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Work-Related Musculoskeletal Disorders among Public Bus Drivers in Kerala: A Cross-Sectional Study Linking Ergonomic Strain to Road Safety Risk

This cross-sectional study of 405 Kerala bus drivers reveals an alarmingly high prevalence of work-related musculoskeletal disorders, particularly in the lumbar region, which is significantly associated with excessive daytime sleepiness, shorter sleep duration, and excessive working hours, thereby linking ergonomic strain to increased road safety risks.

Original authors: ARUN CHAND, A B Bhasi

Published 2026-07-07

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: ARUN CHAND, A B Bhasi

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine a fleet of public buses in Kerala, India, as a giant, moving office where the "desk" is a driver's seat and the "work" is steering a heavy vehicle for hours on end. This study looked at 405 of these drivers to see how their bodies are holding up under the pressure of the job.

Here is the story of what they found, told simply:

1. The "Wear and Tear" is Everywhere

Think of the human body like a car. If you drive a car over rough roads for 10 hours a day without changing the oil or checking the tires, parts will eventually break. The researchers found that these bus drivers are experiencing exactly that kind of "wear and tear," but on their bodies.

The Back is the Strained Engine: The most damaged part is the lower back (lumbar region). About 72% of the drivers reported having back pain in the last year. That is roughly 3 out of every 4 drivers.
It's Not Just the Back: It's not just a single broken part; it's a system-wide issue. The study found that two-thirds of the drivers had pain in three or more different places at the same time (like the back, shoulders, neck, and knees all complaining at once).
The Scale of the Problem: In the general Indian population, about 15–25% of people have back pain. For these bus drivers, that number is three to four times higher. It's like if a normal neighborhood had 10 potholes, but this specific road had 40.

2. The "Sleepy Driver" Connection

The study also checked how tired these drivers were during the day using a test called the "Epworth Sleepiness Scale." Think of this as a "drowsiness meter."

The Link: The researchers found a clear connection: the more body parts a driver hurt, the sleepier they were during the day. It's like a chain reaction: Pain $\rightarrow$ Bad Sleep $\rightarrow$ Daytime Sleepiness.
The Numbers: Nearly 48% of the drivers were in the "excessively sleepy" category. That means almost half of them are fighting to stay awake while driving heavy vehicles.
The Cause: The study suggests that the pain keeps them from sleeping well at night, which makes them sleepy the next day. It's a vicious cycle.

3. Why is this happening? (The Culprits)

The researchers played detective to find out what makes the pain worse. They looked at many factors, like the brand of the bus, the route taken, and the driver's age.

The Real Villain: Lack of Sleep: The strongest factor they found was how much sleep the driver got at night. Drivers who slept fewer hours were much more likely to have back pain. It's like trying to run a marathon on a broken leg; if you don't rest, the injury gets worse.
The Weight Factor: They also found that drivers with a higher Body Mass Index (BMI) tended to have more severe pain, though not necessarily a higher chance of getting the pain in the first place.
The Bus Brand Doesn't Matter: Interestingly, it didn't matter if they drove a "Tata" bus or an "Ashok Leyland" bus. The pain levels were the same. This suggests the problem isn't one specific brand of seat, but rather that all the seats in these buses are designed in a way that doesn't fit the average Indian driver's body.

4. The "Overworked" Reality

The study revealed a hard truth about the rules of the road. There is a law (the Motor Transport Workers Act of 1961) that says drivers should work a maximum of 8 hours a day.

The Reality: 100% of the drivers in this study worked more than 8 hours.
The Extreme: About 14% of them worked more than 12 hours a day.
The Districts: This wasn't just happening in one city; it was happening uniformly across all 14 districts of Kerala. Whether they were in the city or the countryside, the drivers were all working the same long hours and suffering the same aches.

5. What Does This Mean for Safety?

The paper connects these aches and sleepiness directly to road safety.

The Chain Reaction: The study suggests that the physical pain causes poor sleep, which causes daytime sleepiness. A sleepy driver is a dangerous driver.
The Evidence: Previous research in Kerala showed that "ergonomic issues" (like bad seats and long hours) were responsible for about 22% of accidents involving heavy vehicles. This study provides the biological proof: the drivers' bodies are literally breaking down under the strain, which supports the idea that these ergonomic issues are a major cause of accidents.

Summary

In short, this study is like a health check-up for a fleet of bus drivers. It found that they are suffering from widespread body pain (especially in the back), excessive daytime sleepiness, and chronic overwork.

The paper concludes that the solution isn't just telling drivers to "sit up straight." It suggests that fixing the schedule (so they can get enough sleep) and redesigning the seats to fit the drivers' bodies are the most important steps to stop the pain and keep the roads safe. The drivers are essentially running on empty, and the study says it's time to refuel them with rest and better equipment.

Technical Summary: Work-Related Musculoskeletal Disorders among Public Bus Drivers in Kerala

Problem Statement
Professional driving in India, particularly within state-operated transport corporations like the Kerala State Road Transport Corporation (KSRTC), involves high exposure to ergonomic stressors including prolonged static postures, whole-body vibration, and extended duty hours. While previous population-level analyses in Kerala identified ergonomic factors as contributing to 22.1% of heavy-duty vehicle accidents, there was a lack of biological evidence linking these occupational stressors to the physical health of the drivers themselves. Specifically, no comprehensive study had quantified the prevalence and severity of work-related musculoskeletal disorders (WMSDs) across all nine standard body regions while simultaneously assessing daytime sleepiness in a multi-district Indian cohort. Furthermore, the interaction between the "pain-sleep-fatigue" chain and road safety risks remained under-documented in this demographic.

Methodology
This cross-sectional study assessed 405 male KSRTC bus drivers across all 14 administrative districts of Kerala. Recruitment occurred between January 2024 and March 2025. Inclusion criteria required a minimum of two years of driving experience and daily duty hours of at least eight.

Instruments:
- Musculoskeletal Assessment: The Standardised Nordic Musculoskeletal Questionnaire (NMQ) was used to assess lifetime, 12-month, and 7-day prevalence across nine body regions (lumbar, neck, shoulder, knee, hip/thigh, thoracic back, foot/ankle, hand/wrist, elbow).
- Severity: Discomfort severity was quantified using the Body Discomfort Chart (BDC) on the Borg CR-10 scale (0–10).
- Sleepiness: The Epworth Sleepiness Scale (ESS) measured excessive daytime sleepiness.
- Exposure Survey: A structured survey captured demographics, BMI, driving experience, daily duty hours, route type, vehicle brand, and sleep quality.
Statistical Analysis:
- Data were analyzed using R (v4.2.1). Given non-normal distributions for most variables, non-parametric tests (Spearman rank correlation, Kruskal-Wallis) were employed.
- Multiple correlation tests were corrected using the Benjamini-Hochberg false-discovery-rate (FDR) procedure.
- Multivariable binary logistic regression was used to identify predictors for lumbar 12-month prevalence, while linear regression assessed predictors for lumbar severity.
- Exploratory factor analysis (using parallel analysis) was conducted on the nine BDC scores to determine the underlying dimensionality of musculoskeletal discomfort.

Key Results

Prevalence and Burden:
- Lumbar Region: The lumbar back showed the highest burden, with a lifetime prevalence of 88.1%, a 12-month prevalence of 71.9% (95% CI 67.3–76.0), and 16.8% reporting acute symptoms in the past 7 days. This 12-month prevalence is approximately three to four times higher than published rates for the general Indian adult population.
- Multi-Region Comorbidity: The mean number of concurrent affected regions was 3.39. 66.4% of drivers reported disorders in three or more regions. The most common co-occurrence pairs involved the lumbar region combined with the shoulder (38.0%), knee (36.0%), and neck (35.3%).
- Clinical Impact: Lumbar disorders generated the highest healthcare and work-loss burden, with 16.3% of drivers reporting sick leave and 36.5% using medication for lumbar pain.
Daytime Sleepiness:
- The mean Epworth Sleepiness Scale (ESS) score was 10.64 (SD 4.47). 48.4% of drivers fell into the mild, moderate, or severe excessive sleepiness categories.
- Correlations: After FDR correction, ESS scores showed significant positive associations with discomfort severity in seven of nine body regions. The strongest correlations were observed in the shoulder ( $r=0.268$ ), neck ( $r=0.240$ ), and lumbar back ( $r=0.192$ ).
- Stratification: ESS scores increased monotonically with driving experience, daily duty hours, and poor sleep quality. Sleep quality showed the largest effect size ( $\eta^2 = 0.2045$ ).
Risk Factors (Regression Analysis):
- Lumbar Prevalence: Shorter nightly sleep was the strongest adjusted predictor of 12-month lumbar prevalence (adjusted Odds Ratio [aOR] 0.649 per hour; $p=0.021$ ).
- Lumbar Severity: Body Mass Index (BMI) was a significant positive predictor of lumbar severity ( $\beta=0.143$ ; $p=0.008$ ).
- Duty Hours: 100% of the sample exceeded the statutory 8-hour daily duty limit, and 14.3% exceeded 12 hours. No significant difference in lumbar prevalence was found between Tata and Ashok Leyland vehicle brands, suggesting a systemic issue with Indian heavy-duty cabin specifications rather than brand-specific defects.
Factor Structure:
- Parallel analysis supported a single general musculoskeletal-discomfort dimension explaining 24.8% of the variance, indicating that the co-occurring pain in different body regions reflects a shared occupational ergonomic exposure rather than independent pathologies.

Significance and Claims
The paper claims to provide the first comprehensive nine-region NMQ assessment paired with validated daytime sleepiness measurement for an Indian state-operated bus driver population. Its primary contributions include:

Biological Corroboration: The study provides biological evidence supporting earlier findings that ergonomic factors contribute significantly to accident causation in Kerala. The documented musculoskeletal burden (71.9% lumbar prevalence) offers a physiological basis for the "pain-sleep-fatigue" chain that elevates road safety risks.
Occupational Health Baseline: It establishes a baseline showing that the driver population suffers from a systemic, multi-region burden of pain and excessive sleepiness, with nearly half the sample exhibiting excessive daytime sleepiness.
Policy Implications: The findings suggest that interventions should target industry-wide cabin ergonomics and schedule regulation rather than brand-specific redesigns. The strong association between sleep duration and lumbar disorders highlights sleep quantity as a modifiable behavioral target for occupational health programs.
Systemic Nature of Risk: The uniformity of prevalence across districts and vehicle brands indicates that the risk is inherent to the driving task and the standard Indian heavy-duty vehicle design, necessitating structural changes in duty-hour regulation and cabin design to mitigate health and safety risks.

The authors conclude that while the study is cross-sectional and relies on self-reported data, the magnitude of the findings provides a quantitative foundation for future longitudinal research and ergonomic interventions aimed at improving both driver health and road safety in India.