A Tale of Two Sexes
Men and women are not created equal — women have a higher risk of some musculoskeletal disorders (MSDs) than men. That was the message that Dr. Julie Côté, associate professor and chair of the Department of Kinesiology and Physical Education at McGill University in Montreal, delivered during a keynote speech at the 9th International Scientific Conference on the Prevention of Work-Related Musculoskeletal Disorders, held in Toronto on June 23.
Even when both genders engage in the same tasks, women report pain, discomfort and other MSD symptoms in the neck and upper limbs twice as often as men do, whereas men are more likely to experience lower-back injuries.
“Sex and gender are complicated,” says Dr. Côté, who defines sex as the biological state that determines whether one is male or female, while gender refers to socially constructed roles, behaviour and activities that a given society considers appropriate for men and women. “Sex and gender have their own operational definitions, but there is significant interaction between them, with aspects of biology influencing psychosocial roles and attitudes and vice-versa,” she says. “That is why we have come to use the expression ‘sex/gender differences’ — to recognize the integration of these influences.”
Sex and gender differences go beyond physical strength to include differences in the types of muscle fibre. Women have a higher proportion of Type 1 muscle fibres, which give them higher endurance, but can also result in women performing tasks for longer durations. The repetitive and invariable nature of tasks that women are more likely to perform, coupled with the fact that they compensate for their weaker strength by engaging muscles at levels close to maximum capacity, could be reasons for the heightened risk of muscle overload and injury among women, Dr. Côté explains.
Marnie Downey, a Canadian certified professional ergonomist and president of ERGO Incorporated in Innisfil, Ontario, thinks that gender plays a role in workplace MSD risk because of physiological and biomechanical differences between males and females. She cites standards like lifting guidelines and safe-material-handling tables, which use data for both males and females. “We do consider gender differences, but we use it kind of as a way to say we want to accommodate as many people as possible,” Downey says.
Shona Anderson, a Canadian certified professional ergonomist and president of Anderson Ergonomics Consulting Inc. in Calgary, agrees. For example, the size of a tool may not fit a woman’s hand as well as it would a man’s, while the grip strength required of a female worker to wield a tool may be greater, thereby hiking the risk of sprains and strains. The height of a production line can also affect male and female workers differently. “Those kinds of things can definitely impact workplace MSDs,” Anderson says.
Differences in how men and women move is another factor behind the higher rates of neck and shoulder injury among women, who tend to have lower motor variability, while men make more minute adjustments when repeating a motion than women do. “Low variability has been shown to be a predictor of injury development,” Dr. Côté adds.
Other gender differences include how men and women respond to fatigue, perceive pain, adapt to physiological stress and hold different job assignments and social roles outside of work. All these factors comprise a model that Côté has developed to guide her research into why neck and shoulder MSDs are more prevalent among women.
“The question we need to ask may not be, ‘Are men and women different?’ but ‘How much so?’” Dr. Côté notes. “This question is all the more pertinent when considering making workplace adaptations to prevent work-related MSDs.”
Mars versus Venus
Studies dating back to the late ‘90s have explored the complex interactions between gender and MSD exposure. Karen Messing, Ph.D., professor of ergonomics at the University of Quebec in Montreal, is the co-author of a 2009 paper comparing two strategies analyzing a single dataset for the relationships between risk factors and MSDs in a population-based sample with a wide range of exposures.
The 1998 Québec Health and Social Survey, which polled 11,735 respondents in paid work, reported “significant” musculoskeletal pain in 11 body regions during the previous 12 months and a range of personal, physical and psychosocial risk factors. Five studies concerning risk factors for four musculoskeletal outcomes were carried out based on these data. Each study included analyses with multiple logistic regression (MLR) performed separately for women, men and the total study population. The results from these gender-stratified and unstratified analyses were then compared.
In the unstratified MLR models, gender was significantly associated with musculoskeletal pain in the neck and lower extremities, but not with lower-back pain. The gender-stratified MLR models identified significant associations between each specific musculoskeletal outcome and a variety of personal characteristics and physical and psychosocial workplace exposures for each gender. Most of the associations, if present for one gender, were also found in the total population. But several risk factors present for only one gender could be detected only in a stratified analysis, whereas the unstratified analysis added little information.
“Stratifying analyses by gender is necessary if a full range of associations between exposures and MSD is to be detected and understood,” the study concludes.
A 2001 study on upper-extremity MSDs among 49,000 Danish workers yielded similar results: the number of complaints and ratios for reporting MSDs were higher among women than men. A 2009 report from the National Institutes of Health in Bethesda, Maryland also found that women are three times more likely than men to develop carpal tunnel syndrome, which could be attributed to women having smaller carpal tunnels.
The types of jobs assigned to men and women also influences MSD risk. Low-force, repetitive upper-limb work is more often assigned to women. The juggling of work life and family roles as caregivers also means that women are less likely to have time to exercise, which is an effective injury-prevention strategy.
As more women are involved in manual material handling, factoring sex and gender differences into research studies will yield a better understanding of injury mechanism. “For many reasons, it would be a mistake to ignore sex and gender in our research designs,” Dr. Côté argues.
Anderson has observed an encouraging trend: companies are increasingly taking physical differences into account when designing workplaces. “I am seeing a lot more adjustability built into all sorts of things, including corporations buying extra small to large sizes of gloves, different-sized handles of tools, height-adjustable desks,” she notes.
While factoring gender differences into workplace ergonomic solutions entails more costs, Anderson says the prices for adjustability have come down dramatically with ergonomic advances and increasing demand for adjustability. The challenge, rather, is time pressure, which can result in employees taking shortcuts instead of taking the time to use devices that minimize physical exertion and injury risk.
Gender difference is not something that Marnie thinks about upfront. “I always look at trying to make the job safer for everybody.” For workplaces like foundries, which are male-dominated, she points out that employers need to ensure they put in as many ergonomic accommodations as they can without creating undue hardship for themselves. “But at the same time, they do have the right to say if you are not able to do the essential duties of the job, whether you are male or female, then maybe the job is not for you.”
Gender differences is only part of the picture for Anderson, who points to the increasing diversity of the workforce. She cites the differences in physique between an Asian worker and someone from the Nordic region as an example. “The difference in size is dramatic between those two people, so it is not just sex and gender,” Anderson argues. “I think workplaces need to focus on striking a balance between all of the people that work in that organization and having adjustability built in for those people.”
Jean Lian is the editor of OHS Canada.