed that the use of stochastic WBV, which showed higher human muscle activation than sinusoidal WBV [
28] would be sufficient. However, it was found that the parameters of SR-WBV vibrations were too weak to significantly affect the body composition of young and healthy women.
Limitations
During the research program, the methodology of the study protocol revealed some imperfections. While designing the experiment, the research of other authors available in the literature was followed. The randomized way of classifying participants to the study groups seems less sensitive to the impact of vibrations. The groups differed from each other in terms of the women’s body composition. Once again, the poor usefulness of the BMI index in the classification of human body mass [
29] has been proven. More elaborate group selection criteria should be used in future experiments.
In order to fully illustrate the influence of SR-WBV on the parameters of human body composition, the study group should be supplemented with men, people with abnormal body composition, and older people.
In future experiments that use the stochastic resonance whole-body vibration platform in healthy volunteers, one should consider changing the procedure program: vibration parameters, duration, and frequency of vibrations. The SR-WBV procedure program, with the weak parameters used in this study, is not sufficient as a training stimulus in young healthy women.