ABSTRACT
The limitations of the intervention studies reflect the methodological difficulty in conducting longitudinal research of this nature. Not only does there have to be enough time to allow fitness to improve, but also an adequate number of menstrual cycles need to be observed. In addition, the menstrual cycle alone is difficult to research as menstrual cycle changes vary not only between women, but also between cycles within the same woman. In this context, therefore, cross-sectional studies can be of enormous value and it is to these that people now turn. Medical historians have pointed out that advising moderate exercise for the benefit of the pregnant woman and foetus is not a twentieth-century phenomenon. The cultural climate now supports more active lifestyles for women, and many doctors and pregnant women have been concerned about the amount of activity to engage in.
