Thirty female smokers ( Mean ( M ) age = 25.7 years , Standard Deviation ( SD ) = 5.5 ; M weeks pregnant = 18.2 , SD = 5.3 ; Fagerstrom Test for Cigarette Dependence = 3.3 , SD = 2.2 ; M 9.3 cigarettes/day , SD = 4.7 ; M hours abstained = 17.2 , SD = 2.8 ) were randomized to 20 min of mild-to-moderate intensity exercise ( EC ; n = 14 ) or passive ( PC ; n = 16 ) condition .