This study used accelerometry to examine the prevalence of physical activity and sedentary behavior as well as the relationships of demographic, anthropometric and lifestyle characteristics with physical activity and sedentary behavior in urban Chinese adults. In this urban Shanghai population, physical activity levels decreased and sedentary behavior increased across consecutive age groups, similar to previous reports of accelerometer-measured physical activity in predominantly Caucasian adult populations.16,25
Furthermore, men and women with a greater BMI or waist-to-hip ratio were less physically active than lean individuals, and current cigarette smokers engaged in less physical activity than those who never or formerly smoked. In contrast with observations in Western populations,16,25
however, men were not more physically active than women. In fact, women spent more time in light physical activity than did men.
On average, participants spent the most time per day in sedentary behavior, but 98% of participants accumulated at least 30 minutes per day of moderate-to-vigorous physical activity. When a higher cut-point for accelerometer-measured moderate-to-vigorous activity (1952 ct/min) was employed, 56% of the study population achieved this level of physical activity, similar to a Swedish study25
in which 95% of participants accumulated 30 min/day of moderate-to-vigorous activity when the cut-point for defining moderate-to-vigorous activity was set at 760 ct/min or 52% when the cut-point was set at 1952 ct/min. Despite the influence of the selected moderate-to-vigorous cut-point on physical activity prevalence, associations with demographic, anthropometric and lifestyle factors were not sensitive to any change in cut-points.
The present study observed differences between accelerometry and self-report in the estimation of time spent in physical activity and sedentary behavior. Participants self-reported more moderate-to-vigorous activity than was measured by accelerometry, despite the relatively low cut-point for defining moderate-to-vigorous activity. This result could derive from participants over-reporting moderate intensity activities on the PAQ or from failure of the accelerometer to capture moderate intensity activities such as household chores, bicycling or swimming. For example, 45% of the present cohort reported cycling for transport or getting about on the PAQ (median 27 min/day), thus it is possible that the accelerometer underestimated total and moderate-to-vigorous activity. Similar to a study in Dutch adults,26
better agreement was observed between accelerometer-measured and self-reported moderate-to-vigorous activity after excluding cycling (median of 76 min/day without cycling), although associations with participant characteristics did not change. In addition, less sedentary behavior was reported on the PAQ compared with accelerometer measurement, which may have resulted from participants under-reporting sedentary time,27,28
from under-ascertainment of sedentary behavior by the PAQ, or from overestimation of sedentary behavior by accelerometry. Most likely, a combination of the limitations of both instruments contributed to these discrepancies.
The demographic, anthropometric and lifestyle correlates of accelerometer-measured physical activity and sedentary behavior in this Shanghai population were largely similar to those characteristics observed in Western populations.9,16,25,29
In contrast with previous evidence based on self-reported physical activity and sedentary behavior,9,29
however, neither male gender nor attained education was positively associated with accelerometer-measured physical activity. Furthermore, distinct associations of gender and attained education with self-reported versus objectively measured physical activity and sedentary behavior were observed. Together, these results suggest that population subgroup–specific physical activity levels and/or physical activity reporting patterns exist.
For example, the authors did not observe an association of gender with accelerometer-measured moderate-to-vigorous activity, but women self-reported spending more time in moderate-to-vigorous activity than men. The bulk of the literature supports a higher level of activity among men,9,29
thus it is conceivable that women in the present study over-reported time spent in activities30
such as cooking, cleaning, and laundry that are more prevalent among women than men10,31,32
and are not well captured by accelerometry.33
Alternatively, women may have overestimated the intensity of domestic activities when self-reporting, as accelerometer results showed that women were more likely than men to engage in light activity. While accelerometer-measured physical activity and sedentary behavior were not associated with attained education in the current cohort or in one other study,26
self-reported sedentary behavior was positively related to level of educational attainment. This finding is inconsistent with many,9,29,34–36
but not all37,38
studies of self-reported physical activity levels in relation to educational attainment.
Age was inversely associated with accelerometer-measured total activity and moderate-to-vigorous activity, suggesting that older people may be an ideal subgroup for physical activity promotion. Yet older individuals were more likely to self-report a high level of moderate-to-vigorous activity, which is consistent with previous studies in Shanghai10,11
and in other Asian adults,39
but is in contrast with two reviews in Western adults.9,29
The observed associations of self-reported moderate-to-vigorous activity and sedentary behavior with age may have resulted from imprecise reporting by older individuals, from cognitive issues of recall or from differential perception of exertion by older compared with younger individuals.
Results from accelerometer measurements indicated that obese individuals and those with central adiposity were less active than leaner people, but individuals with a greater BMI self-reported suggestively more total activity. A positive association of BMI with self-reported physical activity is consistent with previous studies in Shanghai,10,11
and is intriguing since these relationships oppose those generally observed in Western populations for self-reported9,40,41
and objectively measured25,42,43
physical activity. It is possible that this unexpected association is the result of overweight and obese adults systematically over-reporting their physical activity levels, as noted in several studies,26,42,44–47
or the PAQ may misclassify activity levels among overweight individuals for whom less strenuous activities are likely of higher relative intensity.48
Alternatively, if obese individuals wore the accelerometer positioned at a tilt, the monitor may have underestimated activity counts.49
Similar to previous reports,9–11,50
inverse associations of physical activity with cigarette smoking were observed, although associations were significant for accelerometer-measured total and moderate-to-vigorous activity only. A positive relationship of physical activity variables with total energy intake across instruments is consistent with previous observations in Shanghai.10,11
The cross-sectional design of this analysis limits further interpretation of the nature of relationships of physical activity and sedentary behavior with demographic, anthropometric and lifestyle factors. Furthermore, although characteristics of the study population were similar to the larger, population-based SWHS and SMHS cohorts in terms of age, BMI, education and smoking status (data not shown),51,52
the physical activity level of the study population may not be representative of urban Shanghai adults, as individuals who agree to participate in a study with such extensive measurement may differ from the general population. An additional limitation is that many of the participant characteristics evaluated in this study were measured prior to the physical activity measurement period. Although occupation, smoking status, BMI, waist-to-hip ratio and possibly total energy intake may have changed over time, gender and attained education are likely to be stable. In order to discern the direction and magnitude of these associations and to determine whether these characteristics determine or are the result of physical activity patterns, prospective studies or controlled trials are required.
In summary, this study of objectively measured physical activity among urban men and women from Shanghai, China, found that older people, obese individuals, and current cigarette smokers exhibited significantly lower levels of physical activity than their younger, more lean, and nonsmoking counterparts. The authors also present an unexpected result that women spent more time in light physical activity than men. In addition, no relationship of educational attainment to total physical activity or time spent sedentary was observed. Further investigation of physical activity patterns using objective methods will be necessary to determine whether declining physical activity levels are related to an increasing burden of chronic disease in China and beyond. Such work should also help to identify population subgroups that could benefit most from physical activity and public health promotion programs.