Assessing the impact of job demands and hazardous workload activities on musculoskeletal symptoms in stone,sand,and gravel mining operations

2.1 Participants

Cross-sectional survey data were collected from 459 full-time adult workers employed in small to medium-sized stone, sand, and gravel mining organizations in Indiana. Our sample exceeded the suggested minimum sample size of 332 participants, which was based on a projected population of 2400 stone, sand, and gravel mine workers in Indiana, 5% margin of error and 95% confidence interval. Convenience sampling was used to recruit participants completing U.S. Mine Safety and Health Administration (MSHA) annual refresher training at their workplace or at a training facility that conducted MSHA annual refresher training. All participants in the training programs were recruited to voluntarily participate in the survey either prior to their training session or while on a break. Researchers obtained consent from all participants prior to their participation. Two persons declined to participate during the study. No personally identifiable information was collected during this project. The study was ethically conducted and the protocol for the study was approved by the Institutional Review Board at Indiana University on February 22, 2019 (IRB#1902635452).

2.2 Data collection and measures

Data utilized in this study were collected via a survey instrument that adapted items and measures from the Dutch Musculoskeletal Questionnaire (DMQ) [30, 31]. The DMQ is a reliable and valid instrument [31] used extensively in research to assess relationships between workload factors and self-reported musculoskeletal symptoms. Research studies often use the instrument to identify risk factors for musculoskeletal problems. It has been used in research across a wide variety of workers and occupational groups from academicians [32] to veterinary workers [33], including coal miners [20].

Items and measures from the DMQ [30, 31] provide an opportunity to examine the presence or absence of exposures related to workload factors. According to Hildebrandt, questions from the DMQ are categorized into potentially hazardous workloads and working conditions, such as forceful exertions that include lifting, carrying, supporting, pushing, pulling and pinching; dynamic loads, such as walking, bending and twisting of trunk, neck or wrists, stooping, squatting, reaching; static loads, such as sitting, standing, prolonged bent or twisted posture of trunk, neck or wrists, working with hands above shoulder level, kneeling or squatting posture; peak loads that include sudden, forceful movements, unexpected movements; repetitive load; and, ergonomic environmental conditions such as climatic factors, vibration, limited working space and slipping and falling [31].

The outcome, musculoskeletal symptoms, was assessed by asking participants if they experienced any pain or discomfort during the past 12 months at specific body regions. For this study, we specifically focused on low back, neck, shoulders, and wrists as musculoskeletal disorders and symptoms mostly occur at these body parts and regions among stone, sand, and gravel mine workers [6, 9]. Workload measures were assessed by asking participants about their musculoskeletal workload exposure through a series of questions, such as how often they lifted heavy loads, bent, or twisted their neck, torso, wrists/hands, worked in bent or twisted positions for long periods, worked in the same posture for long periods, made frequent repetitive movements, stood, or sat or walked for long periods, often held vibrating tools, etc. For the purposes of this study, questions were grouped under five indices, which are forceful exertion, dynamic loads, static loads, repetitive load, and vibration. The questions and groupings, presented by Hildebrandt and colleagues [30, 31], guided the groupings and our methodology used in the examination of relationships.

The analyses described below, will delineate which workload factors may increase the odds of MSDs and their resultant symptoms among stone, sand, and gravel mine workers. As such, the findings should provide guidance on how work within stone, sand, and gravel mining operations should be designed and organized to protect the health, safety, and wellbeing of workers in this mining sector, to bolster the effectiveness of operations and to curtail costs associated with diminished worker health.

2.3 Analyses

The analyses were modeled after analyses presented by Hildebrandt and colleagues [30, 31]. Data entry, data cleaning and data processing were initially conducted using SPSS v25. Statistical analysis was conducted using STATA MP version 14. Logistic multiple regression models (see Table 2) were examined with musculoskeletal symptoms of the wrist/hand, neck/shoulder, and low back as separate dependent variables. Independent variables included five workload measures including forceful exertions, dynamic load, static load, repetitive load, and vibration [30, 31]. Confounding variables were included in this model to include age, gender, education, average work hours per week, work shift and health status. Additionally, binary logistic regression analyses were completed to further examine associations between specific physical workload demands and wrist/hand musculoskeletal symptoms, neck/shoulder musculoskeletal symptoms and low back musculoskeletal symptoms. For these analyses, participant responses were noted to be “yes” or “no” regarding whether the specific workload demand existed within their job and work tasks. The number of “yes” responses were calculated as the measure for the category. This method is based on analyses completed by Hildebrandt and colleagues [30, 31]. The binary logistic regression analyses delineated associations between workload demands and wrist/hand musculoskeletal symptoms, neck/shoulder musculoskeletal symptoms and low back musculoskeletal symptoms (see Table 3). Odds ratios and 95% Confidence Intervals (CI) were calculated for logistic regression analyses. Significance level was set at.05 level, but p values smaller than.01 were also remarked during the analysis.

4.1 Discussion and implications

This study shows there are significant musculoskeletal symptoms associated with stone, sand, and gravel mining work operations, job demands and workload requirements. Forceful exertions were problematic, particularly pushing or pulling heavy loads. This may be attributed to muscle fatigue during push/pull activities, which has been associated with musculoskeletal disorders [34, 35]. Converting lifting and/or carrying tasks to pushing or pulling tasks has been suggested as a method to control exposures associated with lifting and/or carrying heavy loads [36, 37]. However, the results of the present research indicate this may be problematic within stone, sand, and gravel mining operations, as it has been in other industries [38]. Pushing or pulling heavy loads significantly increased the likelihood of low back, neck/shoulder and wrist/hand musculoskeletal symptoms among stone, sand, and gravel mine workers. Pushing or pulling activities may also increase risks as they can often result in injury incidents, particularly struck-by incidents [38]. Given these outcomes, pushing or pulling may not be a good countermeasure to lifting and/or carrying in stone, sand, and gravel mining operations. These material handling tasks were also problematic, but less so when compared to pushing or pulling. Lifting and carrying increased the likelihood of musculoskeletal symptoms for some of the bodily regions, but not all. Lifting heavy loads increased the likelihood of neck/shoulder musculoskeletal symptoms and wrist/hand musculoskeletal symptoms. Carrying heavy loads was associated with increased odds of wrist/hand musculoskeletalsymptoms.

These results suggest work design changes are needed to address lifting, carrying, and pushing or pulling of heavy loads. Eliminating the tasks would be preferred; however, if this is not possible, machinery, safer technology, equipment and tools or engineering controls are needed to reduce risks. Additionally, administrative controls such as reducing load, reducing distance, reducing number of tasks and the like should be considered to further reduce risks and to protect workers [36, 40].

The present study suggests musculoskeletal workload, including dynamic load and static load are problematic, accounting for symptoms across all three bodily regions examined. The odds of reporting musculoskeletal symptoms are higher for dynamic loads compared to static loads, but both indicate they are associated with the increased likelihood of symptoms. Dynamic loads, particularly bending and twisting of the torso or trunk, bending, and twisting of the neck and bending and twisting of workers’ hands and wrists were problematic, increasing the likelihood of musculoskeletal symptoms at multiple body parts or regions. Extended reaching with the arms and hands also presented a hazardous exposure for workers. The greatest concern seems to be with wrist/hand musculoskeletal symptoms. The likelihood of suffering wrist/hand musculoskeletal symptoms was 11 times higher with tasks that required bending or twisting of wrists/hands. Extended reaching of arms and hands increased the likelihood of wrist/hand musculoskeletal symptoms by more than threetimes.

As noted previously, static load factors were also an identified concern. Two variables that increased the likelihood of low back musculoskeletal symptoms included working in bent, stooped, or twisted posture at the torso or trunk, and working in an uncomfortable posture. The increased likelihood of neck/shoulder musculoskeletal symptoms was associated with working in a bent, stooped, or twisted posture with the neck. Working in an uncomfortable posture also increased the likelihood of neck/shoulder musculoskeletal symptoms. Similarly, wrist/hand musculoskeletal symptoms were associated with work where the wrists/hands were bent or twisted. Additionally, wrist/hand musculoskeletal symptoms were associated with work that required workers to hold their arms at or above shoulder level, work above shoulder level and work below shoulder level.

Repetition is a significant risk factor for musculoskeletal disorders [11, 41]. This is also the case within stone, sand, and gravel mining operations. Repetitive movements of the torso or trunk increased the likelihood of low back musculoskeletal symptoms, repetitive movements with wrist/hands increased the likelihood of wrist/hand musculoskeletal symptoms, and repetitive movements with arms, hands and fingers increased the likelihood of wrist/hand musculoskeletal symptoms. The use of vibrating tools also increased the likelihood of wrist/hand musculoskeletal symptoms, as well as low back musculoskeletal symptoms. This is consistent with the literature across multiple industries and occupations [42].

Overall, the results of the present study are mostly consistent with other industries and occupational groups. Results provide insights into workload hazards and work demands that need to be abated or controlled by mine organizations to reduce risks to acceptable levels and to curtail musculoskeletal disorders and their associated symptoms. This is necessary as preventing injury and promoting health and wellbeing of workers is of utmost importance. Additionally, musculoskeletal-related injuries are costly and result in significant time away from work [8, 28]. Providing a safe and healthy workplace for stone, sand, and gravel mine workers may bolster safety climate and maintain a satisfied and productive workforce [43], which is cost beneficial. This is not only important today, but in the future. The demand for stone, sand, and gravel mine products and materials has grown significantly and is expected to grow in the future [44, 45].

The present study did not study specific job tasks performed by workers, as this was beyond the scope of the project. Taking this into consideration, more targeted ergonomic job task analyses may be warranted. Particularly, maintenance and equipment operators have been identified as possible targets for more directed ergonomic analyses among stone, sand, and gravel mine workers [46]. Various physical methods could be used to identify specific job hazards and risks [47]. Posture evaluation tools such as the Ovako Working Posture Analysis System (OWAS) [48], the Rapid Upper Limb Assessment (RULA) [49] and the Rapid Entire Body Assessment (REBA) [50] could be utilized, along with other tools such as the strain index [51]. These methods or tools could be utilized to delineate risks that should be targeted to reduce the risk of developing musculoskeletal disorders. In general, the findings of the present study suggest more evaluation needs to be completed and controls are needed to protect workers.

4.2 Future research

Continued research within the stone, sand, and gravel mining industry is needed. Research that applies ergonomic assessment and job hazard assessments to the job demands or specific workload requirements identified may help further identify specific steps or processes that could be controlled or abated thereby reducing material handling requirements or abating the hazard completely. Additionally, these controls need to be tested and evaluated. Evaluation research within ergonomics and safety is important to support and justify recommended controls that may protect workers in the future.

The present study, along with prior research by Smith and colleagues [52], which suggests personal health issues also place workers at risk for musculoskeletal symptoms, provide credence that Total Worker Health ® (TWH) approaches to preventing musculoskeletal disorders within stone, sand and gravel mining operations should be examined. TWH provides an effective blend of two disciplines: health protection (safety) and health promotion. This presents an opportunity for interdisciplinary and multidisciplinary research developing, implementing and evaluating initiatives aimed at improving the overall health and wellness of employees as well as curtailing safety and ergonomic hazards.

Lastly, given the high prevalence of musculoskeletal symptoms in stone, sand, and gravel mining operations [6] and the extensive hazards identified in this study, it would be worthwhile to explore whether new technologies, such as exoskeletons, are applicable and effective with reducing exposures and musculoskeletal disorders. Researchers need to examine whether exoskeletons or related technology are usable within the industry and whether employers are willing to adopt such technology at this time.

4.3 Limitations

Although the novel findings are robust, some research limitations should be considered when interpreting the data. Cross-sectional data were collected, which limits causal inferences. There is a potential for biases, including social desirability, since data were collected from participants using survey methods. No personal data were collected, and responses were anonymous, which helps limit the potential for these biases. Outcome data were self-reported. Convenience sampling methods were used. Since mine workers were employed by multiple companies, we were not able to collect records to compare self-reported information to other reports of musculoskeletal symptoms or injuries reported to employers. Lastly, data were collected from mine workers operating in one geographic region of the United States. Although our sample is representative of stone, sand, and gravel mine workers across the United States, we do not fully understand how generalizable our findings are to this mining sector across the United States orinternationally.