The influence of strenuous muscle stimulation on the menarche.

Nowadays, the average age at which menarche begins is lowering by three to four years every century, that is, four months every decade, according to both Japanese, and European and American annual changes of the average age. It emerged that the menarche shows a tendency to occur later in female gymnasts, because of the influence of strenuous muscle stimulation, and the fact that a higher level of technic is required in gymnastic games each year. These conclusions have been drawn from replies submitted to a questionnaire distributed among a relatively small number of gymnasts who participated in the competitions including the Inter High School Championship and the World Cup Championship. For example, at the age of 14, the percentage of women who had menstruated is almost 100% among women in general, but only 24% among World Cup Championship gymnasts, the average age at menarche of the latter being later than that of the former by as many as 3 years. At the age of 16, the percentage of women who had menstruated is 100% among women in general, but on the other hand, it is only 60% among World Cup Championship gymnasts, in other words, only a low percentage of women, of the latter group, had menstruated. Finally in our study, we established that the age at menarche of gymnasts is three or five years later than that of women in general. From our study, we concluded that the excessive burden imposed on muscles might cause an abnormal menstrual cycle, and the influence on menstruation would be considerable.