2.1. Participants
Recruitment started in December 2006 and was com- pleted in August 2007. Participants were recruited from three sources; the University of Tokyo Hospital and two public health centers located in the same district. Women living in the Tokyo area in Japan, signed up for this stu- dy until one month postpartum. Women voluntarily ap- plied for participation in the exercise class. Eligible women were more than 20 years of age without any me- dical complications who expected to give birth between January and July 2007. Women with restricted physical activity or suffering from psychiatric disorders were ex- cluded from the study.