(49.2)(51.2)(53.1)(56.1)(57.1)(59.1)(61.0)(63.0)(65.0)(66.9) (68.9) (70.9)

Height (cm) (inches in parentheses)

Figure 4 The minimal weight necessary for a particular height for onset of menstrual cycles is indicated on the weight scale by the 10th percentile diagonal line of total water/body weight percent, 59.8%, as it crosses the vertical height lines. The height growth of girls must be completed or approaching completion. For example, a 15-year-old girl whose completed height is 165cm (65 in.) should weigh at least 43.6kg (96lb) before menstrual cycles can be expected to start. (Adapted from Frisch and McArthur (1974) Menstrual cycles: Fatness as a determinant of minimum weight for height necessary for their maintenance or onset. Science 185: 949-951, with permission from Science.)

training, the incidence of oligomenorrhea and ame-norrhea increased in both groups.

As other workers have found, plasma gonadotro-pins and estrogen levels were in the low-normal range in this study for the athletes with irregular cycles or amenorrhea. Progesterone was at the folli-cular phase level. Thyroid hormones, however, were in the normal range. These athletes had increased muscularity and decreased adiposity compared to nonathletes. The explanation for their menstrual disturbances may therefore be the same as that for dieting, nonathletic women—too little fat in relation to lean mass. Some of the swimmers and track and field athletes were above average weight for height.

A raised lean mass:fat ratio may nevertheless have caused their menstrual problems because their body weight represented a greater amount of muscle and less adipose tissue than the same weight of nonath-letic women.

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