We then conducted 2 sets of secondary analyses. First, because of recent interest in possible sex differences in chronic disease risk factors and outcomes, we attempted to see whether there was an interaction between sex and physical activity on inflammation outcomes. In logistic regression models, however, we found that terms representing the interaction between sex and physical activity were not significant predictors of any of the 3 inflammatory outcomes (data not shown). Second, because our categorization of physical activity into tertiles led to fairly broad categories, we sought to examine how a more refined categorization of physical activity would be related to the inflammation outcomes. Thus, we divided physical activity into quartiles (0-1 time, 2-9 times, 10-29 times, and ≥30 times in the previous month). The results from using quartiles in adjusted logistic regression models were fairly similar to those that were obtained when tertiles were used, although the linearity of the association was not as clear. For example, we found that increasing quartiles of activity tended to be associated with a reduced odds of having an elevated CRP level. For those in the second through fourth quartiles, the ORs of having an elevated CRP level compared with those in the first quartile were 0.77, 0.81, and 0.55, respectively (P for trend, .001). For the WBC outcome, the results for the second through fourth quartiles were 0.66, 0.55, and 0.51, respectively (P for trend, .005), compared with the lowest quartile of physical activity. For the fibrinogen outcome, the ORs for the second through fourth quartiles were 0.81, 0.82, and 0.77, respectively (P for trend, .17), compared with the first quartile.