Synergy between thinness and intensive sports activity in delaying menarche.

In a study to assess the effects of intensive physical activity and thinness on menarche records of 648 girls aged 10-14 were analysed. The girls were classified as thin or not thin on the basis of their body mass index, and whether or not they engaged in intensive sports activity was established. The presence of either thinness or intensive sports activity was associated with roughly a twofold decrease in the proportion of girls who had reached menarche; the presence of both factors was associated with roughly a fourfold decrease. These results did not appear to depend on age. Thus intensive sports activity and thinness appear to have a synergistic effect in delaying menarche.