In this cohort of post-MI patients, the predictive role of SOC in long-term trajectory of LTPA was evident, even after controlling for sociodemographic and psychological factors and disease severity. Weak SOC was consistently associated with lower engagement in LTPA throughout follow-up. SOC was associated with income, educational level, employment status, self-rated health and depressive symptoms, matching the findings from a healthy population survey [20], and indicating that SOC reflects personal, social and economic resources.
Previous research has investigated the role of SOC in health outcomes and behaviours. The European Prospective Investigation into Cancer (EPIC) study reported a 30% reduction in both all-cause and cardiovascular mortality associated with a strong SOC, independent of age, sex, and prevalent chronic disease [9]. This link suggests that SOC confers a form of resilience against disease, however the explanatory pathway for the SOC-mortality relationship remains unclear. In a follow-up of the EPIC, lifestyle choices including diet, smoking and physical activity, and SES explained 23% of the association between SOC and mortality [10]. Since lifestyle behaviours were measured at a single time point, their true contribution may be even greater. The current study measured physical activity on 5 separate occasions over a 13 year period and found a significant association between SOC at baseline and LTPA trajectory.
Evidence for the link between SOC and health behaviours has been reported in several studies, including in healthy college students [21] and hypertensive patients [22]; SOC has previously been associated with smoking [22, 23] and oral health behaviours [24–26], as well as physical activity [10, 23, 24, 27]. In a British survey of 18,000 adults, participants with the strongest SOC were 28% less likely to be current smokers and 36% less likely to be physically inactive than those with the weakest, independent of sociodemographics [23], although this study was based on a 3-item assessment of SOC rather than the full 29-item questionnaire used in the present study. In a student cohort followed up for 3 years, frequency of physical activity was related to strength of SOC [27]. A prospective study of middle-aged Finnish men found that differences in LTPA depended on SOC [28]. However, these studies were cross-sectional [23, 24], involved small samples [27], or assessed SOC several years after physical activity [28] therefore providing limited evidence of the predictive role of SOC in physical activity.
The relationship between SOC and health behaviours has rarely been examined in MI patients. A small-scale study tackled this issue, and found that post-MI patients who chose to participate in an exercise-based rehabilitation programme had significantly higher SOC scores at baseline than those who declined to take part [29]. Additionally, a discriminant analysis showed that SOC score successfully differentiated attendees from non-attendees. The current study examined the predictive role of SOC in engagement in physical activity in a much larger sample, controlled for a wide range of confounding variables, and had a follow-up of 13 years. We focused on leisure time physical activity since, although cardiac rehabilitation programmes are indispensable in post-MI recovery, long-term maintenance of physical activity is key to secondary prevention.
Our finding that baseline SOC score was significantly associated with LTPA after 10-13 years suggests that a strong SOC may be involved in the maintenance of health behaviours. Figure 1 illustrates that LTPA prevalence increased in all groups after MI, although the increase was steeper in strong SOC patients. The problem encountered, as with all health behaviours, is the gulf between adoption and maintenance, indeed Leung and colleagues found in a cohort of patients with coronary artery disease that while exercise behaviour increased after discharge from hospital, it had decreased after 18 months [30]. It is therefore interesting to note that while many of our post-MI cohort increased their activity level after MI, no doubt in many cases on medical advice, it was the individuals with a weak SOC who had much higher odds of decreasing levels of activity 10-13 years later. It should also be noted that at the last interview (T5), less than 1% of LTPA data were missing, therefore a more accurate picture of activity habits was available compared to earlier timepoints which had 10-15% missing data.
A strong SOC was additionally associated with pre-MI LTPA habits, perhaps indicating that these individuals led a healthier lifestyle to begin with. We may then have expected that high SOC patients would remain consistently ahead of their lower SOC counterparts in the activity stakes. The fact that LTPA not only remained more prevalent, but increased at a higher rate post-MI in the higher compared to lower SOC groups, suggests that SOC may be related both to health behaviours in general, and to secondary prevention behaviours as an adaptive coping mechanism after illness.
Possible mechanisms
The salutogenic model was designed to explain improvement in one's location on the health-disease continuum [7]. Antonovsky hypothesized that individuals with a strong SOC would engage in adaptive health behaviours more often than those with a weak SOC [14]; however he also suggested that strength of SOC has direct physiological consequences affecting health, an early nod to psychoneuroimmunology [31].
A strong SOC has been associated with reduced mortality [9, 10], suggesting that SOC confers a form of resilience against disease. Health behaviours, including physical activity, may be one of the ways in which SOC influences health. SOC level rests on the presence or absence of generalized resistance resources [8]-these may include material and financial resources (eg. money for gym membership or sports equipment), social support (a supportive partner or friend with whom to engage in exercise), flexibility (the ability to make changes to one's daily routine and adapt to change), knowledge and physical health status. Patients with a strong SOC in our cohort possessed many of these resources which may facilitate achievement of health goals. Furthermore, high SOC may improve one's ability to identify available resources [15], improving the chances of choosing an appropriate coping strategy from among these resources.
According to Antonovsky, SOC is as an adaptive dispositional orientation, with the three components of SOC determining how an individual adapts to a stressful situation [14]. Surtees and colleagues further reported that a weak SOC was associated with a slower adaptation to adverse events [32]. Adaptive capacity may then be the most important element of SOC in post-MI patients, since recovery and rehabilitation require lifestyle changes. Perception of the condition as manageable, comprehensible and meaningful allows the individual to perceive the situation as a challenge, and to accurately identify and make use of resources in his environment in order to adapt and overcome this challenge [14]. This may include making significant changes to daily life. On the contrary, perception of the situation as overwhelming, incoherent and exceeding one's resources may reduce adaptive capacity, making lifestyle changes difficult. In the same way that lower SOC individuals were less likely to quit smoking post-MI [11], so they may also find it harder to adopt and maintain physical activity habits, due to reduced resources and lower adaptive capacity.
Finally, it has been suggested that individuals with a strong SOC may more accurately identify the nature of a situation [33]. In the context of illness this may translate to a better comprehension of the influence of behaviour on health outcomes, which could motivate behaviour change.
Methodological considerations
Several limitations of our research should be considered when interpreting the results of this study. Participants were relatively young survivors of MI, therefore results may not be generalizable to older patients. LTPA was self-reported, which may introduce misclassification bias. SOC was measured just once, during initial hospitalization, which may cause a substantial underestimation of the true association between SOC and LTPA after MI. Antonovsky described SOC as a stable trait, "a global orientation that is pervasive and enduring" [8], formed by childhood experiences and reinforced by life experiences. Indeed test-retest correlations show considerable stability, e.g. 0.54 over a 2-year period among retirees [7]. While traumatic events including illness can temporarily modify the SOC, it is expected to return to normal or 'bounce back' [14]; in fact SOC scores in our post-MI cohort were previously reported as being similar to population scores, implying that even the serious event of MI may not significantly alter SOC [34]. However, some research indicates that SOC may vary with time, for example in a cohort of accident victims, SOC decreased following trauma and remained lowered after 12 months [35] and in CABG patients, 41% showed changes in their SOC during a 1 year follow-up [36].
The study benefitted from repeated assessment of LTPA over 13 years and parallel assessment of multiple confounding factors. There are some indications that depression may be associated with post-MI LTPA [37] therefore we took this variable into consideration as a confounding factor.
