Musculoskeletal disorders associated with obesity: a biomechanical perspective

Despite the multifactorial nature of musculoskeletal disease, obesity consistently emerges as a key and potentially modifiable risk factor in the onset and progression of musculoskeletal conditions of the hip, knee, ankle, foot and shoulder. To date, the majority of research has focused on the impact of obesity on bone and joint disorders, such as the risk of fracture and osteoarthritis. However, emerging evidence indicates that obesity may also have a profound effect on soft-tissue structures, such as tendon, fascia and cartilage. Although the mechanism remains unclear, the functional and structural limitations imposed by the additional loading of the locomotor system in obesity have been almost universally accepted to produce aberrant mechanics during locomotor tasks, thereby unduly raising stress within connective-tissue structures and the potential for musculoskeletal injury. While such mechanical theories abound, there is surprisingly little scientific evidence directly linking musculoskeletal injury to altered biomechanics in the obese. For the most part, even the biomechanical effects of obesity on the locomotor system remain unknown. Given the global increase in obesity and the rapid rise in musculoskeletal disorders, there is a need to determine the physical consequences of continued repetitive loading of major structures of the locomotor system in the obese and to establish how obesity may interact with other factors to potentially increase the risk of musculoskeletal disease.     

The impact of childhood obesity on musculoskeletal form

Despite the greater prevalence of musculoskeletal disorders in obese adults, the consequences of childhood obesity on the development and function of the musculoskeletal system have received comparatively little attention within the literature. Of the limited number of studies performed to date, the majority have focused on the impact of childhood obesity on skeletal structure and alignment, and to a lesser extent its influence on clinical tests of motor performance including muscular strength, balance and locomotion. Although collectively these studies imply that the functional and structural limitations imposed by obesity may result in aberrant lower limb mechanics and the potential for musculoskeletal injury, empirical verification is currently lacking. The delineation of the effects of childhood obesity on musculoskeletal structure in terms of mass, adiposity, anthropometry, metabolic effects and physical inactivity, or their combination, has not been established. More specifically, there is a lack of research regarding the effect of childhood obesity on the properties of connective tissue structures, such as tendons and ligaments. Given the global increase in childhood obesity, there is a need to ascertain the consequences of persistent obesity on musculoskeletal structure and function. A better understanding of the implications of childhood obesity on the development and function of the musculoskeletal system would assist in the provision of more meaningful support in the prevention, treatment and management of the musculoskeletal consequences of the condition.     

The biomechanics of adiposity – structural and functional limitations of obesity and implications for movement

Obesity is a significant health problem and the incidence of the condition is increasing at an alarming rate worldwide. Despite significant advances in the knowledge and understanding of the multifactorial nature of the condition, many questions regarding the specific consequences of the disease remain unanswered. For example, there is a dearth of information pertaining to the structural and functional limitations imposed by overweight and obesity. A limited number of studies to date have considered plantar pressures under the feet of obese vs. non‐obese, the influence of foot structure on performance, gait characteristics of obese children and adults, and relationships between obesity and osteoarthritis. A better appreciation of the implications of increased levels of body weight and/or body fat on movement capabilities of the obese would provide an enhanced opportunity to offer more meaningful support in the prevention, treatment and management of the condition.     

Quality of life and obesity

Interest in the quality of life of patients with different diseases continues to grow. Recent years have witnessed a dramatic rise in the prevalence of obesity worldwide, stimulating interest in the health and quality of life consequences of this phenomenon. The body of research on the quality of life of obese individuals has grown to a point that a review of this literature is warranted. Numerous studies have demonstrated that obese persons experience significant impairments in quality of life as a result of their obesity, with greater impairments associated with greater degrees of obesity. Weight loss has been shown to improve quality of life in obese persons undergoing a variety of treatments. Further research is needed to clarify whether quality of life differs among subsets of obese persons. Until recently, there has been little standardization of quality of life measures in obesity. The SF‐36 has been used in a number of studies of obese persons. Several obesity‐specific instruments have also been developed and have shown great promise. The quality of life of obese individuals is an important issue that should be included in weight management treatment and research.     

Obesity, Depression, and Employment Related Outcomes Among Workers Near Retirement

Obese individuals with comorbid depression face greater risks of atrophied health status alongside the associated adverse consequences, such as limitations of daily living and/or work related activities. This study uses the U.S. Health and Retirement Study database to investigate the likelihood of early retirement decisions (before age 62) of older working-age adults (ages 50 to 62). We find that obese subjects with comorbid depression are significantly more likely to reduce work-hours and seek early retirement. Survival models confirm the negative association between obesity with comorbid depression and the duration to early retirement. The bidirectional association between obesity and depression suggest that more carefully designed public policy interventions are necessary for improving the labor market attachments of the older working-age adults that are obese and clinically depressed.     

The relationship between body weight, frailty, and the disablement process

Objectives. To prospectively examine the relationship between body weight, frailty, and the disablement process. Method. Longitudinal data from the Health and Retirement Study (1998-2006) were used to examine the relationship between being underweight, overweight, or obese (compared with normal weight) and the onset and progression of functional limitations and disabilities in instrumental activities of daily living (IADL) and activities of daily living (ADL) among a nationally representative sample of community-dwelling older adults (aged 50 and older) with characteristics of frailty (n = 11,491). Nonlinear multilevel models additionally adjusted for demographic characteristics and intra-individual changes in body weight, socioeconomic status, health behaviors, and health conditions over the course of 8 years. RESULTS: Compared with their nonfrail normal weight counterparts, prefrail obese respondents have a 16% (p ≤ 0.001) reduction in the expected functional limitations rate and frail overweight and obese respondents have a 10% (p ≤ 0.01) and 36% (p ≤ 0.001) reduction in the expected functional limitations rate, respectively. In addition, frail obese respondents have a 27% (p ≤ 0.05) reduction in the expected ADL disability rate. Discussion. This study's findings suggest that underweight, overweight, and obese status differentially affect the risk for functional limitations and disabilities in IADL and ADL. Among prefrail and frail adults, some excess body weight in later life may be beneficial, reducing the rate of functional limitations and disability.     

Optimizing respiratory function assessments to elucidate the impact of obesity on respiratory health

There is an increasing prevalence of obesity worldwide and its impact on respiratory health is of significant concern. Obesity affects the respiratory system by several mechanisms, including by direct mechanical changes due to fat deposition in the chest wall, abdomen and upper airway, as well as via systemic inflammation. The increased mechanical load in obese individuals leads to reduced chest wall and lung compliance and increased work of breathing. While there is generally minimal effect on spirometric values, as body mass index increases, the expiratory reserve volume, and hence functional residual capacity, reduces, often approaching residual volume in more severe obesity. The majority of evidence however suggests that obese individuals free from lung disease have relatively normal gas exchange. The link between asthma and obesity, while initially unclear, is now recognized as being a distinct asthma phenotype. While studies investigating objective markers of asthma have shown that there is no association between obesity and airway hyper‐responsiveness, a recent working group identified obesity as a major risk factor for the development of asthma in all demographic groups. Although the temptation may be to attribute obesity as the cause of dyspnoea in symptomatic obese patients, accurate respiratory assessment of these individuals is necessary. Lung function tests can confirm that any altered physiology are the known respiratory consequences of obesity. However, given that obesity causes minimal changes in lung function, significant abnormalities warrant further investigation. An important consideration is the knowledge that many of the respiratory physiology consequences of obesity are reversible by weight loss.     

Influence of weight loss on pain, perceived disability and observed functional limitations in obese women

OBJECTIVES: To evaluate the effects of weight reduction by dieting on musculoskeletal pain, perceived disability and observed functional limitations in everyday life. SUBJECTS:: Female outpatients in weight-loss programmes at the Karolinska Hospital, who met the criteria for participating in this study: age 20-65 y and body mass index (BMI) > or =30 kg/m(2). In all, 57 entered the programme studied and 43 completed it. INTERVENTIONS: Diet programmes for 8-12 weeks and thereafter 6688 kJ/day for >52 weeks. MAIN OUTCOME MEASURES: Questionnaires on musculoskeletal symptoms and obesity-specific questions on basic activities of daily living (ADL), mobility, housework, occupational disability and activities outside home. Test protocol developed for observation of functional limitations in obese women. Assessments at baseline, after 12 and after 64 weeks of dieting. RESULTS: In all, 75% completed the study. Weight loss was 14% (14.7+/-6.1 kg) at 12 weeks and, due to a weight relapse, 10% (10.1+/-8.1 kg) at 64 weeks. At the end of the study period, the proportion of current pain from lower backs and feet had normalised. Important perceived improvements were ability to rise from having fallen over, to walk up stairs and to lift heavy things. Most functional limitations improved, such as climbing onto high stools, walking up stairs with grocery bags, doing pedicure, rising from floor or low furniture. The questionnaire results partly followed the weight development, but the observed improvements were long-lasting. CONCLUSIONS: Weight reduction had positive short-term effects on musculoskeletal pain, perceived disability and observed functional limitations. A partial weight relapse had some impact on perceived pain and disability, but not on observed limitations. The maintained improvements may be due to weight loss, but also less pain and increased physical activity.     

Increasing body weight and risk of limitations in activities of daily living: a systematic review and meta-analysis

This study examined the relationship between normal weight, overweight and obesity class I and II+, and the risk of disability, which is defined as impairment in activities of daily living (ADL). Systematic searching of the literature identified eight cross-sectional studies and four longitudinal studies that were comparable for meta-analysis. An additional four cross-sectional studies and one longitudinal study were included for qualitative review. Results from the meta-analysis of cross-sectional studies revealed a graded increase in the risk of ADL limitations from overweight (1.04, 95% confidence interval [CI] 1.00-1.08), class I obesity (1.16, 95% CI 1.11-1.21) and class II+ obesity (1.76, 95% CI 1.28-2.41), relative to normal weight. Meta-analyses of longitudinal studies revealed a similar graded relationship; however, the magnitude of this relationship was slightly greater for all body mass index categories. Qualitative analysis of studies that met the inclusion criteria but were not compatible for meta-analysis supported the pooled results. No studies identified met all of the pre-defined quality criteria, and subgroup analysis was inhibited due to insufficient comparable studies. We conclude that increasing body weight increases the risk of disability in a graded manner, but also emphasize the need for additional studies using contemporary longitudinal cohorts with large numbers of obese class III individuals, a range of ages and with measured height and weight, and incident ADL questions.     

Functional status assessment

Methodology of functional status assessment for musculoskeletal disorders has developed considerably in recent years. Reliability and sensitivity of measurements of physical functions are studied more systematically, and observer tests of activities of daily living functions have been developed with increased accuracy. A major area of interest, however, is reflected in studies of multidimensional assessments of functional limitations and the development of arthritis-specific questionnaires. The importance and difficulties of assessing function in clinical practice have been emphasized. Increasing interest among health planners and health economists in outcome measurements utilizing multidimensional functional assessments is evolving.     

Obesity's effects on the onset of functional impairment among older adults

PURPOSE: This study has two purposes. First, it determines if there is a relationship between body weight and the onset of functional impairment across time among this sample of older adults. More specifically, it examines if obese older adults are more likely to experience the onset of functional impairment. Second, it explores how health behaviors and health conditions may explain the relationship between body weight and the onset of functional impairment. DESIGN AND METHODS: With the use of longitudinal data from the Asset and Health Dynamics Among the Oldest Old (AHEAD) survey, logistic regression models on the onset of functional impairment over two time points are estimated for older adults. RESULTS: Results indicate that body weight (more specifically being overweight or obese) makes one more likely to experience the onset of functional impairment across various domains of impairment. Outside of health behaviors and health conditions, obesity has an independent effect on the onset of impairment in strength, lower body mobility, and activities of daily living. IMPLICATIONS: Study findings support the active treatment of weight problems in older adults. Future directions for research in this area should address effective weight management interventions targeting issues related to older individuals.     

Postheparin plasma lipase activities in obesity: failure to increase with adipose organ enlargement

Published studies have shown that overproduction of very low density lipoproteins is a major factor leading to hypertiglyceridemia in obesity. Few systematic studies of triglyceride removal or postheparin lipoprotein lipase activity (LPLA) in obesity have appeared. We have examined heparin-released lipoprotein triglyceride hydrolase activities in 12 lean and 12 obese age- and sex-matched volunteers after overnight fasting. Heparin doses were calculated to compensate for the disproportionality between body mass and plasma volume in obesity. Triglyceride hydrolase activities of hepatic (HTGLA) and extrahepatic (LPLA) origin were distinguished by in vitro inhibition of LPLA with protamine sulfate. Incremental heparin doses were given to each subject to determine lipase activities under conditions of maximal release and to define sensitivity to heparin-facilitated lipase release. Maximal postheparin LPLA and HTGLA (u/ml plasma or u/total plasma vol) were similar in lean and obese individuals despite a nearly three-fold increase in calculated adipose tissue mass in the obese. Since adipose tissue LPLA has been reported to increase in proportion to adipocyte size, the lack of difference in maximal postheparin LPLA was expected. There was an inverse correlation between plasma triglyceride concentration and LPLA/kg adipose tissue. These empirical observations may reflect relatively decreased heparin-releaseable (functional) LPLA in relation to adipose organ mass in obese subjects. The mechanism of this relationship has not been established.     

Functional limitations linked to high body mass index, age and current pain in obese women.

OBJECTIVE: To describe functional limitations in obese women. DESIGN: Comparisons of functional limitations in obese women and in a normal-weight reference group regarding mobility, balance and housework transport. SETTING: A large room with a corridor and staircase nearby. SUBJECTS: Fifty-seven consecutively selected obese female outpatients, mean age 44 y, body mass index (BMI) 37 kg.m(-2), and 22 voluntary references, mean age 49 y, BMI 22 kg.m(-2). MAIN OUTCOME MEASURES: Pain questionnaire (for background data); a new valid and reliable test protocol measuring activities of daily life (ADL), pain and exertion, heart rate, balance and speed. RESULTS: The patients had problems in performing 13 of 16 actions compared with the references (P-values between 0.05 and 0.001). They moved more slowly and had difficulties and /or pain and exertion in flexibility tasks, balancing, activities at floor level (bending and kneeling), climbing stairs and carrying groceries. BMI (P=0.002), age (P=0.02) and current pain (P=0.02) from the lower body predicted functional limitation. CONCLUSIONS: The functional test reflected functional limitations in obese women, revealing difficulties and perceived pain in ADL. The test protocol can be used to evaluate the effects of training or dieting. For clinical use we recommend considering BMI, age and current pain for use when individualizing advice on training.     

The impairment in daily life of obese haemophiliacs

Summary. Obesity is a major health concern not only in the general population but also in patients with haemophilia. Little is known about the consequences of obesity for haemophilia patients. As obesity is an important risk factor for osteoarthritis, these effects may be even more pronounced in haemophilia patients who are prone to joint damage. The association between obesity and limitations in daily activities as well as the frequency of bleeds and use of factor VIII (FVIII) concentrate in obese and normal weight haemophilia patients was assessed. Fifteen obese (BMI ≥ 30 kg m^?2) and fifteen normal weight (BMI ≤ 25 kg m^?2) haemophilia A patients matched for severity and age were analysed. The Hemophilia Activities List (HAL) was used to assess the impairment in daily activities. Compared with the normal weight haemophilia patients, obese haemophiliacs had a significantly lower sum score (88/100 and 98/100, respectively, P = 0.02), which was mainly caused by an impaired lower limb function. All other components of the HAL also showed lower scores in the obese patients, but did not reach statistical significance. A higher frequency of bleeds requiring treatment with FVIII concentrate occurred in the obese haemophiliacs (17 bleeds in eight individuals) compared with the controls (three bleeds in three individuals) (P = 0.045). Compared with non‐obese haemophilia patients, obese haemophiliacs had more joint bleeds and a lower overall HAL score, which was driven by a lower limb function score. Prevention of overweight and weight reduction requires special attention from physicians treating haemophilia patients.     

Is obesity associated with lower body temperatures? Core temperature: a forgotten variable in energy balance

The global increase in obesity, along with the associated adverse health consequences, has heightened interest in the fundamental causes of excessive weight gain. Attributing obesity to “gluttony and sloth”, blaming the obese for overeating and limiting physical activity, oversimplifies a complex problem, since substantial differences in metabolic efficiency between lean and obese have been decisively demonstrated. The underlying physiological basis for these differences have remained poorly understood. The energetic requirements of homeothermy, the maintenance of a constant core temperature in the face of widely divergent external temperatures, accounts for a major portion of daily energy expenditure. Changes in body temperature are associated with significant changes in metabolic rate. These facts raise the interesting possibility that differences in core temperature may play a role in the pathophysiology of obesity. This review explores the hypothesis that lower body temperatures contribute to the enhanced metabolic efficiency of the obese state.     

The obesity paradox: fact or fiction?

Although the adverse health consequences of obesity in the general population have been well documented, recent evidence suggests that obesity is associated with better outcomes in patients with heart failure (HF). Studies of patients with HF that specifically examined the impact of body mass index (BMI) on outcomes have suggested the existence of an "obesity paradox." However, closer examination of these studies raises important questions on the validity of the paradox. First, the diagnosis of HF in obese patients, particularly when made using clinical variables, may not be accurate; the obese patients in these studies may actually be "healthier" than their nonobese comparators. Second, the deleterious effects of cachexia, rather than the salutary ones of obesity, are likely the main reason for the inverse correlation between BMI and HF outcome, especially once the underlying biologic mechanisms behind cachexia and obesity in patients with HF are considered. Furthermore, few studies have specifically examined the more severely obese population (BMI >35 kg/m(2)) when assessing outcomes, and those that have suggest that severely obese patients may have worse outcomes than patients with normal weights or those who are mildly obese. Therefore, a "U-shaped" outcome curve according to BMI for patients with HF may actually exist, in which mortality is greatest in cachectic patients; lower in normal, overweight, and mildly obese patients; but higher again in more severely obese patients. Further prospective studies assessing the impact of more marked degrees of obesity on outcomes in patients with HF are needed to more conclusively determine whether the obesity paradox truly exists.     

Identification and functional characterization of three novel human melanocortin-4 receptor gene variants in an obese Chinese population

OBJECTIVE: Mutations in the melanocortin-4 receptor gene (MC4R) are the most common monogenic form of human obesity. However, the contribution of MC4R mutations to obesity in Chinese has not been investigated. We studied the frequency of MC4R mutations in an obese southern Chinese population and the functional consequences of the novel variants identified. METHODS: We screened for MC4R mutations in 227 obese [body mass index (BMI) 35.29 +/- 5.75 kg/m2] and 100 lean (BMI 21.57 +/- 0.29 kg/m2) southern Chinese subjects using PCR-direct sequencing. In vitro functional studies, including cell surface expression, ligand binding, and cyclic adenosine monophosphate (cAMP) accumulation, were performed to examine the functional properties of three novel missense mutations. RESULTS: Apart from two previously reported polymorphisms, V103I and -176 A > C, three novel missense heterozygous variants (Y35C, C40R and M218T) were identified. The polymorphisms -176 A > C and Y35C were detected in both obese and normal subjects with similar frequency. C40R was identified only in an obese subject. Pedigree analysis revealed M218T carriers in both lean and obese subjects. The prevalence of V103I carriers in normal-weight controls was significantly higher than that in obese subjects (5.3%vs. 1.3%, P < 0.05). In vitro functional studies showed that all three novel missense variants have normal functions. CONCLUSIONS: Two known polymorphisms and three novel variants of the MC4R were identified. No overt functional defects were observed for the three novel MC4R variants, suggesting that they might not be the cause of obesity in variant carriers.     

The impact of obesity on skeletal muscle strength and structure through adolescence to old age

Obesity is associated with functional limitations in muscle performance and increased likelihood of developing a functional disability such as mobility, strength, postural and dynamic balance limitations. The consensus is that obese individuals, regardless of age, have a greater absolute maximum muscle strength compared to non-obese persons, suggesting that increased adiposity acts as a chronic overload stimulus on the antigravity muscles (e.g., quadriceps and calf), thus increasing muscle size and strength. However, when maximum muscular strength is normalised to body mass, obese individuals appear weaker. This relative weakness may be caused by reduced mobility, neural adaptations and changes in muscle morphology. Discrepancies in the literature remain for maximal strength normalised to muscle mass (muscle quality) and can potentially be explained through accounting for the measurement protocol contributing to muscle strength capacity that need to be explored in more depth such as antagonist muscle co-activation, muscle architecture, a criterion valid measurement of muscle size and an accurate measurement of physical activity levels. Current evidence demonstrating the effect of obesity on muscle quality is limited. These factors not being recorded in some of the existing literature suggest a potential underestimation of muscle force either in terms of absolute force production or relative to muscle mass; thus the true effect of obesity upon skeletal muscle size, structure and function, including any interactions with ageing effects, remains to be elucidated.     

Differences in functional status of Hispanic versus non-Hispanic White elders: data from the Medical Expenditure Panel Survey

OBJECTIVES. Few national studies have focused specifically on the functional status of Hispanic elders. We examined the prevalence of functional limitations and disabilities among Hispanic and Black elders compared to non-Hispanic Whites. METHODS. We analyzed seven measures of functional limitations, disabilities, and dependencies. Logistic regression was used to examine racial and ethnic group differences adjusting for age, gender, and education. RESULTS. Compared to non-Hispanic Whites, Hispanics tended to report greater instrumental activities of daily living (IADL) dependencies and cognitive disabilities. Blacks were more likely to have activities of daily living (ADL) and IADL dependencies and require use of assistive devices compared to non-Hispanic Whites. Further adjustment for respondent status reduced differences between groups, but these models may overadjust for functional status differences. DISCUSSION. Given the projected growth of minority elders, policymakers and planners will need to consider race and ethnic differentials in functional status in determining future medical and social service needs.