Differences in musculoskeletal health due to gender in a rural multiethnic cohort: a Project FRONTIER study

Musculoskeletal health involves muscle strength, bone strength, and joint health. A decrease in bone mass and strength, and an increase in adipose tissue and musculoskeletal discomfort characterize the normal aging process [1] and such changes lead to a decrease in physical activity, reduction in quality of life, loss of independence and development of co-morbidities such as worsening cardiovascular [2] and mental health [3]. National Health Interview Survey 2012 reported that three of the four most common medical conditions in the United States were musculoskeletal conditions, including lower back pain, chronic joint pain, and arthritis [4]. Studies reported higher rate of musculoskeletal health issues in rural areas than the US average [5] and a need for access to care in rural areas [6].

Sex differences in the biology of different organ system and the influence of sex hormones in modulating health and disease are increasingly relevant in clinical and research area, including musculoskeletal health. Gender may be a predictor of chronic musculoskeletal health with females at higher risk than males [4]. For example, de Graaf et al. recently reported there are significant difference in short musculoskeletal function assessment between men and women in the Dutch population [7]. In 2012, nearly 10.7 million women, compared with 7.5 million men, reported limitations in activities of daily living due to musculoskeletal conditions [4]. Other contextual variables (e.g., age, education, income), lifestyle/anthropometric variables (e.g., body mass index, height, physical activity), existing diseases (e.g., diabetes, stroke, chronic obstructive pulmonary diseases), and physical functioning impairment have been shown to contribute to walking speed, an indicator related to the musculoskeletal health, in the older US population [8]. In addition to population characteristics and socio-economic factors, blood chemistry parameters such as blood glucose, glycated hemoglobin (HbA1C), low-density lipoprotein (LDL), very-low-density lipoprotein (VLDL), C-reactive protein (CRP), and uric acid, are also highly associated with musculoskeletal health [9‐13].

A recent cross-sectional study [13] reported that increased physical activity was associated with improvements in some metabolic and inflammatory markers of health [13]. On the other hand, increasing research effort has been focused on the role of insulin resistance in age-related conditions or geriatric syndromes, such as musculoskeletal morbidities. Based on a population-based National Health and Nutrition Examination Survey (NHANES), Kuo et al. [14] reported an inverse association between insulin resistance and habitual gait speed in non-diabetic older men (≥50 years), suggesting insulin resistance is an important indicator of gait function among men. Further, Kalyani et al. [15] reported that elevated fasting glucose level was associated with lower grip strength in older men, but not in women without self-reported diabetes and/or use of diabetes medication. Zhang et al. [8] also reported that poor lower extremity function was associated with pre-diabetes/diabetes in older Chinese. However, little is known the correlations between inflammatory and metabolic markers and musculoskeletal health-related parameters including hand grip strength, musculoskeletal discomfort, and gait disturbance in a rural setting, and the differences of such correlations due to gender difference. Such information would provide a base for future nutritional advice and life style education to manage musculoskeletal health in a rural population. Therefore, the current study investigated the factors affecting musculoskeletal health in terms of hand grip strength, musculoskeletal discomfort, and gait disturbance for different genders. We focused on a rural West Texas multiethnic adult and elderly cohort using data collected through the Project FRONTIER (Facing Rural Obstacles to healthcare Now Through Intervention, Education & Research) to explore the natural course of chronic disease development and its impact on longitudinal cognitive, physical, social, and interpersonal functioning in a multi-ethnic adult sample from rural communities of West Texas [16]. Study participants are followed over time to test for changes in physical, mental, and cognitive health and the factors that may influence those changes, in order to collect information for effective disease management and improvement of the overall health of individuals living in this geographic area and beyond. In summary, the objective of this study was to investigate the factors affecting musculoskeletal health in terms of hand grip strength, musculoskeletal discomfort, and gait disturbance for different genders in a rural West Texas multiethnic adult and elderly cohort.

This is the first cohort study to evaluate associations between population characteristics, socio-economic factors, blood chemistry parameters, and musculoskeletal health (hand grip strength, musculoskeletal discomfort, and gait disturbance) by gender. Our rural West Texas population exhibits unique demographic characteristics compared to general population in terms of higher percentage of Hispanic population, higher obesity rate, higher poverty rate, higher unemployment rate, and higher prevalence of chronic diseases, in agreement with results of published studies [21, 22]. In our cohort, 55.4 % of the males and 58.9 % of the females were Hispanic. Compared to non-Hispanic white and others females, Hispanic females had greater musculoskeletal discomfort after adjusting for demographic and socioeconomic factors. Such findings are consistent with Quiben’s study [7] that older Mexican Americans have poorer functional health (as assessed by walking speed) than European Americans.

Socioeconomic status and education were not associated with dominant hand grip strength, musculoskeletal discomfort, or gait disturbance in our rural multiethnic cohort, regardless of gender. This finding is different from the United States national data that health related quality of life in the elderly, as assessed by overall functional health, is positively associated with household income [23]. This discrepancy may be due to the difference in age that our participants’ mean age was about 60 years old compared to 73 years old for the study of Huguet et al. [23]. Further research addressing the elderly population in other rural areas would be valuable to assess if such disparity exist as a general rule.

The present results show that age was an important non-modifiable risk factor for musculoskeletal health decline (i.e., hand grip strength, musculoskeletal discomfort (females only), and gait disturbance (females only), particularly in females. Hand grip strength is known to be associated with functioning in other muscle groups and activities of daily living, as well as incident disability [24]. By stratifying our study cohort by gender, we found that age was an important negative predictor of hand grip strength in both genders and such findings were consistent with previous studies that hand grip strength was strongly and inversely associated with age.

Age was also a marginally significant risk factor for musculoskeletal discomfort and a significant risk factor for gait disturbance in females. The present result agrees with DePalma et al. [25] in that age was associated with significant increase in chronic low back pain in females. Our findings of a positive correlation between age and gait disturbance is also in agreement with Wilson et al. [26] that gait disorder and rigidity are usually progressive with age. Krasovsky et al. [27] investigated gait stability and inter-limb coordination following a perturbation to the dominant leg during walking at comfortable speed, and found that older male adults had a longer period of initial destabilization, took a longer time to recover center of mass stability and double-support duration, and had larger whole body long-lasting phase shifts, suggesting greater risk of gait disturbance than younger male adults. As expected, the aging population is prone to higher rates of nearly all musculoskeletal conditions than younger population. In large part, these conditions can be attributed to wear and tear of bones and joints over a lifetime [4].

Our study suggests that waist circumference was positively correlated with musculoskeletal discomfort in males only. The unit for waist circumference measurement was cm, and for every unit increase in waist circumference, there was a 2.5 % increase ([exp (0.0248)-1], Table 3) in musculoskeletal discomfort rating. Waist circumference is a measure of abdominal obesity. The association between obesity and osteoarthritis is well-established, especially for weight-bearing joints [28], because these joints are used more intensely in rural areas, where people have less access to health care, resulting in greater pain and disability [29]. Moreover, a study has shown that a waist circumference is highly associated with dynapenia, age-associated impairment of muscle strength [30]. A higher percentage of physical inactivity was observed in our rural cohort (27 %) than the Texas average (23 %) [31]. On the other hand, the current study revealed that presence of chronic health problems (having at least one of the chronic health problems of diabetes, pulmonary disease, and heart disease) in females was a significant predictor for musculoskeletal discomfort. Women with chronic health problems reported 40 % higher ([exp (0.3377)-1], Table 3) musculoskeletal discomfort ratings. A recent study by Pelaez-Ballesta [32] concluded that older age, being female, disability, and having had physically demanding work were associated with a greater likelihood of having a musculoskeletal pain. Miro et al. [33] also commented that the prevalence of any pain was similar across age groups but higher in females, and among individuals suffering from pain, 94.2 % reported chronic pain (i.e., pain of more than three months’ duration). Furthermore, several studies have suggested that women are also more sensitive to pain [34, 35]. This may explain why women reported greater musculoskeletal discomfort in our study cohort.

The status of general health was an important predictor of musculoskeletal health in our cohort. For example, the present study showed that participants with fair or poor health were associated with inferior musculoskeletal health, i.e., weaker dominant hand grip strength (females only), greater musculoskeletal discomfort, and higher risk of gait disturbance. The findings of the correlation of overall general health and musculoskeletal health are supported by a previous study showing gait disturbance associated with cardiovascular decline and greater mortality [36].

Interestingly, we found that higher CRP concentration was positively associated with risk for gait disturbance in females (1.09 adjusted odds ratio), a result supported by Arts et al. [37] who reported that performance-based physical frailty (encompassing gait speed, hand grip strength, and low physical activity) was associated with higher levels of inflammatory markers (i.e., CRP, interleukin-6). Moreover, a positive association was found between HbA1c level and gait disturbance in females only; i.e., females have a 32 % increase in risk of gait disturbance per 1 % increase in HbA1c level. This result is supported by Arvanitakis et al. [38] who found that diabetes (defined as HbA1c ≥ 7 %) was associated with worsening gait disturbance in the elderly.

There are several limitations to this study. First, musculoskeletal discomfort was self-reported by participants using a cumulative score with one point for each of the following categories: joint pain, back pain, swelling, stiffness, deformity, muscles aches and locked joints. Information regarding individual pain category was dichotomous (yes/no) collected during the medical examination review of systems without any detailed information regarding the degree of pain. This combination was based on a review of the interview items tapping elements of musculoskeletal-related pain and a decision to weight them equally when summing the number of different complaints endorsed by each participant. Authors made it as a logical decision to come up with a summary measure. The same reasoning was used for creating “gait disturbance” defined as the presence of at least one of the gait abnormalities including stiff, spastic, narrow-based, wide-based, unstable and shuffling gaits. The gait determinations were made by physicians as part of the standardized medical exam and possibly being drawn from interview items. Both assessments placed less emphasis on analyzing specific musculoskeletal conditions versus generally abnormal musculoskeletal health. There is no independent validation of this combined measure of musculoskeletal discomfort and gait disturbance. Future studies are warranted to test for replicable results across populations which would then support its validity.

Second, the cross-sectional nature of the present study prohibits any causal conclusion. Third, other factors (e.g., dietary intake and physical activity patterns) may exist between genders accounting for hand grip strength, musculoskeletal discomfort, and gait functioning analyzed in this study. Despite these weaknesses, the current preliminary study paves the way for a more in-depth study of community musculoskeletal health by gender. While the present work was a cross-sectional study focusing on hand grip strength, musculoskeletal discomfort, and gait disturbance, future research should include longitudinal studies with interventions to improve musculoskeletal health targeting weight control and chronic disease prevention by gender in rural populations.

Although population aging is driving the epidemic of chronic diseases worldwide, substantial potential exists to modify the overall health decline associated with aging thereby reducing the burden of disease that arises mainly from disability and long-term care health expenditure [39]. This is of importance as more than one third of our participants reported to be in fair or poor health, and that rural-urban disparities in quality of life persist and less access to care in rural areas may contribute to these disparities [40]. Research outcomes support the value of community-based health promotion programs in rural areas, incorporating multidisciplinary health team and culturally competent materials to help elderly rural inhabitants enjoy better health and quality of life [41]. Such programs could be valuable in rural areas of West Texas, and the results of the present study may contribute to the design of the musculoskeletal health aspect of the program.

Age, report of “arthritis”, fair or poor health and selected biomarkers indicative of systemic inflammation were negatively associated with musculoskeletal health in a rural multiethnic cohort. Males with greater waist circumference had greater musculoskeletal discomfort. In females, fair or poor health, advanced age, chronic health problems, C-reactive protein, and HbA1c was negatively associated with musculoskeletal health, where the association was not seen in males. Improving population overall health and educating on healthy lifestyle in regard to exercise and diet could be investigated for their effect on musculoskeletal health. Further rural and multiethnic prospective studies are warranted.