In this cohort of Canadian adults reporting high levels of physical activity, we observed relatively low levels of leisure-time activity, compared with occupational and household activity. On average, these latter two domains accounted for more than 80% of overall hours of daily physical activity, the majority of daily activity-related energy expenditure, and accounted for differences in PAL categories among both men and women. Transportation-related physical activity (which could potentially make significant contributions to overall daily activity) was negligible in both men and women.
Among men, occupational activity appeared to be the most influential in determining activity level. The increases observed in time spent in light and moderate-to-vigorous activities within this domain, as levels of activity increased from inactive to active, suggest that all activities that are not sedentary play a role in determining activity level, with perhaps light activity being more important in preventing complete inactivity. Hence, among inactive groups, emphasis on even increasing levels of light activity (between 1.5 and 3 METs) may be helpful . For very active men, less sedentary time and longer durations of moderate-to-vigorous activities were observed compared with men at lower levels of activity, suggesting that displacement of sedentary time may be necessary in order to achieve very high levels of activity. However, evidence linking sedentary behaviour to metabolic disorders and mortality risk, independent of overall activity, is sufficiently compelling to discourage sedentary behaviour [29–31].
Similarly, in women, occupational activity played a key role in determining activity level but household activity was also important. Statistics Canada has reported that women spend more time doing household chores than do men, even amongst co-habiting partners . These findings are consistent with reports from other recent studies that have examined time spent in leisure-time, occupational, and household activities [19, 33]. As also observed in men, participation in light activity appears to account for an increase in PAL at lower activity levels, while reductions in sedentary time and increases in moderate-to-vigorous activity play more prominent roles in achieving higher activity levels.
On average, very active men and women report about one hour per day in leisure-time activity which complies with most physical activity recommendations for chronic disease prevention [1, 5]. We also observed that the difference in leisure-time activity between those who are very active and those who are inactive is only about 30 minutes in men and 40 minutes in women. In contrast, differences in hours of activity in occupational and household domains were much greater. This is predictable given that the majority of employed people spend much of their day at work and that household chores are usually engaged in on a daily basis. However, the majority of descriptive, etiologic and intervention studies have not focused on these domains. Probert et al  recently reported results suggesting that moderate-to-vigorous occupational physical activity was independently and more strongly associated with a lower risk of diabetes, heart disease and other chronic diseases than was leisure-time physical activity. Household and transportation-related activities were not studied.
Levine et al point out that the main component of TEE is non-exercise activity thermogenesis (NEAT), second only to basal metabolic rate and defined as energy expended above resting with the exclusion of formal exercise [34–36]. Therefore, emphasis on, and ascertainment of only leisure-time or structured activities may misrepresent overall activity level since leisure-time activity may not compensate for prolonged inactivity during the balance of the day. Indeed, inactive men and women engaged in about three hours of total activity per day from all domains and hence spent most of the day inactive. Had these individuals complied with physical activity recommendations to incorporate at least 30 minutes of moderate intensity aerobic activity on most days and an additional 20 minutes of vigorous-intensity activity on at least three days of the week they still would not have increased energy expenditure sufficiently to reclassify them to more active levels based on PAL . It is also worth noting that leisure-time activity was highest amongst those who were retired, yet compared with other employment-status categories, retired men and women had lower levels of activity-related energy expenditure. A recent French study that examined physical activity and sedentary behaviour at retirement reported that while men and women increased leisure-time physical activity at retirement the increase did not compensate for the loss of occupational activity . Hence, examining the unique activity patterns and lifestyle preferences of retired individuals as a subgroup independent of other employment status groups may be advisable in order to identify ways in which overall activity may be increased during this period of transition and major change in lifestyle.
A public-health concern is that those who are most inactive may become even more physically inactive and will soon spend even more time being sedentary as advances in technology continue to replace tasks of high energy expenditure with those requiring lower levels of energy expenditure . Evidence is rapidly mounting to suggest that long periods of sitting time have adverse metabolic and health consequences that are not necessarily compensated for by shorter periods of discretionary leisure-time activity [30, 39–42]. Hence, intervention studies are now underway to examine ways in which energy expenditure can be increased during working hours [43–45]. Traditionally, worksite physical activity programs have interrupted work schedules and lunch breaks in an effort to incorporate them into the day. Walking workstations  and office-place steppers  are not routinely accepted but interest and support for a more integrated 'be active while you work program' will undoubtedly increase as available and feasible options demonstrate their effectiveness .
Few studies have examined average time spent in transportation-related activity but health benefits have been reported for frequent commuting by foot and bicycle [47, 48]. This domain could be targeted for messages that promote commuting by foot and bicycle particularly for those with inflexible work schedules and socioeconomic circumstances that make active forms of transportation more feasible to implement than leisure-time activity .
The strengths and limitations of this study must be considered. A clear strength of this study is the detail with which domain-specific activities were ascertained for time spent sedentary and in light and in moderate-to-vigorous activity. An additional strength is the geographically dispersed population-based sampling that was used to identify participants living in all regions of Alberta. While the response rate was estimated to be 32%, Bryant and colleagues have, compared the cohort with the Alberta component of the Canadian Community Health Survey (Statistics Canada) and observed that the populations were highly comparable on several sociodemographic characteristics . In addition, we limit our analyses to comparisons of domains within and between PAL levels that are observed within this cohort. These methods maintain the internal validity of our results, despite also having excluded participants with missing data (physical activity, height and weight). Generalizability of these findings to other populations will need to be confirmed in future research.
Our findings rely on self-reported physical activity and while over-reporting of physical activity is likely present, these results reveal plausible and informative patterns of physical activity behavior that are generally consistent with our overall understanding of how people spend their time. Furthermore, the Canadian Health Measures Survey (CHMS) collected accelerometer measured physical activity data from a large sample of nationally representative men and women  and recently reported that on average two thirds of waking hours are spent sedentary (9.6 hours for men and 9.8 hours for women). Unfortunately, we did not measure sleep duration in this study since the PYTPAQ was designed to measure activity rather than inactivity. However, if one assumes on average 8 hours of sleep per day, then CHMS results are entirely consistent with our findings of on average a total of 8 hours of reported activity per day from all domains. In the CHMS, contextual information was not collected, precluding the exploration of activity and sedentary behavior across domains. The CHMS results, however, indicate that only 15% of adults meet target levels of 150 minutes per week of moderate-to-vigorous physical activity, further highlighting the critical need for a better understanding of activity patterns that could inform public health programs. In future studies it will be important to use both objective and self-reporting methods to better describe patterns of domain-specific activities that may provide insight into feasible and sustainable strategies that will increase activity and energy expenditure among those who spend most of their day inactive.