¹Department of Epidemiology and Global Health, Umeå University, Umeå, Sweden
²Department of Community Medicine and Rehabilitation, Umeå University, Umeå, Sweden
³Department of Public Health and Clinical Medicine, Umeå University, Umeå, Sweden
⁴Section of Biomedical Engineering and Radiation Physics, Department of Diagnostics and Intervention, Umeå University, Umeå, Sweden
⁵IMM Institute of Environmental Medicine, Karolinska Institutet, Umeå, Sweden
⁶Division of Ergonomics, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden

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Introduction: Exposure assessment of wrist velocity and muscular activity in hand-intensive work are pillars in risk assessment of hand-intensive work in workplaces. Workers who are engaged in hand-intensive work, such as assembly and food processing, have an increased risk for musculoskeletal disorders (MSDs) and carpal tunnel syndrome (CTS) diagnosis. Foremost, the MSD and CTS prevalences are notably higher in females. We lack knowledge of whether wrist velocity and muscular activity are the same in women and men in identical tasks. This might lead to over- or underrating of risk in males and females, hence missing out on optimal risk-reducing actions to sufficiently protect women and men. Risk assessment which sufficiently protects both sexes from ill-health, supports a sustainable working life for women and men equally. Therefore, it is essential to investigate if exposure is the same in women and men in identical tasks, in regular work.

Purpose: We aimed to investigate if wrist velocity and muscular activity are the same in females and males in identical hand-intensive tasks.

Methods: Participants comprised 28 female-male pairs (56 individuals) who worked in one of 18 different hand-intensive occupational tasks in their regular workplace. Wrist angular velocity was measured with inertial measurement units placed on the dorsal hand and distal forearm, and characterized by the 50^th percentile (median). Forearm muscular activity was measured in the flexor carpi radialis (FCR) and extensor carpi radialis (ECR) with surface electromyography. This was normalized to the maximal voluntary electrical activation (MVE). The 50th percentile (median) was computed, and also the time spent in muscular recovery (<0.5%MVE). To test between-sex differences, the Wilcoxon signed rank test was used.

Results: Median wrist angular velocities did not significantly differ between sexes (p= 0.374). The muscular activity for FCR and ECR was significantly higher in females than in males, double compared to males (FCR p=0.001, ECR p=0.003). The time spent in muscular recovery was less in females (than in males (FCR p < 0.001, ECR p=0.002), for both FCR (females 0% of the time; males 8.1%) and ECR (0%; 0.2%).

Discussion: Median wrist angular velocities did not significantly differ between sexes (p= 0.374). The muscular activity for FCR and ECR was significantly higher in females than in males, double compared to malest (FCR p=0.001, ECR p=0.003). The time spent in muscular recovery was less in females (than in males (FCR p < 0.001, ECR p=0.002), for both FCR (females 0% of the time; males 8.1%) and ECR (0%; 0.2%).

Conclusion: In regular identical hand-intensive work tasks, females’ muscle activity was higher, and muscular recovery time lower than that of males.

Implication: These findings have a direct impact on risk assessments in hand-intensive work. In jobs where female workers are involved, the risk assessment should be based on females. When using observational risk assessment methods, the risk criteria level should ensure a safe level for women to execute the job with a low risk of acquiring work-related musculoskeletal disorders.