The researchers collected information on height, weight, reproductive and medical history, plus lifestyle and behavioral details, and then sent out follow-up questionnaires by email every two months for 12 months, or until a woman became pregnant.
At the study's start, the women were asked about the average number of hours per week they exercised and about what types of moderate or vigorous physical activity they performed. Running, fast cycling, aerobics, gymnastics and swimming were considered vigorous. Brisk walking, leisurely cycling, golfing and gardening were defined as moderate.
The participants were categorized by their exercise levels and the results were evaluated according to body mass index (BMI, a ratio of weight to height). A BMI over 25 is considered overweight or obese.
While moderate physical activity was linked to becoming pregnant faster across all BMI ranges, the researchers found that there was an "inverse association" between vigorous physical activity and how long it took to become pregnant for normal-weight women (a BMI under 25). In overweight or obese women, there was no link between vigorous exercise and a longer time to pregnancy.
The study findings, which did not prove a cause-and-effect relationship, were published March 15 in the journal Fertility and Sterility.
Wise noted that in other research, being overweight or obese has been associated with lower fertility rates compared to normal-weight women. Obesity has also been associated with menstrual cycle disturbances. She said increased physical activity in this study might reverse the harmful effects of obesity and improve the overweight women's overall fertility rates.
The exact mechanisms for why physical activity might enhance fertility in overweight and ob
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