Impact of Corrective Exercise Training on Work-Related Neck and Shoulder Musculoskeletal Disorders and Quality of Life in Manufacturing Workers

Abstract

Context:

Work-related musculoskeletal disorders (WMSDs), especially in the neck and shoulder, are common among manufacturing workers and negatively affect quality of life (QoL) and productivity.

Aims:

To assess the effectiveness of an 8-week corrective exercise program in reducing neck and shoulder WMSDs and improving QoL in industrial workers.

Settings and Design:

A quasi-experimental study was conducted at a cable and wire factory in Iran.

Methods and Materials:

Forty male workers with WMSDs were assigned to either an intervention (n = 20) or a control (n = 20) group. The intervention group participated in supervised corrective exercises based on the Movement Direction Control model, three times per week for eight weeks. Outcomes were measured using the Nordic Musculoskeletal Questionnaire (NMQ) and the Short Form-36 (SF-36).

Statistical Analysis Used:

Descriptive statistics, analysis of covariance (ANCOVA), and multivariate analysis of covariance (MANCOVA) for musculoskeletal disorders and QoL dimensions were used. All analyses were performed using SPSS v22 (International Business Machines Cooperation (IBM)) with a significance level set at P < 0.05.

Results:

The intervention group showed significant improvement in neck and shoulder pain severity and QoL dimensions. ANCOVA and MANCOVA indicated statistically significant group differences (P < 0.001), with large effect sizes.

Conclusions:

Corrective exercise training appears effective in reducing neck and shoulder WMSDs and enhancing QoL among manufacturing workers. Integration of such programs into workplace health strategies is recommended.

INTRODUCTION

Work-related musculoskeletal disorders (WMSDs) are a significant occupational health challenge. Despite technological advancements, repetitive tasks and static postures in many sectors contribute to WMSDs,[1] affecting 76.1 million people worldwide[2] and leading to disability in numerous countries.[3] These disorders incur substantial costs, consuming 1%–2.5% of GNP in industrialized nations like the United States and United Kingdom,[4,5] and cause absenteeism and reduced productivity.[6]

The World Health Organization defines quality of life (QoL) as an individual’s perception of their life within their cultural context, goals, and expectations.[7] WMSDs negatively impact QoL, reducing physical, social, and psychological well-being.[8,9,10,11,12] WMSDs affect muscles, nerves, tendons, ligaments, and joints due to occupational activities.[13] Risk factors include non-modifiable elements (e.g. age, gender) and modifiable ones (e.g. poor biomechanics, low fitness, psychosocial stressors).[14] Shoulder and neck pain are particularly prevalent,[15,16] manifesting as discomfort, numbness, and restricted mobility.[17]

Physical activity enhances endurance and stability, reducing WMSD risk,[12,18] while excessive workplace demands increase exhaustion.[17,19] Corrective exercises, improving flexibility and posture, mitigate WMSDs and enhance QoL.[20,21,22,23,24] In Iran, neck discomfort is prevalent (66.7%) among handicraft workers,[15] yet manufacturing workers, with high WMSD rates (e.g. 41.2% in China),[2] remain understudied, warranting further research.

SUBJECTS AND METHODS

Participants

This study was conducted at Behfar Cable and Wire Factory in Damghan, Iran, in collaboration with the factory’s Occupational Medicine Department. From 389 eligible workers, 40 male employees with work-related musculoskeletal symptoms were selected based on specific criteria. Participants were randomly assigned to an intervention group receiving corrective exercise training (n = 20) and a control group (n = 20) placed on a waitlist.

Instruments

1. Short Form Health Survey (SF-36)

This study utilized the validated Persian version of the SF-36 questionnaire to assess health-related QoL. Although the SF-36 includes 36 items across eight subscales, the focus was placed on the two primary summary measures: Physical Health and Mental Health, which provide a broad overview of employees’ health status. This approach was chosen to streamline data analysis and align closely with the study’s objectives. The Persian version, validated by Montazeri et al.[25] (2005), demonstrated good reliability with a Cronbach’s alpha of 0.79.

2. Nordic Musculoskeletal Questionnaire (NMQ)

The Nordic Musculoskeletal Questionnaire (NMQ), developed in 1987 by Kuorinka et al.[26] at the Institute of Occupational Health in Scandinavia, is a validated tool for assessing musculoskeletal disorder prevalence. It includes 37 items covering demographics, pain intensity in nine body regions, and physical and cognitive demands over six months. In this study, the NMQ showed high reliability with a Cronbach’s alpha of 0.88.

Intervention program

The present study employed the Movement Direction Control Exercise approach developed by Comerford and Mottram,[27] which aims to correct uncontrolled cervical movements by retraining motor patterns and enhancing segmental stability. Participants performed slow and controlled exercises such as controlled head lifts, lateral neck flexion, thoracic flexion, scapular adduction, and cervical segmental movements, while maintaining proper alignment and minimizing compensatory actions. Sessions followed a structured protocol with a 1:1 work-to-rest ratio (and a 2:1 ratio between movements and set breaks), progressing weekly in terms of intensity and complexity. Exercises were conducted individually under expert supervision, three times a week for eight weeks, to improve neuromuscular control and reduce chronic neck pain through optimized motor behavior.[27] The detailed Movement Direction Control exercise protocol used in the present study is presented in Table 1.

Table 1.

Movement direction control exercises for shoulder and neck rehabilitation

Exercise	Corrective Movement	Target Muscles	Objective	Duration (Seconds/Repetitions)	Execution Principles
Chin Tuck	Slightly retract the head to align the neck	Deep neck flexors (DNF)	Improve cervical stability and reduce spinal pressure	20–30 s (3–5 reps)	Slow and controlled, without excessive pressure
Scapular Setting	Gently pull the scapulae backward and downward without elevating the shoulders	Rhomboids, lower trapezius, serratus anterior	Improve shoulder stability and reduce neck and scapular pain	20–30 s (3–5 reps)	Focus on activating stabilizing muscles
Thoracic Extension	Sit or stand upright while extending the thoracic spine	Spinal extensors	Correct cervical curvature and improve posture	15–20 s (3–4 reps)	Control movement without excessive cervical deviation
Controlled Shoulder Lifts	Lift arms to shoulder height without neck movement	Deltoid, rotator cuff, serratus anterior	Increase motor control of the neck and shoulders	10–15 reps per set (3 sets)	Emphasize movement control without excessive cervical contraction
Neck Flexion Control	Slightly tuck the chin and slowly flex the head forward	Cervical flexors and vertebral stabilizers	Improve motor control in the cervical region	15–20 s (3–5 reps)	Slow and fully controlled, avoiding excessive tension
Shoulder Retraction	Pull scapulae together without moving the head	Rhomboids, middle trapezius	Improve shoulder stability and reduce neck tension	15–20 s (3–5 reps)	Focus on active control of stabilizing muscles

Data analysis

Descriptive statistics, Kolmogorov-Smirnov tests for normality, and analysis of covariance (ANCOVA) were applied to analyze the pre- and post-intervention data. The significance level was set at P < 0.05. SPSS version 22 (International Business Machines Cooperation (IBM)) was used for data analysis.

Ethical considerations

The study was reviewed by the factory’s occupational health team in accordance with Iranian safety regulations. Participants gave written informed consent, and confidentiality was maintained. The study complied with the Declaration of Helsinki (2013).[28]

RESULTS

Table 2 outlines the demographic characteristics of the participants in both the experimental and control groups. All participants in the present study were male, which reflects the gender composition determined by the nature of the work and occupational demands.

Table 2.

Demographic characteristics of participants

Variable	Experimental Group Frequency (%)	Control Group Frequency (%)
Age
<30	3 (15%)	4 (20%)
31–35 years	5 (25%)	4 (20%)
36–40 years	4 (20%)	3 (15%)
41–45 years	8 (40%)	9 (45%)
Education Level
Primary School	2 (10%)	3 (15%)
Middle School	3 (15%)	4 (20%)
High School Diploma	5 (25%)	6 (12%)
Associate Degree	2 (10%)	2 (10%)
Bachelor’s Degree	7 (35%)	5 (25%)
Master’s Degree	1 (5%)	0 (0%)
Marital Status
Single	4 (20%)	5 (25%)
Married	15 (75%)	14 (70%)
Divorced	1 (5%)	1 (5%)
Work Experience
<5 years	2 (10%)	5 (25%)
5-15 years	8 (40%)	8 (40%)
>15 years	10 (50%)	7 (35%)

Table 3 presents descriptive statistics of research variables, indicating that only the experimental group showed significant improvement in musculoskeletal disorders and QOL post-intervention.

Table 3.

Descriptive dimensions of research variables in pre- and post-tests in terms of group

Variable	Dimension	Mean (SD)
		Pre-test		Post-test
		Control	Experimental	Control	Experimental
Musculoskeletal Disorders of the Shoulder and neck	Total	44.46 (6.61)	43.86 (6.93)	44.40 (5.72)	29.53 (6.52)
Quality of Life	Total	92.11 (3.30)	91.48 (2.90)	92.99 (3.10)	112.29 (2.30)
	Physical Health	45.53 (7.30)	44.50 (5.30)	45.69 (6.60)	55.50 (3.40)
	Mental Health	46.58 (2.50)	46.98 (4.20)	47.30 (2.70)	56.79 (3.00)

SD: Standard deviation

Figure 1 illustrates the pre- and post-intervention changes in musculoskeletal disorders and quality of life scores in the experimental and control groups.

Figure 1.

Comparison of pre- and post-intervention mean scores of musculoskeletal discomfort (NMQ), physical health, and mental health between experimental and control groups. Lower NMQ and higher QoL scores were observed in the intervention group. NMQ: Nordic Musculoskeletal Questionnaire; QOL: Quality of life

The multivariate analysis of covariance (MANCOVA) results in Table 4 demonstrated a significant overall effect of the corrective exercise training on combined dependent variables.

Table 4.

MANCOVA results for quality of life and neck-shoulder disorders controlling pre-test scores

Multivariate Test	Value	F	Hypothesis df	Error df	P	Partial η2
Pillai’s Trace	0.405	2.548	8	30	0.030	0.405
Wilks’ Lambda	0.346	2.548	8	30	0.030	0.405
Hotelling’s Trace	1.890	2.548	8	30	0.030	0.405
Roy’s Largest Root	1.890	2.548	8	30	0.030	0.405

MANCOVA: Multivariate analysis of covariance, DF= Degree of freedom, F= F-statistic( Fisher’s ratio)

Table 5 reports ANCOVA results for musculoskeletal disorders, revealing a significant reduction in post-test scores for the experimental group compared to the control group.

Table 5.

ANCOVA results for post-test scores of work-related neck and shoulder musculoskeletal disorders

Source	SS	df	MS	F	P
Pre-test	10,241.55	1	10,241.55	48.16	<0.0001
Group	4,039.60	1	4,039.60	18.99	<0.0001

ANCOVA=Analysis of Covariance, SS=Sum of Squares, DF= Degree of freedom, MS= Mean Square, F= F-statistic( Fisher’s ratio), P= P-value ( Probability Value), Patial Eta Squared

Adjusted means and standard errors reported in Table 6 illustrate the practical differences between groups, with the experimental group showing improvements in all measured outcomes.

Table 6.

Adjusted post-test means and standard errors for dependent variables by group

Variable	Group	Adjusted Mean	Standard Error
Neck and Shoulder Musculoskeletal Disorders	Experimental	29.50	0.90
	Control	44.30	0.80
Physical Health	Experimental	55.61	0.80
	Control	45.57	0.80
Mental Health	Experimental	56.26	0.90
	Control	47.87	0.90

Table 7 displays univariate ANCOVA findings for QOL dimensions, with significant effects on physical health and mental health, confirming the intervention’s positive impact.

Table 7.

Univariate ANCOVA results for quality-of-life dimensions

Variable	Dimension	Source	SS	df	MS	F	Sig.	η2	Statistical power
	Physical Health	Pre-test	256.13	1	256.13	10.14	0.007	0.420	0.841
Quality of Life		Group Membership	470.14	1	470.14	10.88	0.005	0.437	0.865
	Mental Health	Pre-test	201.13	1	201.13	3.20	0.085	0.101	0.215
		Group Membership	808.65	1	808.65	7.83	0.014	0.359	0.740

ANCOVA=Analysis of Covariance, SS=Sum of Squares, DF= Degree of freedom, MS= Mean Square, F= F-statistic( Fisher’s ratio), P= P-value (Probability Value), Patial Eta Squared, Sig. Significance

DISCUSSION AND CONCLUSION

This study examined the effectiveness of corrective exercise training in reducing neck and shoulder WMSDs and improving QoL among manufacturing workers. Participants in the intervention group reported significantly less musculoskeletal discomfort and better physical and mental health compared to the control group.

These findings are consistent with prior research. Alseminy et al.[1] (2022) emphasized the role of physical activity in relieving musculoskeletal pain, and Tahermanesh et al.[29] (2023) highlighted both physical and psychological improvements from similar interventions. Our results reinforce the dual benefits of corrective exercises in occupational settings.

Due to the high prevalence of WMSDs and their effects on absenteeism and productivity, implementing these programs can enhance employee health and organizational performance. Additionally, as workers from lower socioeconomic backgrounds are disproportionately affected, accessible and equitable interventions are crucial.[30] Because WMSDs result from multiple modifiable and non-modifiable factors, a multidimensional approach that integrates exercise with ergonomic and psychosocial strategies is recommended for optimal outcomes.

Limitations include small sample size, short duration, and lack of long-term follow-up. Future research should address these gaps to better assess the sustained impact of corrective exercise interventions. In conclusion, corrective exercise training is an effective and practical strategy to improve musculoskeletal and overall health among industrial workers and should be integrated into workplace health programs.

Key messages

Corrective exercise training reduces neck and shoulder musculoskeletal disorders and improves physical and mental health in industrial workers. Structured exercise programs in occupational health can enhance well-being and reduce absenteeism in high-risk manufacturing settings.

Author contributions

Azin Taghipour (AZ) and Sara Eyni (SE) jointly conceptualized and designed the study and defined its intellectual content, with AZ supervising the research process. SE also managed data acquisition, experimental execution, data analysis, and statistical interpretation. Mohsen Khalili (MK), the Corresponding Author, conducted the literature review, prepared and edited the manuscript, and critically reviewed it for intellectual content. All authors approved the final manuscript.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.