The immediate effect of a single whole-body vibration session on balance, skin sensation, and pain in patients with type 2 diabetic neuropathy

Abstract

Purpose

Patients with diabetic neuropathy usually suffer from impaired balance, pain, and decreased sole-foot sensation. The present research was designed to appraise the relic of whole-body vibration (WBV) on balance, pain, and sole-foot sensation in diabetic neuropathy patients.

Methods

Present study was a single-blind randomized controlled clinical trial. Thirty-four patients with type 2 diabetic neuropathy were randomly divided into intervention groups (n=17) and control (n=17). The therapeutic program in the intervention group included standing on the platform of the WBV device, and in the control group included using the device in off mode. Dynamic balance (including overall, anterior-posterior, and medial-lateral stability indices) was measured using Biodex device, functional balance with timed up and go (TUG) test, pain using the visual analog scale (VAS), and sole-foot sensation of both feet with a monofilament. The outcomes were measured in both groups before and after the interventions.

Results

Sixteen people in each group were analyzed. Intra-group comparison showed a significant improvement in the mean pain (P = 0.000), functional balance (P = 0.011), right and left sole-foot sensation (P = 0.001), and overall (P = 0.000), anterior-posterior (P = 0.000) and medial-lateral (P = 0.000) stability indices for the intervention group in post-intervention compared to pre-intervention. However, changes in the control group were not statistically significant. Results of inter-group comparison indicated a significant improvement in all parameters in the intervention group, except for functional balance.

Conclusion

WBV can be effective in reducing pain and improving the sole-foot sensation and dynamic balance.

Introduction

Diabetes is a long-lasting health condition in which glucose metabolism, insulin output, or both are disrupted [1]. Damage to peripheral nerves located outside of the brain and spinal cord is called peripheral neuropathy, which is one of the long-term adverse effects of diabetes in the form of microvascular complications [2]. Motor neuropathy causes the loss of the nerves nourishing muscles, leading to various abnormalities from muscle weakness to severe deformities. Walking is also impaired in more advanced stages due to the sensory disturbance and subsequent change in balance indices, and the person is prone to falling [3].

Decreased proprioception in the foot and ankle is a significant cause of imbalance [4]. Diabetic neuropathy patients are 15 times more likely than healthy individuals to fall [5]. Falling may result in more severe physical and psychological accidents in the elderly with diabetic neuropathy [6]. Tissue repair sometimes requires long-term periods of immobility, thereby reducing patients’ independence and quality of life [7]. Pain is also one of the main complaints of these individuals, which severely affects their quality of life [8]. If complications of the patients with diabetic neuropathy are not managed, the symptoms will progress and lead to reduced quality of life. Therefore, addressing this issue and finding appropriate treatment for these patients is vital in clinical practice.

Various treatments have been suggested to inhibit the progression of neuropathy. Medication therapy is the first step in managing the progression of the symptoms [9]. Since this therapy is effective in only 30% of cases associated with side effects, researchers are looking for non-medication therapies such as physiotherapy [9]. Among physiotherapy techniques, reports have shown the benefits of exercise therapy to improve balance and reduce pain [10]. However, because older neuropathic patients have experienced falling at least once, they often experience fear of re-walking along with decreased self-confidence and gait speed. Therefore, these patients usually do not have proper compliance and cooperation in exercise therapy because learning and performing the exercise in older patients with diabetic neuropathy is reduced. Whole-body vibration (WBV) is one of the physiotherapy techniques, and there have been many kinds of research on its effect on people with various conditions, including cardiovascular disease [11], chronic obstructive pulmonary disease [12], and osteoarthritis [13]. However, to our information, few studies have focused on balancing indices and skin sensation. Possible efficiency of WBV can include improvement in joint proprioception [14], muscle reflex, motor units [15], pain control gates [16], stimulation of tonic vibration reflex [16], sensory inputs [8], and tissue and skin circulation [17]. Due to insufficient blood supply to the nerves in these patients, nerve repair can be expected through the mechanism of action of WBV on increasing blood flow and oxygen supply [14, 15]. Considering the effects of WBV, the present study aimed to investigate the effect of a single WBV session on balance, pain, and skin sensation of foot in patients with type 2 diabetic neuropathy.

Methods

Patients

This single-blind randomized trial was carried out in a hospital affiliated with Shahid Beheshti University of Medical Sciences. A total of 34 female patients with type 2 diabetic neuropathy were randomly assigned to intervention (n = 17) and control (n = 17) groups. All patients were evaluated for laboratory tests, fasting blood sugar levels, and HbA1c to determine if diabetes was under control and homogenize participants in the two groups. Clinical evaluation forms, including duration of disease, the severity of symptoms, and a Michigan questionnaire, were used to determine the severity of neuropathy filled out by a physiotherapist. Inclusion criteria were 40–75 years old patients with type 2 diabetes [18], body mass index between 25 and 35 [19], diabetes control with oral medications (no-insulin injection) [20], Michigan test score 13–29 (moderate diabetic neuropathy) [21], HbA1C <8.5%, and controlled blood sugar in the last three months [22]. Exclusion criteria also were diabetic infectious wounds, neurological diseases (other than diabetic neuropathy) and rheumatoid, vestibular system disorders, vision disturbances, sole foot and toe ulcers [23], history of trauma, injury and surgery in the lumbar region, using knee or pelvic prostheses [21], history of epilepsy, and cognitive problems [21].

After readership and signing a written informed consent form, patients were included in the study. The current study was confirmed by the Ethics Committee of Shahid Beheshti University of Medical Sciences (IR.SBMU.RETECH.REC.1396) and registered at the Clinical Trial Center of Iran (IRCT20180302038912N1).

Tools

Dynamic balance, functional balance, pain, and sole-foot sensation were measured using the Biodex balance system, timed up and go test (TUG), visual analog scale (VAS), and monofilament instrument, respectively.

Dynamic balance

The US-made Biodex Balance Scale, having a movable platform with a tilt angle of 20° in each direction, was utilized to measure the dynamic balance. This device shows medial-lateral stability index, anterior-posterior stability index, and overall stability index. This stabilometry consists of 8 levels, and the difficulty level increases from level one to eight, respectively [24]. The initial evaluation repeated the equilibrium tests five times due to reduced learning effects [24]. The result of the last test was recorded as the final result. The patient stood on a moveable platform with the width of the selected base of support. The coordinates of the foot’s sole points on the moveable platform were recorded to maintain the same conditions in all tests. The stability Level of the moveable platform was selected at relatively rigid (level 6) [24]. While the platform was released for slipping under the patients’ feet soles, they were asked to hold their center of pressure on the middle of the monitor screen for one minute. Participants fully stretched their arms at the side of the body or crossed their arms over their chests. There was a one-minute interval between each test. After the fifth test, the device showed the level of anterior-posterior and medial-lateral deviations in each test. Then was determined overall, anterior-posterior, and medial-lateral stability indices.

Timed up & go test (TUG)

This test evaluates functional balance. During this test, the examiner measured how long it took a person to get up from the chair, walk three meters, turn around, and sit on the chair [25].

Sole-foot sensation

Monofilament is a technique to diagnose diabetic neuropathy. This test is usually applied to sole-foot skin. When a person has a loss of sole-foot sensation, he/she cannot recognize this pressure. This test has the Cronbach’s alpha coefficient of 0.72 and reliability of 0.89 approved in a previous study [26]. In this study, the patient sat and closed her eyes. Then the examiner pressed the 10-g monofilament for 10 min on each point of the two feet. Ten points on each sole, including 3 points on the first, second and third toes, 3 points on the first, second, and third metatarsal heads, 3 points on medial and lateral sides of midfoot, one point on heel region, and one the dorsum of foot, were selected and each filament was placed on each of these 10 points. The patient was asked to report whether the filament hit her sole foot and where it hit. Each of these points had one score if the patient felt the applied pressure. It should be noted that inability to perceive the monofilament at any site was considered abnormal. The total score of each foot is 10 [27].

Evaluation of pain intensity

Pain intensity was assessed using the VAS questionnaire. This scale includes a 100 mm straight ruler. The patient marked her sensation about pain intensity and discomfort as a dot on the streak [28]. The pain intensity in the lower extremities was recorded from 0 mm (lowest pain to 100 mm (highest pain).

Procedure

First, study outcomes were evaluated before the interventions in both groups. Then, the people in the intervention group stood on the WBV platform, holding their arms stretched at the side of the body or crossing their arms over their chests. Patients were trained to keep their knees bent up to 30°, and angular retention was assessed using a pointer laser so that if knees got more bent or straight, the light passing through the front and back of the knees would intersect the dark platforms next to the device [29]. The safety switch was attached to the patient’s clothing, which stopped the vibration in the case of imbalance. The load on a body with a protection limit can be calculated using a formula. The acceleration experienced by the body is estimated using the following formula:

a = A*(2π f)².

Where “a” is the acceleration experienced by an individual, which is the same as the acceleration of gravity; “A” refers to the displacement value whose standard value is between 1 and 11 mm, f denotes vibration frequency in terms of Hz whose average value is between 15 and 60 Hz. People usually experience an acceleration between 2.2 to 5.1 g in most studies. In this study, the device vibrated its bottom platform at a frequency of 30 HZ and an amplitude of 2 mm during 30 s, which are safe values [30]. This step was repeated six times, and there was a one-min interval between each step. In the control group, patients stood on the device platform, and the same sound was played for them for 30 s. This sound was played to approximate the effects of the placebo in the intervention and control groups (estimated time: 10 min). The patient in the control group thought that the device induced a vibration that could not be felt.

The pain, sole-foot sensation, dynamic balance test, and functional balance test were immediately measured after using the WBV device in both intervention and control groups.

Statistical analysis

Shapiro-Wilk test was used to check the normality of the data. Regarding the intra-group analysis, a paired t-test of pre-post intervention in each group was used for normal distribution of data, and a Wilcoxon test for non-normal distribution. Concerning the inter-group analysis in pre-and post-intervention, an independent t-test was used for normal distribution of data and a Mann-Whitney test for non-normal distribution. The mean ± standard deviation and p values for the parameters measured were presented for descriptive statistics. The data were analyzed using SPSS 22 software, and P value ​​less than 0.05 was considered a significant level.

Results

During the study, two patients were excluded: one from the intervention group due to system phobia and the other from the control group due to a notable rise in blood pressure. Therefore, 32 female patients, with a mean age of 60±7.22 years in the intervention group (n=16) and 50±7.6 years in the control group (n=16), completed the study and were analyzed. Table 1 shows the mean age, weight, height, BMI, diabetes history, trimester sugar, and fasting blood sugar levels in both categories. The normality results demonstrated a normal distribution for the data related to pain, dynamic balance, and functional balance, but non-parametric tests were utilized for right and left sole-foot sensation due to their non-normal distribution.

Table.1.

Comparison of demographic characteristics in the two groups

Parameters (unit)	Intervention group Mean ± SD	Control group Mean ± SD	P value
Age (year)	60±7.22	50±7.62	0.705
Weight (kg)	74.93±4.96	72.54±7.63	0.302
Height (cm)	157.78±3.18	158.84±3.99	0.412
Body mass index (kg/m2)	30.17±2.15	28.69±2.77	0.102
History of diabetes (year)	6.37±4.95	5.87±2.75	0.726
HbA1c (mg/dl)	6.88±0.24	6.78±0.39	0.427
Fasting blood sugar level (mg/dl)	165.56±42.22	167.25±32.07	0.899

The variables listed in Table 1 were not significantly different between the two groups

Intragroup comparison

The results demonstrated a significant reduction (improvement) in the mean pain score (P = 0.000), functional balance (P = 0.011), overall stability index (P = 0.000), anterior-posterior stability index (P = 0.000) and medial-lateral stability index (P = 0.003) in the intervention group after a single WBV session compared with pre-intervention (Tables 2 and 3). Moreover, after the intervention, in the intervention group, the sensation of both feet soles (P = 0.001) significantly increased. (Table 2). However, there was no significant variation in any variables of the control group between the pretest and posttest phases (Tables 2 and 3).

Table.2.

Mean, standard deviation, and level of significance in scores of pain and right and left sole-foot sensation

	Intervention group			Control group
Variables	Pre-intervention	Post-intervention	P value (Intragroup comparison)	Pre-intervention	Post-intervention	P value (Intragroup comparison)	P value (Intragroup comparison after intervention)
Pain (Based on VAS)	3.97±0.65	2.34±0.54	0.000**	3.72±0.74	3.39±0.67	0.105	0.000**
Right sole-foot sensation	6.93±0.558	9.43±0.181	0.001**	7.68±0.643	7.25±0.673	0.180	0.000**
Left sole-foot sensation	7.25±0.512	9.31±0.253	0.001**	7.43±0.569	7.37±0.597	0.679	0.000**

a: non-parametric data, **p≤ 0.001

Table.3.

Mean, standard deviation, and significance level in functional balance, overall, anterior-posterior, and medial-lateral stability indices

		Intervention group			Control group
Variables		Pre-intervention	Post-intervention	P value (Intragroup comparison)	Pre-intervention	Post-intervention	P value (Intragroup comparison)	P value (Intragroup comparison after intervention)
Functional balance		11.70±0.649	11.08±0.654	0.011*	0.577±11.27	10.92±0.570	0.131	0.389
Dynamic balance	Overall SI	0.24±2.95	1.77±0.12	0.000**	0.09±1.98	0.10±2.08	0.060	0.000**
	Medial-lateral SI	0.181±2.49	1.44±0.125	0.000**	0.102±1.55	0.086±1.67	0.336	0.000**
	Anterior-posterior SI	0.223±1.76	1.23±0.120	0.033*	0.104±1.40	0.067±1.41	0.798	0.027*

SI: stability index, *p˂0.05, **p˂ 0.001

Intergroup comparison

Intergroup comparison of post-treatment results showed a significant improvement in all parameters, except functional balance, in the intervention group (Tables 2 and 3).

Discussion

WBV can have an immediate impact in relieving the suffering of patients with type 2 diabetic neuropathy, according to the findings of the present research, which are compatible with those of Caputo et al. [31]. It can likely be said that a single WBV session led to a decrease in the pain intensity by inhibiting the senses in the peripheral nervous system, according to the theory of pain gate control [31]. On the other hand, the acute influence of vibration on pain relief could be explained by mechanisms in the nervous systems. WBV-induced pain relief may be related to the inhibition resulting from the connection of Aβ-type sensory fibers and stimulation of specific mechanoreceptors such as Pacini corpuscles [32]. This phenomenon reduces the painful inputs of C fibers by activating the inhibitory circuits of the posterior horn of the spinal cord [19]. Some researchers have referred to increased blood flow and skin temperature as the immediate effects of using WBV [32], which may explain the reduction in pain intensity and increase in sole-foot sensation among patients with diabetic neuropathy for the findings of this study.

On the other hand, WBV (30 HZ, 2 mm) could immediately affect dynamic balance, including the overall, anterior-posterior, and medial-lateral stability indices, among female patients with type 2 diabetic neuropathy. In the present study, the knee flexion angle was considered 30 degrees to minimize lateral vibration transmission to the head [30]. These effects are in line with the reports of studies by Alves et al. [33], Torvinen et al. [34], and Murakami et al. [35], performed on healthy young people [34]. Single WBV sessions improved dynamic balance indices, probably due to increased firing of motor units, increased muscular and joint stiffness, improved coordination patterns between synergistic and antagonistic muscles, neural adaptation, and improved proprioception [34, 36]. Inconsistent with the present study, Mahbub et al. found no improvement in balance indices in elderly and healthy individuals [29], which may be due to the vibration level used in the current study, which was not as high as in other studies. Another reason may be that older participants of the present study were healthy and physically active with a good level of balance and mobility.

The present study results indicated that the use of WBV had no immediate effect on improving TUG in diabetic patients. This finding was consistent with Del Pozo-Cruz’s results on patients with diabetic neuropathy [10]. A possible reason for no difference in functional balance may be that patients of the present study were told to walk safely rather than at their self-selective speed. Consistent with the present study, Eduardo et al. carried out a study on patients with multiple sclerosis [37]. Patients with multiple sclerosis and diabetic neuropathy both suffer from weakness of the neuromuscular system, which may explain the immediate ineffectiveness of WBV on TUG. However, inconsistent with the present study, Yoosefinejad et al. and Torvinen et al. believed that using a single WBV session increased the firing rate of motor units, thereby improving muscular strength and control in patients with multiple sclerosis. The researcher used only limited clinical tests on that study, which resulted in little fatigue for patients. So their method may be a reason for the different results of their study from the present study. Also, WBV efficiency on functional balance may require more sessions to be addressed in future investigations [21, 36].

The results also demonstrated that WBV could immediately improve the right and left sole-foot sensation in individuals with diabetic neuropathy. It seems that inactive vibration and touch induced by the WBV device can improve balance by activating the foot sole nervous system [38]. In a study on stroke patients, Naghdi et al. observed the same significant improvement [39]. One possible reason for the WBV-related improvement in sole-foot sensation could be activating skin receptors by stimulating the afferents and efferents. However, the studies by Pollock et al. [40] and Schlee et al. [41] were not consistent with the present results. However, those two studies were performed on young and healthy individuals. Also, the discrepancy in the results could be due to the adequacy of skin blood supply in healthy people compared to people with neuropathy.

There were some limitations to the present study. Only one session of WBV was taken. Therefore, it is suggested to determine this effect within more sessions in future research. Also, due to the executive limitations, the present study was performed only on female patients. Therefore, it is not feasible to weigh the effects of the intervention on both sexes. So it is suggested that both sexes be taken in future studies. Finally, a follow-up period should be considered to control any symptoms during treatment and compare the results with other exercise interventions in patients with type 2 diabetic neuropathy.

Conclusion

The present study results showed that WBV could immediately reduce pain, improving sole-foot sensation and dynamic balance, but not functional balance.