Associations between personality traits, physical activity level, and muscle strength

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Abstract

Associations among personality as measured by the Five Factor Model, physical activity, and muscle strength were assessed using data from the Baltimore Longitudinal Study of Aging (N = 1220, age: mean = 58, SD = 16). General linear modeling with adjustment for age, sex, race, and body mass index, and bootstrapping for mediation were used. We found neuroticism and most of its facets to negatively correlate with strength. The extraversion domain and its facets of warmth, activity, and positive-emotions were positively correlated with strength, independent of covariates. Mediation analysis results suggest that these associations are partly explained by physical activity level. Findings extend the evidence of an association between personality and physical function to its strength component and indicate health behavior as an important pathway.

Highlights

► Muscle strength was associated with domain- and facet-level neuroticism and extraversion. ► We found physical activity level to partly mediate these relationships. ► Having more ‘risky’ personality traits is associated with an increased likelihood of low strength.

Introduction

Although personality has been consistently linked to physical health outcomes including mobility limitations and disability (Brenes et al., 2005, Brenes et al., 2002, Krueger et al., 2006, Wilson et al., 2006), whether personality traits have an impact early on in the disability process is still unclear. According to the Nagi’s Disablement Model, development of disability is a progressive process in which active pathology leads to impairment, which in turn leads to functional limitations and finally to disability (Nagi, 1965). Impairments, the second step in the pathway refers to abnormalities or loss in body systems such as the musculoskeletal system. In young age, available muscle strength exceeds that required to perform normal activities of daily life. However, later in life, declines in muscle strength – the force generated by muscle contraction – diminish the range of activities individuals can perform (Doherty, 2001, Kallman et al., 1990) including mobility (Ferrucci et al., 1997) and other activities of daily living such as personal care activities (Rantanen, 2003). Moreover, lower extremity muscle strength (i.e. quadriceps) has been associated with other health outcomes such as knee osteoarthritis (Slemenda et al., 1997) and falls, especially among adults with chronic conditions (Durmus et al., 2010) and is a strong predictor of mortality risk in older adults (Newman et al., 2006).

The role that personality may play in the process that leads to mobility disability is best described by the Verbrugge and Jette’s Model of disability, which expands the Nagi’s taxonomy to include risk factors and intra- and extra-individual modifiers (Verbrugge & Jette, 1994). This model suggests that personality can directly contribute to development of mobility disability in two ways. First, it can influence the likelihood of developing chronic or acute illnesses (pathology level), which would then initiate the process that leads to musculoskeletal impairments, mobility limitation and disability. Second, once pathology is present, personality can speed up or slow down the progression from pathology to disability.

Although how personality relates to these processes is still unclear, health behaviors and particularly sedentary behavior are perhaps among the most important mechanisms. Within the Five-Factor Model (FFM) of personality (Digman, 1990), neuroticism, extraversion, and conscientiousness have been reported as reliable correlates of physical activity (Bogg and Roberts, 2004, De Moor et al., 2006, Saklofske et al., 2007), being at least as important as other more extrinsic correlates of physical activity (Rhodes & Smith, 2006).

Individuals characterized by negative emotions such as anxiety (McWilliams & Asmundson, 2001), anger and hostility (Anton and Miller, 2005, Higgins et al., 1991), loneliness (Shankar, McMunn, Banks, & Steptoe, 2011) and hopelessness (Valtonen et al., 2009) may be less likely to engage in physical activities compared to those with lower scores on these traits. Among the extraversion facets, activity (Rhodes et al., 2002, Rhodes et al., 2004) and sensation seeking (De Moor et al., 2006, Jack and Ronan, 1998) received the most support as positive correlates of physical activity. A meta-analysis of conscientiousness and health-related behaviors found that being achievement-oriented and persistent (captured by NEO-PI’s achievement striving facet); organized, efficient, and regimented (captured by NEO-PI’s order and self-discipline facets); and self-controlled (i.e. NEO-PI’s deliberation facet) were the strongest correlates of physical activity among 194 studies analyzed (Bogg & Roberts, 2004). On the other hand, physical inactivity has been shown to strongly predict decline in muscle strength, reduced walking speed, and mobility-related disability (see a review by Buchner, 1997), suggesting that level of physical activity may at least in part explain some of the individual differences in muscle strength and other functional outcomes.

In spite of the evidence for relationships between personality, physical activity, and muscle strength, to our knowledge, only one study reported on the association between personality and muscle strength (Jorm et al., 1993). In that study, Jorm and colleagues investigated correlations between neuroticism and extraversion and muscle strength in a sample of older community-dwelling Australian men and women. Neuroticism but not extraversion was found to negatively correlate to strength in women only. More studies are needed to confirm these associations as well as the importance of the remaining three of the FFM personality traits and muscle strength and to assess the potentially mediating role of physical activity. Moreover, investigation at the facet level would provide insight into what specific components of the five personality traits are important in relation to physical activity and muscle strength.

In the current study, we evaluated cross-sectional associations between the five personality traits along with their six facets, physical activity, and muscle strength in the Baltimore Longitudinal Study of Aging (BLSA). We hypothesized that personality would be associated with muscle strength and that health behavior would mediate this association (i.e. Personality  Health behavior  Muscle strength). More specifically, we expected neuroticism and most of its facets to be associated with lower muscle strength. In contrast, we expected extraversion particularly its facets of activity and excitement seeking; and conscientiousness and most of its facets to be positive correlates.

Although no relationship with physical activity was found for agreeableness in a recent meta-analysis of personality correlates of physical activity (Rhodes & Smith, 2006), based on evidence of a positive association of agreeableness with other healthy behaviors (Terracciano and Costa, 2004, Terracciano et al., 2008), we also expected that highly agreeable individuals would have greater strength than less agreeable individuals. Personas characterized by traits such as altruism, compliance, and modesty may be more likely to engage in positive interpersonal relations, which might be conducive of higher levels of physical activity. Though more studies are needed before openness to experience can be reliably linked to physical activity, at least two studies have found a positive association between the two (Courneya et al., 2002, Rhodes et al., 2003). This along with a few other reports of positive associations with self-perceived health (Goodwin & Engstrom, 2002) and survival (Iwasa et al., 2008) led us to hypothesize that high scorers on openness and particularly high scorers on actions (who prefer novel and various types of activities and therefore might be more likely to engage in physical activities) to also have greater strength.

Section snippets

Participants and procedures

The BLSA is an ongoing longitudinal study of community-dwelling volunteers living primarily in the Baltimore–Washington area, who have been continually recruited starting in 1958. In 1978 women volunteers were systematically added to the previously exclusive male study population. Follow-up times vary depending on participants’ age from every 1 year for the oldest old (80 + years) to every 5 years for younger participants (<60 year). These procedures were slightly modified in 2006 to every 4 years

Results

As hypothesized, personality traits pertaining to the dimensions of neuroticism and extraversion were associated with muscle strength, independent of age, sex, race, and BMI (Table 2). The domain of neuroticism was negatively associated with muscle strength. More specifically, each one standard deviation increase in neuroticism was associated with 0.050 (p < 0.001) lower muscle strength. This association was only slightly reduced by the inclusion of extraversion, openness, agreeableness, and

Discussion

Findings from this study extend the body of evidence suggesting an association between personality traits and physical function to a performance-based assessment of muscle strength. We found neuroticism and extraversion, both at the domain and facet level, to correlate with knee extensor muscle strength, suggesting a potentially important role for these personality traits in the process that leads to disability in old age. Our findings also point to physical activity as a potential mediator of

Acknowledgments

This research was supported entirely by the Intramural Research Program of the NIH, National Institute on Aging. Data for these analyses were obtained from the Baltimore Longitudinal of Aging, a study conducted by the National Institute on Aging. PTC receives royalties from the Revised NEO Personality Inventory. The authors declare no other conflict of interest.

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