To our knowledge, this is the first study that has specifically examined degree to which the negative impact of chronic conditions on quality of life in older adults could be attributed to a lack of physical activity. The results suggest that physical activity partially mediates the impact of chronic conditions on several health outcomes that are important to quality of life. Physical activity of at least 1,000 Kcal per week was associated with relatively fewer mobility limitations, reduced pain, and greater emotional wellbeing (i.e., happiness). The clinical relevance of the mediating role of physical activity can be inferred by comparing the magnitude of the indirect effect to that of the total effect, which indicated up to 27% mediation for mobility limitation, up to 12% mediation for pain, and up to 16% mediation for emotional wellbeing. These findings concur with those of other studies. For example, adequate physical activity was associated with a significant reduction in the number of days of poor physical and mental health status in adults with arthritis .
The US Center for Disease Control and the American College of Sports Medicine guidelines  recommended that individuals should engage in 30 minutes or more of moderate-intensity physical activity on a daily basis (equivalent to approximately 1,400 Kcal/week) while the US Surgeon General's 1996 report classified moderate physical activity as more than 1,000 Kcal/week . We found a low level of participation in leisure-time physical activity regardless of chronic disease status among older Canadians. Specifically, only 35% of older adults without any chronic condition and 26% of those with one or more chronic conditions met the 1,000 Kcal/week criterion.
Epidemiological data have established that physical inactivity decreases the incidence of at least 17 unhealthy conditions, most of which are chronic conditions or risk factors . Our study further elucidates the importance of physical activity for older adults who have a chronic condition. We found that older adults with chronic conditions who were physical active (i.e., leisure-time physical activity of at least 1,000 Kcal per week) reported better health outcomes related to mobility, pain, and emotional wellbeing than those who were physical inactive. Leisure-time physical activity likely mediates the negative association between chronic conditions and these specific self-reported health outcomes in older adults by: 1) maintaining or augmenting physiological functions (e.g., prevention of sarcopenia); 2) reducing the likelihood of acquiring additional chronic conditions; 3) delaying the progression of current chronic condition(s); and 4) improving mental health and sense of wellbeing. In sum, physical activity beneficially affects the human body in a multifactorial manner.
Regular physical activity not only directly promotes mobility in older adults via mechanisms such as improved muscle strength and postural balance but also indirectly by, for example, reducing the risk for falls and fractures [34, 35]. Maintaining the capacity for independent mobility and living is important to older adults and contributes to their general sense of emotional wellbeing [36, 37]. Physical activity can enhance emotional wellbeing via increases in: 1) beta endorphins; 2) the availability of brain neurotransmitters (e.g. serotonin); and 3) self-efficacy . In addition, physical activity may mediate the negative association between chronic conditions and health outcomes by reducing the likelihood of acquiring additional chronic conditions and delaying the progression of current chronic condition(s). Most prevalent chronic conditions have an association with physical inactivity, and a number of risk factors for chronic conditions are precipitated by physical inactivity (e.g., obesity  and insulin resistance ).
Unfortunately, individuals with chronic conditions are at the highest risk of physical inactivity  – placing these individuals at greater risk for acquiring additional chronic conditions. According to Booth and coworkers , physical inactivity is the key environmental factor contributing to the substantial increase in the incidence of chronic conditions in the latter part of the 20th century. Thus, physical activity can prevent the onset of chronic conditions. Our findings suggest that physical activity could also be beneficial for older adults who already have one or more chronic conditions. These findings provide further support for health promotion programs that facilitate or encourage increased leisure-time physical activity in older people with chronic conditions.
In this study, physical activity is measured as the time spent performing leisure-time activities. Despite the comprehensive nature of this information, daily activities performed by individuals are not represented in these data and therefore physical activity was conservatively estimated. In addition, some respondents may not have been able to accurately recall all their leisure-time physical activities for a period of three months. This may explain why the magnitude of the mediation effect that we observed in this study was smaller than we had anticipated. We specifically expected that the OR for the association between having a chronic condition and physical activity would have been larger. Non-response bias may also have contributed to these results (e.g., older adults with severe physical or mental health problems may have been less likely to complete the survey).
A few other limitations should be noted. Although the relationships were specified to examine the mediating effects of physical activity, the direction of these relationships could also operate in the reverse. The cross-sectional nature of the data does not allow us to confirm claims pertaining to the causality of these relationships. It seems just as likely that poor ambulation will lead to a decrease in physical activity which could lead to a variety of chronic conditions. In addition, the utility weights for the HUI3 may not be generalizable considering that they are based on a community sample of 504 adults in the city of Hamilton, Ontario, Canada . Nevertheless, these weights were only used for calculating the total HUI3 scores; they were not used to measure each of the health attributes which were included as binary variables in our analyses. And, there is a lack of independence in our categories of chronic conditions. For instance individuals who have had a stroke are likely to have cardiovascular conditions as well. Finally, some chronic conditions that may impact quality of life in older adults (e.g., epilepsy and migraine headaches) were not included in our analyses.