Effects of Adding Whole‐Body Vibration to Routine Exercise Therapy on Pain, Disability, Muscle Strength, and Endurance in Individuals With Chronic Nonspecific Neck Pain: A Randomized Controlled Trial

ABSTRACT

Background and Objective

Chronic nonspecific neck pain (CNNP) is highly prevalent, and exercise therapy is regarded as an effective intervention. Whole‐body vibration (WBV) may enhance neuromuscular activation and potentially improve muscle strength and endurance; however, evidence on its application in individuals with neck pain remains limited. This study aimed to compare the additive effects of WBV combined with exercise therapy versus exercise therapy alone on pain, disability, cervical muscle strength, and endurance in individuals with CNNP.

Materials and Methods

In this single‐blinded randomized clinical trial, 24 participants aged 25–50 years with CNNP were randomly assigned to the experimental group (6‐week home‐based routine exercise therapy + WBV) or the control group (6‐week home‐based routine exercise therapy alone) (n = 12 each). WBV was delivered through 18 supervised sessions, three sessions per week for 6 weeks. Outcome measures included pain (VAS), disability (Neck Disability Index), cervical flexor and extensor strength (handheld dynamometer), and muscle endurance (Harris test). Assessments were performed at baseline and after 6 weeks using the interventions. Paired t‐tests were used for within‐group comparisons, and ANCOVA for between‐group analyses at a significance level of 0.05.

Results

Both groups demonstrated significant within‐group improvements in pain, disability, and cervical muscle performance over the 6‐week intervention period (p < 0.001). Compared with the control group, the experimental group showed greater post‐intervention reductions in pain (11.20 ± 6.07 vs. 18.60 ± 9.06 mm; p = 0.002; partial η ² = 0.321) and disability (11.20 ± 4.34 vs. 15.46 ± 4.06%; p = 0.027; partial η ² = 0.252), as well as greater improvements in cervical flexor strength (5.60 ± 0.71 vs. 4.90 ± 0.37 N; p = 0.006; partial η ² = 0.311) and flexor endurance (78 ± 28 vs. 47 ± 12 s; p < 0.001; partial η ² = 0.381). No significant between‐group differences were observed for cervical extensor strength or endurance (p > 0.05).

Conclusion

Adding WBV to routine exercise therapy may provide short‐term additional benefits in pain, disability, and cervical flexor performance in individuals with CNNP. However, these preliminary findings should be interpreted cautiously due to the small sample size, absence of follow‐up assessment, and supervision differences between groups.

1. Introduction

Chronic nonspecific neck pain (CNNP) is a highly prevalent musculoskeletal disorder worldwide [1] and a major contributor to pain, disability, reduced quality of life, work absenteeism, and healthcare burden [2]. In addition to pain, individuals with CNNP commonly demonstrate cervical muscle weakness, neuromuscular control deficits, impaired proprioception, and reduced sensorimotor function, all of which may contribute to symptom persistence and functional limitations [3, 4].

Current conservative management approaches typically include exercise therapy, physiotherapy, motor control training, postural correction, and ergonomic education [5, 6]. Exercise therapy—particularly cervical muscle strengthening and cervical spine stabilization exercises—is considered one of the most commonly prescribed and evidence‐based treatments for neck pain, with several studies reporting its beneficial effects on pain reduction, functional improvement, and enhanced muscular endurance [7, 8, 9, 10]. Recent randomized controlled trials have also demonstrated beneficial effects of structured exercise‐based interventions, including elastic resistance exercise and back school‐based programs, on pain reduction and functional improvement in individuals with nonspecific neck pain [11, 12, 13]. However, responses to exercise therapy are not uniform across patients, and some studies have highlighted variability in treatment outcomes, limited long‐term effects, and the need for adjunctive strategies to enhance therapeutic efficacy [7].

In recent years, whole‐body vibration (WBV) has emerged as a novel rehabilitative modality [14]. WBV is suggested to enhance deep mechanoreceptor stimulation, increase muscle spindle activity, facilitate neuromotor pathways, and improve motor unit recruitment, potentially leading to improved strength, endurance, motor control, and proprioception [15]. Evidence from lower‐limb and lumbopelvic studies indicates that WBV can improve muscle strength, balance, and pain [16, 17], and several systematic reviews have confirmed that adding WBV to exercise therapy may yield additional benefits in individuals with chronic low back pain [14, 18].

However, despite the relatively large number of studies conducted on the lower limbs and lumbar region [14, 16, 17, 18], research investigating the effects of WBV on cervical musculature—particularly strength and endurance of the neck flexors and extensors—remains scarce. Most existing studies have primarily focused on local vibration therapy as an adjunct intervention for managing neck pain [19, 20], while limited evidence is available regarding the effects of broader vibration‐based approaches, such as WBV, on chronic neck pain, functional disability, and cervical muscle performance [21]. Unlike local vibration therapy, which applies mechanical stimulation directly to a targeted anatomical region, WBV delivers vibration through a larger kinetic chain and may induce broader neuromuscular activation via weight‐bearing postures and sensorimotor stimulation. Therefore, findings from local vibration studies cannot be directly generalized to WBV interventions, particularly in cervical rehabilitation.

Given the essential role of deep cervical muscles in maintaining spinal stability, sensorimotor control, and pain modulation, interventions that can augment the effectiveness of exercise therapy may offer meaningful clinical benefits. As exercise therapy is widely regarded as a core treatment for CNNP, integrating complementary modalities such as WBV may enhance neuromuscular responses and improve clinical outcomes. In the present study, WBV was delivered using an anterior push‐up stance, in which participants transmitted vibration through the upper extremities while maintaining cervical and trunk alignment. This posture was expected to preferentially increase loading demands on the anterior stabilizing musculature, particularly the deep and superficial cervical flexors, due to their role in maintaining head and neck stability against gravity and transmitted oscillatory forces. Therefore, the present study aimed to compare the additive effects of WBV combined with exercise therapy versus exercise therapy alone on pain, disability, and cervical muscle strength and endurance in individuals with CNNP. The findings of this study may provide new evidence supporting the use of WBV as an adjunct modality in cervical rehabilitation programs. We hypothesized that participants receiving WBV in addition to routine exercise therapy would demonstrate greater improvements in pain, disability, cervical muscle strength, and endurance compared with those receiving exercise therapy alone.

2. Materials and Methods

2.1. Study Design

This study was a randomized, single‐blinded clinical trial, prospectively registered in the Iranian registry of clinical trials prior to participant enrollment (registration number: IRCT20250119064442N1), and the Ethics committee of Shahid Beheshti University of Medical Sciences approved all protocols (IR.SBMU.RETECH.REC.1403.033). The assessor and the therapist were different individuals, and the assessor was blinded to group allocation throughout the study. Participant recruitment and data collection were conducted between May 2025 and September 2025.

2.2. Sample Size Calculation

As no previous randomized clinical trial with a similar methodology was available, an a priori pilot study was first conducted using five participants in each group. Pain intensity (VAS) was considered the primary outcome for sample size estimation. Based on pilot data and using the sample size formula for comparison of two independent means (formula shown below), the expected effect size was estimated from the observed between‐group difference and pooled standard deviation.

Assuming a two‐tailed alpha level of 0.05, statistical power of 90% (β = 0.10), and the estimated variance obtained from the pilot study (SD = 11), the required sample size was calculated as 12 participants per group. Therefore, a total sample size of 24 participants was considered sufficient for this preliminary randomized controlled trial.

$$n=\frac{{\left(z_{1-\frac{\alpha }{2}}+z_{1-\beta }\right)}^2\left({\delta }_1^2+{\delta }_2^2\right)}{{\left({\mu }_1-{\mu }_2\right)}^2}$$

2.3. Participants

Participants were recruited through convenience sampling from rehabilitation clinics and hospitals affiliated with medical universities across Tehran. The inclusion criteria were: adult age ranged between 25 and 50 years, diagnosis of CNNP (defined as neck pain without an identifiable specific pathology) for more than 12 weeks, pain intensity between 3 and 6 on the VAS scale, ability to perform light physical activity, no history of cervical spine surgery, absence of clinically observable postural abnormalities, determined through physiotherapist clinical inspection, including evident thoracic kyphosis, scoliosis, or forward head posture that could interfere with exercise performance or outcome assessment, no severe dizziness or reported vestibular disorders, and no major musculoskeletal problems in the upper extremity. Exclusion criteria included: lack of cooperation during training sessions, inability to tolerate vibration exposure, and absence from more than two intervention sessions. Inability to tolerate vibration exposure was defined as the occurrence of dizziness, nausea, headache, discomfort, or any symptom leading the participant to request termination of the session.

2.4. Procedure

After screening based on the inclusion criteria and obtaining informed consent, baseline outcome measures—including neck pain intensity, cervical muscle strength and endurance, and neck‐related disability—were recorded before the intervention. After baseline assessment, participants were randomly assigned to either the experimental or control group using a simple dice‐rolling procedure performed by an independent researcher who was not involved in participant recruitment, outcome assessment, or intervention delivery. If the rolled number was odd, the participant was allocated to the experimental group; if even, to the control group. Group assignment was communicated only to the treating physiotherapist after baseline measurements had been completed. The outcome assessor remained blinded to group allocation throughout the study, and participants were instructed not to disclose their assigned intervention during follow‐up assessments. Because allocation was generated individually after baseline assessment by an independent researcher and was not accessible to the recruiter or assessor beforehand, assignment could not be predetermined or manipulated.

The control group received the routine exercise therapy program, which was taught and demonstrated by a physiotherapist at the initial session and then performed independently at home for 6 weeks. The experimental group performed the same home‐based exercise program and, in addition, completed 18 supervised WBV sessions (three sessions per week for 6 weeks) under the guidance of an experienced physiotherapist. At the end of the 6‐week intervention period, all outcome measures were reassessed using the same procedures as at baseline.

2.5. Outcome Measures

2.5.1. Pain

Pain intensity was quantified using the Visual Analogue Scale (VAS). This tool represents the individual's subjective perception of pain on a 100‐mm horizontal line, where 0 mm indicates “no pain” and 100 mm represents “the worst pain imaginable”. A change of approximately 15–20 mm on the 100‐mm VAS has been reported as the minimal clinically important difference (MCID) for individuals with chronic neck pain [22].

2.5.2. Neck‐Related Disability

Neck‐related disability before and after the intervention was assessed using the Neck Disability Index (NDI). This questionnaire was translated and culturally adapted into Persian by Mousavi et al. in 2007, and its psychometric properties have been reported to be highly satisfactory, with a Cronbach's alpha of 0.88 and an ICC ranging from 0.92 to 0.97. The NDI consists of 10 items, of which seven assess activities of daily living, two assess pain intensity, and one evaluates concentration. Each item is scored on a 0–5 scale, producing a total score ranging from 0 to 50, where higher scores indicate greater disability. Disability severity is categorized as follows: 0–4 (0%–8%): no disability, 5–14 (10%–28%): mild disability, 15–24 (30%–48%): moderate disability, 25–34 (50%–64%): severe disability, and 35–50 (70%–100%): complete disability [23]. For the NDI, an improvement of approximately 5 points (or 10%) has been suggested as the minimal clinically important difference in patients with chronic neck pain [22].

2.5.3. Cervical Muscle Strength Assessment

Cervical muscle strength was evaluated using a handheld dynamometer [24]. The device used was a Camous handheld dynamometer (Camous Company, Iran), with a measurement accuracy of 0.1 kg and a maximum measurable force of 2000 N. Handheld dynamometry has previously demonstrated acceptable to excellent reliability for assessing cervical muscle strength in individuals with and without chronic neck pain when standardized testing positions are used [24].

2.5.3.1. Assessment of Cervical Extensor Strength

For the extensor strength test, participants were positioned prone, with the craniocervical region placed in slight passive flexion to minimize compensatory or undesired movements during cervical muscle contraction. To ensure proper execution, each participant was first familiarized with the task by performing five active cervical extension movements under the examiner's guidance. Depending on the participant's morphology, stabilization was provided by securing the upper thoracic region—either around the T4 spinous process or slightly above the thoracic kyphosis—against the edge of the table to prevent compensatory trunk movements. The dynamometer was then securely positioned over the external occipital protuberance, ensuring that it remained aligned horizontally.

Once proper positioning of both the participant and the dynamometer was confirmed, the procedure was explained. Participants were instructed to first apply an estimated submaximal contraction of approximately 50% of their perceived maximum for 6 s. After a 1‐min rest, they were asked to gradually increase force against the dynamometer to reach their maximum voluntary effort within 3 s, and then maintain maximal pressure for an additional 3 s.

To reduce anxiety or apprehensive movements, participants were reassured regarding the safety of the testing procedure. Each participant performed three maximal isometric voluntary contractions (MIVCs), with 1‐min intervals of rest between trials. After each trial, participants were asked whether they felt they had reached their true maximal contraction, to ensure maximal effort was obtained.

2.5.3.2. Assessment of Cervical Flexor Strength

For the flexor strength test, participants lay in a supine position and were instructed to slightly lift their head while maintaining a chin‐tucked posture. The flat surface of the dynamometer was placed against the participant's forehead to measure the isometric flexion force.

After confirming proper setup and alignment, the test procedure was explained. Participants first performed an estimated 50% submaximal contraction for 6 s, followed by a 1‐min rest. They were then instructed to gradually apply pressure with their head and neck against the dynamometer to reach maximal force within 3 s, and maintain it for another 3 s, similar to the extensor protocol. Participants performed three MIVC trials, with 1‐min rest intervals between attempts.

2.5.4. Cervical Muscle Endurance

Both cervical flexor and extensor endurance tests were performed according to previously described standardized protocols reported by Harris et al. [25].

2.5.4.1. Cervical Flexor Endurance Test

This test was performed in a crook‐lying position (supine with knees flexed). Operationally, the participant was instructed to perform a maximal chin tuck and then lift the head and neck until the head was approximately 2.5 cm (1 inch) above the surface of the table, while maintaining the chin‐tucked position. Once the target position was achieved, a horizontal reference line was drawn across the skin folds on the anterior neck. The assessor placed their left hand beneath the participant's occiput to monitor any loss of position.

Verbal cues (e.g., “keep your chin tucked” or “hold your head up”) were provided if the anterior neck skinfolds began to separate or if the participant's head lightly contacted the assessor's hand. The test was terminated if the skin folds no longer approximated—indicating loss of chin tuck—or if the participant's head rested on the assessor's hand for more than 1 s. A stopwatch was used to record the duration (in seconds) for which the participant was able to maintain the required position.

2.5.4.2. Cervical Extensor Endurance Test

Participants lay prone on a table with the head and cervical spine unsupported and extended beyond the table's edge. The head was positioned in a neutral sagittal alignment. A weight of 1.5 kg for women and 2 kg for men was placed on the back of the head. Participants were instructed to maintain the head in a steady, neutral position with a slight chin tuck to align the cervical spine in a zero‐degree neutral posture (visually confirmed).

The test duration, representing cervical extensor endurance, was recorded in seconds using a stopwatch. The test was terminated if the weight touched the ground or if the cervical spine deviated more than 5° from the horizontal plane.

2.6. Routine Exercise Therapy

The participants in both groups performed a structured routine exercise therapy program for 6 weeks, as outlined in Table 1. After receiving initial instruction and technique correction by an experienced physiotherapist, participants continued the exercises independently at home throughout the intervention period. Participants in both groups received the same initial instruction session, including exercise demonstration, supervised practice, and technique correction before beginning the home‐based program. The program consisted of progressive cervical rehabilitation exercises, including isometric resistance exercises in four directions (right side, left side, forehead, and behind the head), active cervical range‐of‐motion exercises (flexion–extension and right–left rotation), deep cervical flexor activation through chin‐tuck holds, prone neck‐lift exercises, bilateral upper‐limb elevation in A, Y, T, and W positions, and postural training using visual feedback with a mirror to maintain corrected head and neck alignment. All exercises were performed in a fixed sequence and progressed weekly according to Table 1. Exercise progression was standardized according to the predefined weekly protocol and was not individually modified during the intervention period, as no participants reported exercise‐related symptoms requiring protocol adjustment. Participants in both groups were instructed to perform the home‐based exercise program three sessions per week for 6 weeks. Each session lasted approximately 20–25 min, depending on individual pace and rest intervals. To monitor adherence to the home‐based exercise program, participants were instructed to record completion of each exercise session in a self‐report log and were contacted weekly by the physiotherapist to encourage compliance and address any questions regarding exercise performance.

Table 1.

Routine therapy exercise.

Neck rehabilitation exercises (all exercises were performed in the same sequence in each session)	Training week	Repetitions	Exercise duration (s)	Rest duration (s)
Placing the right hand beside the head and applying isometric resistance	1	5	8	10
Placing the left hand beside the head and applying isometric resistance	1	6	8	10
Placing both palms on the forehead and applying isometric resistance	1	7	8	10
Placing both palms behind the head and applying isometric resistance	1	8	10	10
Neck flexion and extension	2	8	12	15
Neck rotation to the right and left within the standard range of motion	2	9	15	15
Chin tuck (deep cervical flexor activation), holding the position for 10 s	3	10	15	15
Prone lying with neck lifted from the floor	4	10	15	15
Bilateral arm elevation and holding for 10 s in four positions (A, Y, T, W)	5	10	15	15
Using a mirror in front and beside the participant to correct head posture and holding the corrected posture for 20 s	6	10	20	10

2.7. WBV

In the experimental group, in addition to performing the routine therapeutic exercises described for the control group, WBV was applied for 18 supervised sessions over 6 weeks (three sessions per week). WBV was delivered using a FitVibe Excel Pro platform (GymnaUniphy, Belgium), a vertical synchronous oscillating vibration device designed for rehabilitation applications. Vibration was applied at a frequency of 50 Hz and an amplitude of 1.53 mm. Before participation, all individuals were screened for contraindications to vibration exposure, including vestibular disorders, severe dizziness, recent musculoskeletal injury, and inability to tolerate vibration‐based exercise. For WBV exposure using a three‐level synchronous oscillating/vibratory platform, participants were positioned in a push‐up stance, ensuring that their feet remained on the floor and that excessive lumbar lordosis or thoracic kyphosis was avoided.

The angles between the pelvis and trunk and between the upper limbs and trunk were measured using a handheld goniometer. Additionally, the distance between the hand placement on the platform and the tips of the feet was measured using a tape measure to ensure consistent positioning across all training sessions. The head and neck were kept in alignment with the trunk, and participants maintained visual focus on a fixed point marked at the center of the platform (Figure 1).

Figure 1.

Participant position during WBV intervention in the push‐up stance, with standardized neutral spinal alignment and controlled body positioning throughout sessions.

During each session, participants were exposed to vibration for four sets of 30 s, with 30 s of rest between sets. The vibration parameters remained constant throughout the 6‐week intervention period and were not progressively modified. The vibration parameters remained constant throughout the 6‐week intervention period and were not progressively modified. These parameters were selected based on prior WBV studies demonstrating that vibration frequency and body position influence neuromuscular responses, muscle activation, and motor unit behavior during weight‐bearing vibration exposure [15, 26].

Participants were monitored throughout all WBV sessions for adverse responses. No adverse events or serious intolerance to vibration exposure were reported during the intervention period.

2.8. Statistical Analyses

Statistical analyses were performed using SPSS software version 20 at a significance level of 0.05. The Shapiro–Wilk test was used to assess the normality of the data distribution. In addition to normality assessment using the Shapiro–Wilk test, assumptions for ANCOVA, including homogeneity of regression slopes and linearity between covariates and dependent variables, were examined before analysis. No major violations of model assumptions were detected. Given that the data were normally distributed, paired t‐tests were applied for within‐group pre‐ and post‐intervention comparisons. Analysis of covariance (ANCOVA) was used to compare the two groups after the intervention. In this analysis, all baseline values were entered as covariates, and the post‐intervention outcomes were compared between the two groups while controlling for their pre‐intervention scores. In addition to p values, effect sizes (Cohen's d for within‐group comparisons and partial η ² for ANCOVA analyses) were calculated to quantify the magnitude of observed effects.

3. Results

A total of 24 individuals with CNNP completed the study and were included in the analysis, comprising 12 participants in the experimental group (mean age: 34.6 ± 5.40 years) and 12 in the control group (mean age: 35.8 ± 4.68 years). Participant flow throughout the study is presented in the CONSORT flow diagram (Figure 2). A total of 32 individuals were screened for eligibility, 24 met the inclusion criteria and were randomized, and all randomized participants completed the intervention and post‐intervention assessment and were included in the final analysis. Adherence to the intervention protocol was considered satisfactory, as all participants completed the 6‐week intervention period and attended the post‐intervention assessment. Participants in the experimental group completed all scheduled supervised WBV sessions. No participant withdrew from the study because of poor adherence or noncompliance with the prescribed intervention protocol. No adverse events, symptom exacerbation, or intervention‐related intolerance were reported throughout all WBV sessions. Home exercise adherence was monitored using participant self‐report logs and weekly follow‐up; however, exact adherence percentages were not systematically quantified. Also, no major protocol deviations were identified during the intervention period.

Figure 2.

CONSORT flowchart.

Each group included 6 men and 6 women. Table 2 shows the mean age, weight, BMI, and pain intensity before the therapeutic interventions in two groups. The normality results demonstrated a normal distribution for all outcome measures (p > 0.05). Baseline comparisons revealed no significant differences between groups across all outcome measures before the intervention (p > 0.05, Table 4).

Table 2.

Comparison of demographic characteristics in the two groups.

Variables	Control group, n:12 (mean ± SD)	Experimental group, n:12 (mean ± SD)	p value
Age (year)	35.68 ± 4.68	34.60 ± 5.40	0.18
Weight (kg)	72.42 ± 6.64	70.50 ± 6.28	0.83
Body mass index (kg/m2)	23.60 ± 1.87	23.86 ± 1.66	0.74
Pain (mm)	46.60 ± 6.07	45.66 ± 6.60	0.65

Table 4.

Comparison of baseline and post‐intervention outcome measures between the control and experimental groups.

Variables	Baseline p value (between‐group pre‐intervention comparison)	Control group, n:12	Experimental group, n:12	p value (between‐group comparison)	Effect size (partial η 2)
		Post‐intervention (mean ± SD)	Post‐intervention (mean ± SD)
Pain (mm)	0.554	18.60 ± 9.06	11.20 ± 6.07	0.002*	0.361
Disability (%)	0.09	15.46 ± 4.06	11.20 ± 4.34	0.027*	0.252
Extensor strength (N)	0.880	6.70 ± 0.17	6.60 ± 1.61	0.07	0.148
Flexor strength (N)	0.246	4.90 ± 0.37	5.60 ± 0.71	0.006*	0.311
Extensor endurance (s)	0.953	182 ± 104	171 ± 74	0.09	0.131
Flexor endurance (s)	0.755	47 ± 12	78 ± 28	< 0.001**	0.437

^* p < 0.05

^** p < 0.001.

3.1. Within‐Group Pre‐ and Post‐Intervention Comparison

The results of within‐group comparisons are presented in Table 3. A significant reduction in mean pain scores (p < 0.001) and disability levels (p < 0.001) was observed in both the experimental and control groups after the 6‐week intervention period compared with baseline. Additionally, cervical muscle strength for both the flexors and extensors increased significantly in both groups following the intervention (p < 0.001). Cervical extensor endurance showed a significant improvement in the experimental group after 6 weeks (p = 0.001); however, no significant change in extensor endurance was observed in the control group between pre‐ and post‐intervention assessments (p = 0.30).

Table 3.

Mean, standard deviation, and level of significance in outcome measures for within‐group pre‐ and post‐intervention comparison.

	Control group, n:12				Experimental group, n:12
Variables	Pre‐intervention (mean ± SD)	Post‐intervention (mean ± SD)	p value (within‐group comparison)	Cohen's d	Pre‐intervention (mean ± SD)	Post‐intervention (mean ± SD)	p value (within‐group comparison)	Cohen's d
Pain (mm)	46.60 ± 6.07	18.60 ± 9.06	< 0.001**	2.63	45.66 ± 6.60	11.20 ± 6.07	< 0.001**	3.44
Disability (%)	35.20 ± 2.08	15.46 ± 4.06	< 0.001**	2.87	32.10 ± 3.22	11.20 ± 4.34	< 0.001**	3.14
Extensor strength (N)	5.30 ± 0.76	6.70 ± 0.17	< 0.001**	1.76	4.60 ± 0.44	6.60 ± 1.61	< 0.001**	3.06
Flexor strength (N)	4.20 ± 1.11	4.90 ± 0.37	< 0.001**	2.25	3.80 ± 1.82	5.60 ± 0.71	< 0.001**	2.90
Extensor endurance (s)	168 ± 99	182 ± 104	0.03*	1.45	121 ± 85	171 ± 74	< 0.001**	2.29
Flexor endurance (s)	31 ± 14	47 ± 12	< 0.001**	1.86	35 ± 34	78 ± 28	< 0.001**	2.70

^* p < 0.05

^** p < 0.001.

3.2. Between‐Group Post‐Intervention Comparison

The results of between‐group comparisons are presented in Table 4. The findings demonstrated that, after the intervention, the experimental group experienced significantly greater reductions in pain (p = 0.002) and disability (p = 0.027), along with significantly greater increases in cervical flexor strength (p < 0.001) and cervical flexor endurance (p < 0.001), compared with the control group (Table 4). No significant differences were observed between the two groups regarding the cervical extensor strength or cervical extensor endurance (p > 0.05).

4. Discussion

This study aimed to investigate whether adding WBV to routine exercise therapy provides additional clinical benefits in individuals with CNNP. In this context, both study arms experienced significant within‐group improvements in pain, disability, and cervical muscle performance after the 6‐week intervention period— confirming that a supervised cervical exercise program is effective in CNNP. This is consistent with previous randomized trials demonstrating that structured exercise interventions can improve pain and functional outcomes in individuals with nonspecific neck pain [11, 12, 13]. The significant gains in muscle strength and endurance in both groups likely reflect increased muscle capacity, enhanced neuromuscular coordination, and reduced pain‐related inhibition, consistent with prior literature that supports exercise therapy as a first‐line non‐surgical intervention for neck pain [7, 8, 9, 10].

The experimental group (exercise + WBV) showed additional benefit over the control group by achieving greater reductions in pain and disability, and superior improvements in cervical flexor strength and endurance. In addition to statistical significance, the observed improvements in pain and disability should be interpreted in light of their potential clinical relevance, as previously reported MCID thresholds for VAS and NDI in individuals with chronic neck pain suggest that changes of approximately 15–20 mm and 5 points, respectively, may be clinically meaningful. Although effect size estimates were generally small to moderate, the consistent direction of improvements across pain, disability, and cervical flexor outcomes suggests that the additional effects of WBV may be clinically relevant and warrant further investigation in larger trials. This suggests that WBV may augment the therapeutic effects of exercise by enhancing sensorimotor input, increasing muscle spindle activation, and facilitating greater motor unit recruitment during and after vibration exposure. These findings align with prior vibration‐based interventions in cervical disorders: for example, a randomized trial showed that adding local vibration to physiotherapy improved pain, proprioception, and disability in cervical disc herniation [19], and another study reported reductions in pain, disability, and pressure–pain sensitivity in CNNP following vibration therapy [27]. Together, these findings are consistent with the concept that vibration‐enhanced sensorimotor stimulation—whether local or whole‐body—can augment conventional exercise‐based rehabilitation, which aligns with the improvements observed in the experimental group.

Furthermore, systematic reviews and meta‐analyses in musculoskeletal conditions (though primarily lower back or limb studies) have demonstrated that WBV combined with exercise can yield additional improvements in pain, function, and motor performance compared to exercise alone, without serious adverse effects [14, 28, 29]. These benefits are commonly attributed to WBV‐induced increases in muscle spindle sensitivity, enhanced afferent input, modulation of spinal reflex excitability, and improved motor‐unit recruitment efficiency—mechanisms widely described in neuromuscular studies of vibration exposure [15, 26, 30]. Therefore, the additional benefits observed in the present study may be explained, at least in part, by these physiological mechanisms, which may amplify the effects of routine exercise therapy. These findings support the potential of WBV as a non‐invasive adjunct modality in rehabilitation, and align with our observed enhancements in clinical and performance outcomes for flexor muscles and disability.

A notable finding of the present study was the absence of significant between‐group differences in cervical extensor strength or endurance. This selective pattern may be explained by several physiological and methodological factors. First, the push‐up stance used during WBV likely directed vibratory forces predominantly through the upper limbs and anterior trunk toward the anterior cervical musculature, resulting in greater activation of flexors than extensors. Prior electromyographic studies confirm that WBV‐induced muscle activation strongly depends on posture, weight‐bearing configuration, and contact points [26, 31, 32]. Second, the cervical extensor group contains a higher proportion of postural, slow‐twitch fibers optimized for tonic control and endurance [33, 34, 35], which may respond less readily to short‐duration, high‐frequency vibration compared with the more phasic and stabilizing flexor muscles. Accordingly, the WBV parameters used in this study may have been sufficient to improve flexor performance but insufficient to elicit measurable changes in posterior cervical musculature within 6 weeks. Methodological considerations—including the sensitivity of extensor strength/endurance assessments to small deviations in head posture and stabilization—may also increase measurement variability and reduce the ability to detect small between‐group differences, particularly with a modest sample size. Future studies employing alternative postures, longer intervention durations, or progressive WBV loading may better target the extensor musculature.

Overall, the current results expand the limited evidence for WBV application in cervical spine rehabilitation, demonstrating that when properly combined with exercise therapy and using an anterior‐body stance, WBV can yield additional benefits for flexor muscle performance and global neck disability. This aligns with growing interest in vibration‐based therapies—both local and whole‐body—in neck pain rehabilitation, and supports the inclusion of WBV as an adjunct to conventional exercise. However, the applicability of these findings to the broader population of individuals with CNNP should be interpreted with caution. The relatively restrictive eligibility criteria, including the exclusion of individuals with common coexisting postural and musculoskeletal conditions, may limit the generalizability of the present findings to routine clinical practice.

Although the experimental group demonstrated superior improvements in several outcomes, these findings should not be interpreted as evidence that the observed between‐group differences were attributable solely to the specific physiological effects of WBV. Because participants in the WBV group received 18 supervised treatment sessions in addition to the home exercise program, whereas the control group performed only home‐based exercises, differences in therapist contact, supervision, motivation, and treatment expectations may also have contributed to the observed benefits. Therefore, the additional effects observed in this study likely reflect the combined influence of WBV and nonspecific contextual factors rather than WBV alone. In addition, because this was a preliminary trial with a small sample, the estimated between‐group effect sizes should be interpreted with caution. Small studies are more susceptible to imprecise effect estimates and may overestimate treatment effects; therefore, confirmation in adequately powered randomized trials is required before firm conclusions can be drawn. Furthermore, because outcomes were assessed only immediately after completion of the 6‐week intervention, the persistence of the observed improvements beyond the treatment period remains unknown. Consequently, it cannot be determined whether the additional benefits associated with WBV represent only short‐term benefits or are sustained over longer follow‐up periods.

5. Limitations and Suggestions

The study's main limitations include a relatively small sample size, which may have limited the power to detect modest effects (particularly for extensor outcomes), the absence of follow‐up assessment beyond the immediate post‐intervention period which limits interpretation of the durability of treatment effects and precludes determination of whether the observed improvements were maintained after completion of the intervention, and the use of a single WBV posture (push‐up stance) which may have preferentially increased anterior cervical loading. Although both groups performed the same home‐based exercise program, the experimental group additionally received supervised WBV sessions, resulting in greater therapist contact and supervision, which may have influenced motivation, adherence, and other nonspecific treatment effects. Furthermore, the study did not include a sham vibration group. Consequently, it was not possible to distinguish the specific physiological effects of WBV from nonspecific contextual effects, such as therapist attention, participant expectations, or placebo responses. In addition, home exercise adherence was monitored but not systematically quantified or compared between groups. The study also evaluated multiple clinical outcomes without a single prespecified primary endpoint, which increases the risk of multiplicity and type I error inflation. Finally, the study population was restricted to adults aged 25–50 years with CNNP and excluded individuals with several common coexisting postural or musculoskeletal features (e.g., forward head posture, spinal postural abnormalities, and upper‐extremity musculoskeletal complaints). These criteria may limit the external validity and generalizability of the findings to the broader population of individuals with CNNP commonly encountered in clinical practice.

Future research should include larger and more diverse trials, longer follow‐up periods, and compare multiple WBV postures (e.g., standing, supine, prone) to determine optimal protocols for targeting different cervical muscle groups (flexors vs. extensors). The integration of objective neuromuscular assessments (e.g., surface EMG, muscle cross‐sectional area via ultrasound, proprioceptive tests) would help elucidate underlying mechanisms of adaptation. Comparative studies of local vibration therapy versus WBV, and investigations of progressive WBV dose (frequency, amplitude, duration) and periodization strategies, are warranted. Finally, future randomized trials incorporating sham vibration conditions are warranted to better isolate the true treatment effect of WBV.

6. Conclusion

In conclusion, both groups demonstrated significant within‐group improvements following the 6‐week intervention period. Participants receiving WBV in addition to routine exercise therapy showed greater improvements in pain, disability, cervical flexor strength, and flexor endurance compared with exercise alone, whereas extensor outcomes did not significantly differ between groups. These findings suggest that WBV may provide short‐term additional benefits as an adjunct to exercise therapy in individuals with CNNP. However, the results should be interpreted cautiously, given the small sample size, absence of follow‐up assessment beyond the immediate post‐intervention period, imbalance in supervision and therapist contact between groups, lack of a sham vibration control, and limited generalizability due to restrictive eligibility criteria. Larger and better‐controlled trials with longer follow‐up are warranted.

Author Contributions

Fatemeh Arghon: methodology, writing – original draft. Hoda Niknam: conceptualization, supervision, project administration, writing – review and editing. Khosro Khademi Kalantari: methodology, writing – review and editing. Alireza Akbarzadeh Baghban: formal analysis, data curation.

Funding

The authors have nothing to report.

Ethics Statement

This study was approved by the ethics committee of Shahid Beheshti University of Medical Sciences with the code IR.SBMU.RETECH.REC.1403.033 and registered in the Iranian Register of Clinical Trials (registration number: IRCT20250119064442N1).

Consent

Written informed consent or assent (as appropriate) was obtained from all participants and their legal guardians.

Conflicts of Interest

The authors declare no conflicts of interest.

Transparency Statement

Hoda Niknam affirms that this manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned have been explained.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.